Two potentially life-friendly planets found orbiting a nearby star | Hacker News Reader

Two potentially life-friendly planets found orbiting a nearby star

nationalgeographic.com

612 pointsTuringTest371 comments

Being that close also offers us a better ability to examine it. The nearer the star, the more arc-seconds (or tiny fractions thereof) the star will appear in telescopes. 12ly is ridiculously close!

It also tells us something interesting. If we presume there's nothing special about our little corner of the universe, then the distance to the nearest potentially habitable planets gives us an estimate of how many habitable planets are out there. Only 12ly away and that one has maybe two habitable planets? That tells me the universe is teaming with potential homes for life.

Yes 12 ly is amazingly close!

> If we presume there's nothing special about our little corner of the universe, then the distance to the nearest potentially habitable planets gives us an estimate of how many habitable planets are out there

I would put a slight caveat to this - I would argue we do know there's something "special" about our little corner of the galaxy, at least - we are in the continuously habitable zone - for example, there are billions of stars at higher densities closer to the core whose planets are likely uninhabitable due to toxic levels of radiation, GRBs, etc. So I actually might expect other planets near us to be more habitable on average than at least some other places in our galaxy.

But I also think it's too soon to know how potentially habitable these planets are, until we have a chance to check a bunch of other things on the checklist, like the long-term stability of the sun's output and the planet's orbits, the frequency of destructive solar flares, the frequency of asteroid bombardments (if there are no Jupiters to absorb them), etc.

Regardless the close distance should make it much easier to answer these sorts of questions than it would be far planets much farther away, and I'm excited to see what we can learn in the coming years.

Wouldn't each system's star do a decent job of pushing back extra-solar radiation? Up to a point, obviously, but it would seem that planetary background radiation levels aren't a direct function of solar density.

It's not the density of the star but the density of stars. Dense clusters like those found in the center of our galaxy create a lot of secondary effects like bigger stars pulling matter away from smaller stars (creating lots of background radiation and matter floating around) and then stars plow through those interstellar clouds, creating deadly bursts capable of cooking entire planets, stripping away their atmospheres, etc. In the center of the galaxy, these events happen so frequently that it's extremely unlikely life on any of the planets would survive long enough to evolve beyond simple single celled organisms.

I'm talking about the local solar density, not an individual star's density. Obviously that has little effect on the habitable zone of a planet.

My question was about the ability of a system's star's own radiation to ward off extra-solar radiation and what kind of limitations we are aware of.

Believe you are thinking of solar wind? That might counteract another source, but don't believe light radiation would be affected.

Solar wind is a type of solar radiation. I thought perhaps a charged field of particles with an outward force could act at least partially as a shield in for some higher frequencies of electromagnetic waves.

Electromagnetic radiation from one star does not repel electromagnetic radiation from other stars. If it did, we wouldn’t be able to see stars at night from the Earth.

> If it did, we wouldn’t be able to see stars at night from the Earth.

Ha! I love straighforward sanity checks like this. My initial reaction was to ask myself about photon-photon collisions which are im fact possible, but your comment gives a nice Fermi bound on how rare such events actually are. Cool!

Photon-photon collisions are still technically possible... I remember a professor mentioning this as one question he got in grad school... draw out the Feynman diagram and you see a vanishingly small probability of photon-photon interaction.

But yeah. Ionized particles like Galactic Cosmic Rays can be repelled by the local stellar magnetic field, but mostly the lower energy rays are deflected. Higher energy -to-charge-ratio GCRs can punch right through the weak stellar magnetic field, just like do for our Sun’s interplanetary magnetic field.

Thank you for understanding my question before reaching for dismissal :)

I knew low-energy waves are partially deflected, I just wasn't sure about high-energy waves. Makes sense!

I should have been more clear in my question. Solar wind is a form of solar radiation, and I was curious about the effect of solar wind + the magnetic field that carries it would have on some frequencies of electromagnetic waves.

I would expect mid-frequency radiation such as visible light to remain largely unaffected, I was thinking more about its effect on high-frequency extra-solar radiation. And it's likely not correct to visualize this as individual photons colliding but rather wave interference.

Here is an article explaining the effect [0]. An excerpt:

"The interplanetary magnetic field, which is embedded in the solar wind, deflects low-energy cosmic rays from us at the outer reaches of our solar system, decreasing the flux of these cosmic rays that reach us at Earth."

[0] https://aasnova.org/2017/12/01/a-shifting-shield-provides-pr...

It sounds like you're thinking of the heliosphere, which is the bubble in the interstellar medium created by the solar wind. The solar wind, in turn, is created by outflowing plasma from the Sun, and is also responsible for auroras and comet tails. The details of how far from the sun the heliosphere extends are complex, but it encompasses all the known planets.

The heliosphere does provide us with a significant amount of protect from cosmic rays, which aren't actually electromagnetic radiation. Cosmic rays are extremely energetic particles, typically protons, coming in from outside the solar system. The Earth's atmosphere also does a good job stopping cosmic rays, which means their primarily a hazard to spacecraft, both manned an unmanned. (I don't know what effect cosmic rays would ultimately have on Earth if we didn't have the protection of both the heliosphere and our own atmosphere, but I know they have been investigated for links to mass extinctions.) They're a threat to space travel because they cause soft errors in electronics, and DNA and other radiation damage to human beings.

The Sun's magnetic field - aka the interplanetary magnetic field or heliospheric magnetic field - travels with the solar wind and fills the solar system. It is magnetically coupled to solar system bodies like the Earth and Jupiter. As an amateur astronomer, the heliospheric magnetic field doesn't have any significant effects on photons coming into the solar system.

That is incorrect. Energetic particles are radiation. Radiation isn't just photons.

I don't think you understood my question very well because none of what you presented is new to me nor is it what I asked about. Still, thank you for the time and effort.

Nope! Some stars are in a stable orbit in a region with some NASTY orbiting interlopers who are eating star systems every million years and have just not made their way to them yet.

We have made it at least a billion or so without getting too close to a nasty body so that says something about the region around us.

I'm guessing you've read Incandescence by Greg Egan?

It explores the possibility that general relativity could be discovered by a pre-industrial civilisation living inside an asteroid in a very tight orbit of one those nasty interlopers.

Egan is one of my all-time favorite SF authors. Was delighted and surprised to find his name popping up in some nitty-gritty, research-level algebra discussions recently. I haven't heard of Incadescence so it's definitely going on the list. Am also intrigued by Dichronauts too! Have you read it?

I often hear about the LY unit of distance. Why is it that we are still discovering things which are close to us in LY units? Wouldn’t we discover things at a distance of 5xLY before discovering things at a distance of 100xLY?

Things that are very luminous can be seen much further away than things that are very dim.

This particular star is a tiny red dwarf, which is so dim we only just found the star itself in 2003.

Our best planet-finding methods depend on finding signals in the light output of the host star. This is relatively insensitive to distance, but very sensitive to the properties of the star.

> Only 12ly away and that one has maybe two habitable planets? That tells me the universe is teaming with potential homes for life.

This seems like the birthday problem in statistics [0] - that if you have 30 people, it's likely that two people have the same birthday.

However, the problem that could also exist (in our corner of the galaxy) that everyone else has a birthday far away from ours, and nobody else shares a birthday on the same day with anyone else. (in other words, we happen to be the two people who share the same corner of the galaxy, but everyone else is far away and separate - i.e. no other clustering).

Not disagreeing with you, and it does give us hope, but randomness is a bch that can make everything look different from how it actually is.

[0] - https://en.wikipedia.org/wiki/Birthday_problem

The birthday paradox works because you are looking for a pair that has the same birthday, regardless of what date that birthday is. It doesn't work in the habitable planet sense because you would be essentially locking the birthday to a fixed date.

Yes. How many people do you need in a room to be confident that one of them has the same birthday as you?

How confident? Even with an even distribution of birthdays it's possible to have a billion people in the room that don't share your birthday. Very unlikely, but as there's only about 20 million people with your birthday, and 7 billion without, it's quite doable.

"Very unlikely" is a severe understatement. With only 100k people, the odds of no one else having your birthday is 10^-120. With a million people, it is 10^-1192.

And with a billion people... apparently, there are over a million zeroes between the decimal place and the first non-zero number. That is a pretty damn small probability.

Here is the code I used in python 3:

   from decimal import Decimal
   print((Decimal(364) / Decimal(365)) ** num_people)

quite, hence "how confident"

There's other things as play. Imagine you, born on July 15th, walked into a room with 1000 people. You'd be fairly confident someone will be born on July 15?

What if I then told you it was the annual astrology get together of Capricorns?

Sure, but you did say "even distribution".

Assuming a uniform distribution, the probability is 1/365 for any person#. Those probabilities add up linearly if the people are guaranteed to have different birthdays (union/OR). Otherwise the probability of NOT having someone with the same birthday goes down exponentially as a an exponential power of the fraction 364/365 (intersection of complement/AND NOT)

It’s exactly what you would expect from classical combinatorics with cards with or without replacement. Your term “confident” is vague.

I produced a series called Thinking Mathematically on youtube that makes all of this and other related topics clear for anyone... I recommend checking it out!

https://m.youtube.com/channel/UCuge8p-oYsKSU0rDMy7jJlA

And here are the notes for it

http://magarshak.com/math/numbers.pdf

http://magarshak.com/math/sets.pdf

http://magarshak.com/math/logic.pdf

# if we exclude all people born leap years

> Assuming a uniform distribution, the probability is 1/365 for any person#. Those probabilities add up linearly if the people are guaranteed to have different birthdays (union/OR). Otherwise the probability of NOT having someone with the same birthday goes down exponentially as a an exponential power of the fraction 364/365 (intersection of complement/AND NOT)

Why would we assume a uniform distribution of birthdays? For example, birthdays occurring on the 31st of a month are probably less likely to occur on average given that every month does not have 31 days. This is just one example and doesn't even go into seasonality of conception cycles.

To simplify. Mathematical models don’t perfectly capture all the details usually.

You need 253 people in the room to have > 50% probability that one will have the same birthday as you.

1 - ((365 - 1)/365)^253 = 0.5005

If birthdays are assumed to be distributed symmetrically. If you were born in august you'd need ~12 fewer people and for April you'd need ~12 more.[1]

Not sure how that looks for the worlds population probably averages out pretty well regardless.

[1]: https://www.panix.com/~murphy/bday.html

I'm locking the area to a specific region. If I divide the universe into 365 discrete areas, the problem is exactly the same.

If you're locking the area to a fixed area out of the 365 discrete areas, the birthday paradox isn't applicable anymore. Birthday paradox only says something about whether a pair exists among all areas.

So you're in a room with N people and learn that somebody else shares your birthday. Can you conclude that is this likely that other people in the room also share the birthday with somebody else?

If you already assume the room is a representative sample from a population where birthdays are uniformly distributed, it doesn't tell you anything.

But if you aren't certain about that, it makes it less likely that everyone else with your birthday has been ritually murdered or otherwise systematically excluded from the room, and slightly more likely that you're at a convention dedicated to people with your birthday.

Thanks for posting. This is exactly what I was trying to say (but you said it better).

One more benefit is, we are looking at very recent past instead of hundred and thousands year past in comparative other planted.

Light Year has a technical meaning, but it is so large that I can't relate to it at all. So I tried to figure out a different unit of measure, and I came up with what I call an "Earth Escape Year" or EEY.

From Earth, the escape velocity for our solar system is 42.1 km/s. EEY is the distance traveled for 1 year at that escape velocity. It is the maximum amount of time it would take to reach an interstellar object directly launching from Earth -- any slower and you can't get there at all. 1 LY = 7,121 Escape Years. The upper bound time to reach these planets is about 85k EEY.

Sorry, but this does not make sense in the way you intended. Your 42.1 km/s escape velocity "from earth" is the velocity you need, relative to the sun, at earth's orbital distance from the sun, to escape from the solar system [1].

As you get farther away from the center of gravity, your speed gradually slows down and reaches zero at infinity [2].

So your maximum amount of time for interstellar travel calculation is flawed and underestimates travel time by assumedly few orders of magnitude.

[1] https://encyclopedia2.thefreedictionary.com/Solar+System+Esc...

[2] https://en.wikipedia.org/wiki/Escape_velocity

The note that it's an old star makes me worry though. If they're older then us, and habitable, were they inhabited?

Our current era is a few hundred years of real, directed technological development. A few thousands years either side of that and who knows what we'd be looking at, but you imagine that - hopefully - the general progression of technology is forward.

So if they were inhabited, what happened to them? Are they exactly at our level of development? Earlier? Hopefully. Because later poses some real big questions - does technology top out about where we are now - no FTL travel, no really big radio transmitters or stellar engineering? No probes to nearby star systems? Did they even make it past the nuclear age, or avoid wrecking their climate?

One thing's for sure - if there's really 2 habitable planets, with liquid water, then we've got a hell of a target to point James Webb at when it launches - an infrared spectrum star should mean any plant life is well optimized to towards the redder end of the spectrum - we should see some type of chlorophyll.

> Are they exactly at our level of development?

If so, then at just 12ly away, we could converse with them within (many of) our lifetimes.

What are the chances that would've already happened given how long we've been sending life made RF off the planet? A 24 year exchange isn't awful.

12 light years is a long way for a signal to go without attenuating into noise.

What about things like LIGO? It can detect changes in length corresponding to 1/10,000th the width of a proton. Surely communicating over RF with another planet should be within our reach, no?

Could we?

Despite stellar levels of energy being emitted, this star itself was only detected in 2003. We have to use the Deep Space Network to communicate with probes light-hours away.

I'm no expert so it very well may be possible, but 12 LY is still Very far.

It wouldn't be possible to send a message literally today, using existing structures. If we had a reason to, we could certainly develop and build new systems that could bridge the distance.

The main key difference is that the send/receive ends would be symmetric. DSN has to counterbalance the incredibly small size and power limits on the other end of its connections.

The odds of that are effectively zero. Over a multi-billion year development line, being within 100 years of one-another is effectively impossible.

They are either unevolved animals, or have already merged into the Great AI or whatever happens when intelligent species evolve.

The note that it's an old star makes me worry though. If they're older than us, and habitable, were they inhabited?

Many dwarf stars have more solar flares than our sun, while their planets are closer. Teegarden's star is supposed to be very calm right now. I have no idea if that is likely to be true over most of the past 8 billion years. The amount of water they gather may be smaller, and their closer planets may not be able to retain water as well.

So if they were inhabited, what happened to them?

Let's say the origin of life is a million to one filter, and the successful development of sentience is another million to one filter. Those are actually pretty high odds for those two events, and the combination of those two togehter is enough to make it likely we're alone in the Milky Way.

Since most of the star's energy is emitted in the infrared, which is a more diffuse form of energy, does this limit the potential of photosynthetic organisms to gain a disruptive evolutionary advantage? (Maybe not. It's still free energy from the sky.)

> Let's say the origin of life is a million to one filter, and the successful development of sentience is another million to one filter. Those are actually pretty high odds for those two events, and the combination of those two togehter is enough to make it likely we're alone in the Milky Way.

I mean, not really? Doesn't the Milky Way have ~100 billion stars?

(million: 1)^2 * 100 billion gives an estimate of ~0.1 stars in the Milky Way that host life.

Indeed. But then developed it hitch hikes a ride on asteroids and spreads virally. See Dr Zubrin’s recent discussions https://www.centauri-dreams.org/2017/12/21/interstellar-comm...

>Let's say the origin of life is a million to one filter, and the successful development of sentience is another million to one filter. Those are actually pretty high odds for those two events, and the combination of those two togehter is enough to make it likely we're alone in the Milky Way.

The Drake equation has 7 terms. When it was first proposed, all but the first were complete unknowns. We're just barely starting to gather enough data to start tightening our guesses for the next two. The rest (which include the two you used) are complete unknowns. You say "those are actually pretty high odds", but by whose measure? There's exactly one data point to support that assertion, and right now that data point suggests that the odds are 100% (with an uncertainty also approaching 100%). We're still decades away from really having the data to assert anything at all about the presence of life outside of our solar system with confidence.

We should be able to make some approximations regarding sentience. If we only consider Homo Sapiens Sapiens, then yeah we only have one data point. If we consider other extinct hominid species, we have more. If we consider dolphins, ravens, etc - we start to have a fuller picture and can make some (at least slightly) informed estimates to that term

You're still extrapolating from a single life-creation event. Until we find a second planet that evolved life entirely separately from Earth, we have exactly zero meaningful information about the genesis of life. Without knowing what percentage of life is roughly similar to life on Earth, we have exactly zero meaningful information about how valid Earth-centric extrapolations are.

> Since most of the star's energy is emitted in the infrared ... does this limit the potential of photosynthetic organisms ... ?

I'm not any sort of biologist or chemist, so somebody please correct me if I'm wrong, but...

If you specifically meant photosynthesis by terran chlorophyll, then yes, I suppose it would be less effective. However, I could imagine photosynthetic life to evolve under those conditions that uses some other compound to capture and convert the energy.

Also to consider is the amount of radiation (light, etc.) available on the surface, which can be figured as a formula of the radiation emitted by the sun, distance from the sun to the planet, and attenuation of radiation by the atmosphere. Much of the light (and other energy) emitted by a sun does not reach the surface of a planet with an atmosphere. The particulars are, of course, dependent on the atmospheric composition, but generally I would expect infrared light, with longer wavelengths than visible light, to better penetrate the atmosphere and be more available to life on the surface.

Do we know that intelligent life is an evolutionary inevitability? Most of these discussions seem to assume that it is, but I haven't read any biologists mention this.

Or to take it a step further, whether it is inevitable that intelligent life will have both the capability and opportunity to make their presence known. Maybe some planets are full of superintelligent dolphin-like creatures that had their development stall because they didn't have the dexterity to manipulate tools to the extent that sapiens can. Or maybe there is intelligent life on a planet similar to Europa that never prioritized space exploration/communication because instead of an Earthlike atmosphere their planet is surrounded by miles of ice.

What we can infer from the gradual evolution of various species on Earth is that brains do seem to evolve larger, more complex, more efficient - though are often bottlenecked by other costs.

If you look at a snapshot of all life on Earth over tens of millions of years, the average brain size of dominant species has clearly increased.

Tens of millions of years is a pretty small snapshot to use. Brains have existed on earth for approximately 500 million years. Life for about 7 times that.

I don't think we even know that a planet that's had life twice as long gets twice as much evolution. The rate of evolutionary change is far from constant, and whatever factors affect that rate might be different on some other planet.

> So if they were inhabited, what happened to them? Are they exactly at our level of development? Earlier? Hopefully. Because later poses some real big questions - does technology top out about where we are now - no FTL travel, no really big radio transmitters or stellar engineering? No probes to nearby star systems? Did they even make it past the nuclear age, or avoid wrecking their climate?

You get more than one chance. While finding intelligent life would be great, finding any life is nearly as great. We might not catch them at a comparable technological moment, but over 8 billion years, intelligent life could have come and gone many times. All we need are some biosignatures to confirm that something's out there, and exploration will kick into overdrive.

Actually if we find life on other planets that is bad news for us as a species:

https://www.technologyreview.com/s/409936/where-are-they/

> While finding intelligent life would be great, finding any life is nearly as great.

That would actually be worrisome. If we found and detected microorganisms on nearby planet e.g 12 light years away from earth, then that means we are probably headed for extinction.

The reason is the theory of the Great Filter. Given that we have not been able to observe any kind of activity outside of our solar system, it means that either life is rarer than we think or that entire civilisations go extinct pretty quickly.

If we find microorganism on a nearby planet, the logical conclusion is that life is not as rare as we think but evolved civilisation such as ours simply go extinct in a relatively short amount of time.

The Great Filter may be ahead of us.

Have we done anything that we'd be able to detect from 12 ly?

Our radio transmission bubble is far beyond 12ly. The question is how sensitive an instrument we'd need to detect it. IIRC, there are some pretty big bursts in ther along with the general noise.

There'd also be significant signatures in the composition of our atmosphere.

The window for detection at different power levels is probably quite small.

Very early radio would be somewhat weak. The middle phase of analog transmission probably has some higher power levels. The digital phase would coincide with rapid decreases in detectability.

That assumes every planet capable of supporting life a) has life and b) develops intelligent life. If only 1% of planets capable of supporting life develops life and only 1% of those develop intelligent life then it is extremely unlikely these two nearby planets would have any life at all. Even if you bump the odds to 10% or even 33% the odds are still against it.

For sake of argument assume we (or they?) won the lottery and intelligent life exists. Make an even larger stretch and assume that life is technologically capable, has been for 10,000 years, and didn't destroy themselves (achieving a stable population size and reasonable resource usage). Even then the odds are against us detecting any kind of radio transmissions.

I think you have a slight misunderstanding about the great filter.

If we found only microorganisms on the other plant that should indicate that the filter is behind us, life having died out on that planet before even reaching large scale organisms let alone technology.

If we find ruins of civilization and technology on the planet at either about the same stage as us or more advanced, then we can assume that the filter is ahead of us.

Not so. All we know from finding micro organisms (or any other form) is that the filter is after that stage. It may well be between micro organisms and us but that seems unlikely.

ok, assuming you mean that nuclear war is the threat to all civilizations (because once we advance to the point of developing nukes, eventually some asshole deploys them irrationally).. why isn't this a solved problem? I.e: create underground societies that are nuclear-powered and sustainable for centuries, and impervious to nuclear attack?

Not necessarily. Live != civilization, so just because many planets may have developed live (or obtained it via panspermia) but only very few (or one) have developed multi-cellular live (which even on earth is quite recent) and even less a civilization comparable to us humans.

I think there’s no technological barrier there, but cultural choice: if there’s no good economic reason to go to space (ie That has a high enough rate of return within a short enough period of time), we may just die out before doing any of that stuff. I think about that every time someone argues human spaceflight is worthless. I don’t think they’re wrong in the short-term, but the societal consequences are the same as if the entire species just decides to stop having children entirely because there’s no good economic reason to do so.

Especially thinking about this near the anniversary of Apollo. What if that was the greatest extent of human travel in space? To me, that’s so sad.

https://m.xkcd.com/893/ “The universe is probably littered with the one-planet graves of cultures which made the sensible economic decision that there's no good reason to go into space--each discovered, studied, and remembered by the ones who made the irrational decision.”

in view of what you're asking about the development of technology, and whether or not civs tend to "peak out" around our current level, i think back to the drake equation* and the coefficients for the likelihood of intelligence evolving and the likelihood of intelligent life creating technology that emits detectable signs of that civilization (space infrastructure, dyson swarms, nuclear isotopes in atmosphere , etc). Those 2 being Fi and Fc.

Id like to share whata I think is one of the cheeriest possibilities:

- that earth-like planets are rather common (we have 3 such planets in the Sol system),

- basic life is less common but still pretty common (decent chance mars could have had life, maybe europa's sub-ice oceans has it now... conceivable at least),

- but what isnt super common is the development of human-level intelligence, and even less common is developing technology to the point we are currently at

- but (and this is the most cheery part) even though human-level intelligence and our current tech level is very uncommon, that once a species develops that level of tech, barring a catastrophic extinction event (DNA-hyper-plauge, mega-asteroid, all the nukes getting launched at once), that that life is likely to continue for a long time.

I say that last part because even with our current problems with the Anthropocene extinction and climate degradation, it's likely that humans will be here in 100 or 1,000 or 10,000 years.

Worst case could be even be so bad as humanity entering its first ever world-wide dark age (as opposed to regional dark ages) where higher technology is less prolific and more concentrated. Even given something like that that - which i think is neither a certainty or even a reasonable conception of the future - humanity would continue and 10 generations on our decedents would start something akin to a second Renaissance.

So what I'm getting at is once a civilization develops roughly our level of technology, it may be very durable even in the face of temporary disasters and darkness.

Now, as far as the fancy space tech you bring up, yeah, who knows... It seems like those tech have a big issue beyond Physics, which is the Fermi Paradox.

If say, Dyson Swarms were "possible" (they really seem like they should be... we could start building one now), then we should be seeing evidence of that all over the universe from those civs who've come before us and build them. That's scary to think about, that maybe we're the first life to get to this level in the universe. Then again, maybe advanced civs learn early to obfuscate the signs of their existence, or perhaps even use technology that we don't recognize / cant detect.

A great Youtuber named Isaac Arthur talks about both the drake equation and the futurist's existential bummer about the Fermi Paradox. Check him out if anything i bring up here sounds cool.

*Drake Equation is a simple(ish) way of plotting out how likely / many adv civs are out there based on the likleyhood of some conditions. From wiki - The Drake equation is:

    N = R ∗ ⋅ f p ⋅ n e ⋅ f l ⋅ f i ⋅ f c ⋅ L

where:

    N = the number of civilizations in our galaxy with which communication might be possible (i.e. which are on our current past light cone);

and

    R∗ = the average rate of star formation in our galaxy
    fp = the fraction of those stars that have planets
    ne = the average number of planets that can potentially support life per star that has planets
    fl = the fraction of planets that could support life that actually develop life at some point
    fi = the fraction of planets with life that actually go on to develop intelligent life (civilizations)
    fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
    L = the length of time for which such civilizations release detectable signals into space[

https://en.wikipedia.org/wiki/Drake_equation

> you imagine that - hopefully - the general progression of technology is forward.

I think this might be the key myth of our times. Our entire history is a blink of an eye along the timescales Earth normally changes on. But the last couple hundred years really takes the cake - within a couple human lifespans, we've gone from a lifestyle broadly recognizable to any human from history, to some kind of ravenous sci-fi techno-megamind with spaceships and robots. We should be scared - even on our human timescales things are changing rapidly. On Earth timescales, this is not a steady state but an event - a sudden, runaway, exponential, violent event.

We have such a short perspective that we are lulled into thinking of it as a "natural progression". But that's like jumping off a cliff and concluding the natural progression is freefall. We know this state of affairs cannot possibly last. Why keep pretending?

What I always find massively baffling is, that any transmitted and recorded history is less than 15,000 vears old.

First hints at sedentariness appear around the construction of Göbleki Tepe [1].

[1] https://en.wikipedia.org/wiki/G%C3%B6bekli_Tepe

However, biologically speaking we has Homo sapiens sapiensis are around for approximately 250,000 years.

That's ~6% of our biological existence where we suddenly went from running around, building like 3 stone-wood tools and wearing animal skins to communicating across the planet in real-time.

I totally agree. I have in the past gotten into online arguments with people who claim that this kind of exponential change will continue forever, and I just find it so baffling. The only explanation I can come up with is that this is a core ideological precept of our current economic system and people are just not prepared to challenge it. Like asking a medieval person to believe that god is not real. It’s seen as blasphemy.

> We know this state of affairs cannot possibly last.

Talk for yourself. I personally think this is just the beginning.

Your freefalling similitude has the big flaw of making completely unsubstantiated assumptions. For all we know, we might be elegantly diving into a pool, or having propelled ourselves onto an orbit where we'll forever spin - we just don't know.

"just 12 light-years away"

I love the "just". I know it's nearby on galactic scales but it's practically about 450,000 Earth years away with current technology :-)

And "just" 24 years over radio if there's anyone there to talk with ;).

I doubt I'm alone in this, but I do find it simultaneously amusing and depressing how mind bogglingly big the universe (or even the galaxy) is. It's clear that discovering entirely new levels of physics will be necessary to stand a chance of going anywhere.

Or extreme life extension, or fully digital AI. Life span is a big part of the problem.

Personally I doubt that meat will go to the stars. Planets, sure, and maybe bases or settlements. The stars take too long.

You're not alone.

I grew up reading and watching a lot of sci-fi. Today I recognize that most of it was garbage in terms of physics, but I'm still saddened that the universe isn't that easy - we can't just hop on a space cruise ship and do a tour of a nearby nebula...

Going to Mars may be routine some day, though!

Just going to Mars will significantly increase your risk of cancer, unless we find smart ways to repair our genetic material as we go.

Well, for the journey itself the problem has a simple solution - more shielding. Then of course we have to answer the question of how can we get ships into orbit when they are full of shielding, but that's not insurmountable.

The bigger issue is actually living on mars - as romantic as that idea is, human habitation on the surface is really dumb, the radiation level is not insignificant, so anything long term would either have to be shielded or be under ground. And if we are going to build an underground colony....then why not start with one here on Earth?

Then of course we have to answer the question of how can we get ships into orbit when they are full of shielding, but that's not insurmountable.

If regular travel becomes a reality, you wouldn't shield the launch vehicle, but the cycler[1].

[1] https://en.wikipedia.org/wiki/Mars_cycler

The benefit of using a cycler rather than a ship that travels orbit-to-orbit is that there is no need to accelerate/decelerate the mass of the ship, just the perishables (people and provisions for the voyage)

You would accelerate a small vessel (like a crew dragon or orion), intercept and dock with the much larger cycler, then enter the ship for your x-month trip.

When you near mars, you get back into your dragon, and burn away from the cycler, entering into martian approach.

7 people in a Crew Dragon for 18-24 months would not be pleasant. 7 people in a flying space hotel would be far nicer.

You could presumably look at using a small asteroid to provide the bulk of the "cycler", offering plenty of shielding for the trip, you'd only have to get it into position once - far less fuel requirement.

My understanding though is Musk is planning on using BFR to go surface-to-surface, with maybe a refuel in earth orbit. I believe this is because of the amount of material that needs transporting to Mars for the first 20 years or so, and that mass can be used as useful shielding. Even if Mars becomes self sustaining and doesn't require a large amount of cargo:people ratio, I believe Musk is aiming for a much shorter transit time than 2 years.

> You could presumably look at using a small asteroid to provide the bulk of the "cycler", offering plenty of shielding for the trip, you'd only have to get it into position once - far less fuel requirement.

Or maybe even something like, as some have suggested (not me!), Phobos:

http://enterprisemission.com/Phobos.html

Warning: it's kind of out there. At the very least, it's perhaps interesting as speculative sci-fi.

Grand theft moon? That's as crazy as Space 1999.

Not as crazy as claiming Phobos is an alien spaceship though, with highly places ESA sources due to announce it soon (article date 2010)

> And if we are going to build an underground colony....then why not start with one here on Earth?

Because if an asteroid hits Earth or if the world superpowers decide to go full nuclear, the underground colony in Mars will survive (unless superpowers decide to nuke that from here as well...)

I'd argue that a colony at the bottom of our own ocean would survive literally any event of any magnitude, maybe except for a direct asteroid strike. In terms of survivability of the human race, that's a better project to start with - and of course then move on to other planets, but underwater/underground colonies would give us lots of insights into living in such environments permanently.

Fair point, but then we forgo learning how to build a rocket to leave this rock should there ever be a need.

Just....do both? Have a proper, city-size, self-sustaining colony on the bottom of the ocean, and at the same time keep developing rockets and vehicles to bring as much material and and many robots over to Mars as physically possible. Like, I don't think getting to Mars is an issue - we probably could send and even land someone on Mars within a couple years if we absolutely had to. But then the question is - what then? That's the hard problem.

The pressure range range between vacuum, mars atmosphere and earth atmosphere is 10⁵Pa. The pressure at the bottom of the ocean is 10⁸Pa. Humans can survive the former with little more than strong tensile garment and a breathing apparatus, the latter requires massive, crumple-resistant pressure vessels around everything.

Finally someone with the sense to realize what difference an order of magnitude can make to a decision. Now lets compute how likely we are to die by an asteroid vs how likely we are to die being stranded on a barren, frozen rock 60M Km away from the nearest source of critical supplies.

That depends on your time horizon. Probabilities of catastrophic events tend towards 1.0 individually. But within the same time horizon you can keep it close to 0 with sufficient redundancy and recovery.

So the tradeoff would be risking a finite amount of human lives in the short term to reduce the risk of a total loss in the long term. I.e. over time it becomes fixed vs. fractional cost.

The good thing is that Mars is chock full of dormant lava tubes[1]. That provides a solution to the problem you propose assuming we figure out how to seal them and make them habitable for human life. It is an exceptionally difficult, but tractable problem. FTL travel however, is not tractable at all with our current tech and (lack of) understanding of physics.

[1] https://en.wikipedia.org/wiki/Martian_lava_tube

you are not alone

Count your blessings. The vast separation between stars means that star systems can have stable planetary orbits for billions of years, which is important for life to develop.

I've read that most of Lovecraft's is derived from the horror at realizing how insanely large in both space and time the universe is.

The unspeakable horrors and mind defying deities in his oeuvre are effectively just reiteration of the "the human race is an irrelevant blip on the universe's radar" concept.

Well that just cries out for a quote :)

"We live on a placid island of ignorance in the midst of black seas of infinity, and it was not meant that we should voyage far. The sciences, each straining in its own direction, have hitherto harmed us little; but some day the piecing together of dissociated knowledge will open up such terrifying vistas of reality, and of our frightful position therein, that we shall either go mad from the revelation or flee from the deadly light into the peace and safety of a new dark age." - H.P. Lovecraft "The Call of Cthulhu"

beautiful, thank you!

Or entirely new levels of lifespan. Just upload yourself to the grid and boot up in a few million years.

Why 24 years? Radio travels at the speed of light, not half the speed of light, right?

Roundtrip time.

HAHA! Thanks, sometimes I need a kick in the rear. I was thinking one way.

Any response would take 12 years as well.

To me this sounds feasible.

We already organize space missions over the 20 year mark. Communicating effectively with another civilization could be taken just as seriously and done in an organized and effective manner.

It would take a while to get going but once the sharing starts it would be immensely productive.

> I know it's nearby on galactic scales but it's practically about 450,000 Earth years away with current technology :-)

If we had the political will, the Orion design could get people there in, what, 200 years, and that's with '70s technology.

Are you talking about the propulsion system where a series of nuclear explosions push the vessel along?

https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...

yes, we should explore (and eventually exploit) all forms of propulsion and decide between them based on physics, not politics

That Orion project was a failure though. No tangible results to exploit.

my point is that because of fear of nuclear no further research was done. It is now super hard to even get enough material for a rector/battery such as the one on Curiosity

I think it more just ended than failed.

Imagine being the child born on the ship on a crash course to this new planet.

And imagine you're the first ship to arrive only to find out

a) that the planet is not habitable and there were some wrong assumptions about it

b) that the planet is already occupied by a different form of life and there's no warm welcome to us

Sounds like the premise of Aurora! Which definitely turned me off the idea of multi generational starship travel. It's not ethical.

This is also assuming

A) Human engineering can create something that can last 200+ years of space travel. We don't even build houses anymore that can feasibly last 100 years.

2) People don't go mad and kill each other or do a mutiny

III) Any number of stray objects from asteroids to rogue planets that just slams into the ship and causes major malfunctions

d) Food and life support sustainability

I mean... there are SOOOOOOOO many more problems than actual politics. This is where, and it hurts me to say this, the politicians are right to say "are you insane?".

Of course we’re far from it, if ever possible. I was just being playful on the whole premise of “colonizing” another earthlike planet

Oh, I'm not bashing you at all. You're absolutely correct. You bring up extremely important things to realize when discussing space travel. Especially long term missions. Political will being the reason why these missions haven't happened, as someone else mentioned, is total crap. It's just an easy excuse to not think of ACTUAL consequences and live in a scifi fantasy.

Yes I agree, we seem to be working on the wrong problems or get the priorities wrong. We keep on inventing newer technologies which come with newer problems while the ship is slowly but surely sinking. Sometimes I wonder what would it take for all of us to join a concerted effort to concentrate on the real problems we have. Technologies seem to veer into an escapist route, some way for us to run away from the problems we do have: virtual reality, leisure space travel, AGI, synthetic life, immortality.. I hope we'll eventually wake up in the last hour, at least to acknowledge where we've gone wrong.

I think this is exactly why there's an apocalypse fantasy/fetish. It's in our psyche that we're all focused on... well... dumb shit. A post-apocalypse lifestyle makes you focus on what I think we can all truly appreciate as important. There's a lot of interesting studies done on localized disasters where the idea of community actually erupts out of it. People working together and sharing, regardless of their "social status". It's all short lived until the outside world aid arrives and you still get a few bad actors in the mix (though it seems statistically, no where near as many as we think). Generally though, it takes hell on Earth for us to regain our "humanity".

Not trying to be edgy, but I think a lot of society problems stem from more and more globalization. When you're less than a drop in a gigantic pool of people, it's hard to feel like anything matters. Not saying the closed off, nationalism system is any better in the long term. It's just hard to determine a balance to the system. And with that lack of balance, we run away into the escapes you mentioned.

Sigh... well, I just ruined my day thinking about this crap again.

I have a similar experience from my childhood. I grew up under communism in eastern europe and I remember the crisis we were going through at the time, food was rationed and there were long queues everywhere. People were even joining queues without knowing what was being sold and some would start lining up overnight. I was a kid back then and didn't experience the adversity first hand but I could see and sense what was going on. Aside from these things, however, I remember how helpful and inclusive the community was. People were sharing whatever they had, whatever they cooked, recipes, anti-establishment jokes, books, video tapes, etc. There was this sense of belonging that now has dissipated completely. I was struck with a deja vu when I visited Cuba a couple of years ago. People are poor but are sane and happy in their own ways and they have time for one another. There are still disparities but not like in a western society when one counts their pennies and the other their billions. Romania, the country I grew up in, has been engulfed in corruption and asides from a cities with large concentration of wealth, everything is in disrepair, the community disappeared almost completely and everything seems to have gone downhill for the past 30 years. In no way am I decrying the communism, it was brutal to many, but what has ensued after the fact was a veneer of shiny nothing.

So, I was born in the USA, but my parents are from Poland and left a few years before the collapse. They shared many similar stories with me over the years. Generally, when the environment is bad, the local people are good. But the reverse is true too. When the environment is good, people tend to suck.

It's weird to be honest. A lot of books/movies think utopia arises in the land of plenty. But I guess a real utopia is where we all suffer against a common threat/enemy. That's when we're most human?

But when it comes to communism, it does have it's upsides. Like now in Venezuela, almost everyone is equally poor as shit. Thus, criminals don't rob people. Bullets cost too much money compared to how much they can rob from people, if they even have anything. That's a win... I guess. Great way to stomp out crime. Make everyone too poor to even bother robbing.

Meh. 200 years aro they would have called you insane for wanting to fly between continents, let alone to the moon.

They also would have called you crazy for saying you wanted to turn lead into gold with alchemy. Fact is, most of the time the people who say something can't be done are right.

Yeah but they don't matter. All the trying was worth it, because I can fly halfway around the Earth for a few hundred bucks now. If in a different world I got gold out of lead but no airplanes, it would be fun too, but in a different way.

If the no-sayers really won and nobody tried, we would have neither.

> They also would have called you crazy for saying you wanted to turn lead into gold with alchemy.

Which is doable but exceptionally expensive.

Not a strong argument against the ship unless you're calling it a waste of money.

Nitpick: we can actually transmute, either by fusion or fission. Sure it's not economically effective, but then neither was Apollo.

The crazy ones are the ones that change the world/universe. For the right price, it would make sense to invest in such a venture.

> d) Food and life support sustainability

Could we just send frozen embryos of humans and then have the ship auto thaw and gestate them 16 years to arrival?

With another 2-300 years of technological progress this doesn’t seem outlandish mission at all.

that sounds highly unethical. none of those people agreed to go on the trip

did any of us agree to go on our current trip? I do see your point but I think eventually humans might do it.

Man, B is a good problem to have.

Imagine being the child born on a small island, or in a country to which few other countries are willing to grant visas, or simply to parents who don't have much money.

Imagine being the child born on the ship on a crash course to this new planet.

Here's one for you. What if WE are the children currently on a 'ship' (Earth) being sent somewhere..? ;-)

> If we had the political will

It takes more than that. We need political maturity and stability. There is no way we can send people today on a 200 years journey and be sure they will both make it and be able to create a somewhat stable society on the other side.

Also, that would be a earth level effort, another thing that is seriously irrealistic right now. The very best we can achieve right now is the ISS and that's pathetic even compared to current tech.

The biggest push in recent years has been around privatisation of space exploration. It is going to take decades, probably centuries before a commercial model of space settles down and non-profit utopist project like that would be conceivable.

Would a vessel from 50 years from now beat the original crew there? If we assume we are advancing speed-wise by X% each year, the poor folks sent and likely put into cryo-stasis would get lapped by people who left 10 years or 25 years after them.

There are a number of SF stories where this is the plot.

Imagine waking up out of your cryo-stasis and seeing humans already living on the planet you were sent to colonize? That would be weird, to say the least.

I bet there's a science fiction novel about that

If there isn't someone should write it.

I have read one. Many years ago, don't remember much about it. But I'm pretty sure it also discussed how all of the "future folk" were disgusted with the smell of the ones that had been traveling in cryo for 200 years. Too much perfume/deodorant...they didn't like the flower smells anymore as I believe they had engineered themselves to not perspire any more.

You could get their corpses there, sure.

Just got to make sure we put on the side of the ship, "Greetings from Earth!"

"They sent us a space ship full of corpses?" "Must be an intergalactic message of war."

That's almost as bad as receiving an unlabeled box with a copy of Misery in it.

The Orion program had this potential on paper. Nuclear bomb propulsion is a complicated thing, but we don't understand if it's a feasible propulsion method in practice, like, at all.

Political will in this case brings us more understanding of the feasibility of this propulsion method, but it's way too big of a stretch that political will alone would get us to the nearest starts in 200 years.

Actually we do know it would work. The fundamental physics are sound.

A pusher plate can in fact transfer net positive momentum from a series of explosive shockwaves detonated aft of the pusher plate in the desired direction of travel. There’s plenty of video footage from the Hot Rod tests showing it working. https://youtu.be/Q8Sv5y6iHUM

The hot rod test article was actually donated to the national air and space museum unfortunately it is not currently on display. https://airandspace.si.edu/collection-objects/propulsion-tes...

And for the realities of scaling up from conventional explosives to nuclear detonations you can read a little more here http://www.spacedaily.com/news/nuclearspace-03h.html and http://www.projectrho.com/public_html/rocket/realdesigns2.ph... (scroll down till you get tot project Orion and they have a pretty good summary) And the Project Rho information has links to lots of the technical details and material as well if you want to learn a lot more.

The propulsion could work. What about sustaining life for 200 year biospehere without any external resources?

What about interstellar debris?

What about deceleration?

And that's just the feasibility of the colony ship, then there's colonization/terraforming, etc.

I'd be thrilled to see such an effort take shape, but to say "it would work" has marginal relevance to "the project is feasible".

If I remember it correctly, the fast project would make 4 light years in ~150 years. So that would be 450 years (probably less, because it's on constant acceleration).

> If I remember it correctly, the fast project would make 4 light years in ~150 years.

133, but that's getting there as a missile (one-way acceleration, no turnover and decel to relative rest.)

If you enjoy the idea of propelling space ships using nuclear explosions, look up nuclear salt-water rockets (NSWRs, or Zubrin Drives). The idea is to dump pipes full of sub-critical amounts of radioactive salts out engine, combining outside the ship in a continuous nuclear explosion.

> If we had the political will, the Orion design could get people there in, what, 200 years, and that's with '70s technology.

No,the version of Orion that is mostly an integration challenge over 1970s tech would take almost 7 times that long to get to Alpha Centauri as a missile (i.e., without turnover to decelerate to relative rest.)

The even more speculative version was estimated to cut that by a factor for ten to only 133 years, but that's still to a target 1/3 the distance of this one, and still without deceleration.

Look into Project Orion. With thermonuclear bombs you could hit 8% c, which would get you there in "only" 150-200 years including acceleration and deceleration time.

That is still beyond humans with present day life spans, but extend life span to ~1000 years or go full AI and you can totally ride the "devil's pogo stick" to stars <=20ly or so awat.

Fusion rockets would probably be better. I mention Orion because we sort of know how to build it today... at ludicrous cost. No new physics and not that much fundamentally new engineering is needed. Orion is a fabulous and quite valid counter to the folks that seem to like to repeat the canard that interstellar flight is impossible. Hard as hell, sure, but not impossible by any means.

To a fully Kardashev type I civilization it might be around Apollo moon shot difficulty.

Is that subjective time for the crew or objective time? Is there much of a difference at 8% c?

Little time dilation at 8%, so not a big difference.

Assuming 200 years for people on earth, the traveler would experience 199.4 years

https://www.wolframalpha.com/input/?i=time+dialation+at+0.08...

>Orion is a fabulous and quite valid counter to the folks that seem to like to repeat the canard that interstellar flight is impossible.

I’d never say it’s impossible, if we maintain a civilisation for long enough it might even be inevitable at least at a minimal level.

However, Daedalus/Orion is far from as straightforward as has been suggested by you and others. It’s based on projections of technology made in the 70s, not 70s technology. There are also formidable obstacles, such as obtaining enough Helium3. The authors suggested extracting it from the atmosphere of Jupiter or Uranus. That by itself would be as hard as building the vehicle itself, if not harder. I’d like to see a design for a Jupiter atmospheric scoop and return vehicle.

Also Daedalus couldn’t take people. Staggeringly huge as it was, it was a flyby mission with a 450 ton payload. If it was going to decelerate instead it’s payload was about the size of a washing machine.

Not Daedalus, Orion. It was a 1960s research project involving Freeman Dyson and others. Google it. There is a fantastic documentary that I think is on YouTube.

Orion is kind of shockingly practical. It was forgotten for some time as it was a military research project not NASA or academic.

Do you acknowledge the fact that interstellar travel entails more than just speeding up and slowing down? Because that's what Dyson would be telling you if he were here.

You need a nuclear-powered airtight bunker that can sustain dozens of people, but that's also buildable with 70s technology.

Once you have propulsion and a ship you're pretty well there.

One of the main unsolved problems is the electromagnetic shielding, both front and back (as you need to turn to decelerate). Even at 0.08c every speck of interstellar dust has enormous impact energy, far worse than the radiation of your own bombs. AFAIK this is unsolved.

follow-up: here is what wolfram alpha spits out for a 0.1 grams dust particle hitting you at 0.08c:

https://www.wolframalpha.com/input/?i=1%2F2+*+10%5E-4kg+*+(0...

it's 35% of the fission energy released by totally fissioning 1g of U-235!

i.e. I don't know whether this it's feasible to just have a heavy water & lead shield, as 0.1g is fairly optimistic to be the heaviest particle hitting you. Already at this size we're in range of tactical nuclear weapons.

You will essentially kill dozens of people once they hit an interstellar cloud with anything bigger than a sugar molecule at 2/5c.

Nuclear salt water rocket would likely be even faster, but unlike Orion is still just a paper concept at this time.

Do we actually have navigation technology to travel at 8% c without crashing into deadly space debris?

Or more general: Space travel isn't just about speed.

Space is called space for a reason. Even in real life asteroid rich orbits the odds of hitting something are very low. Pulp sci-fi asteroid fields like the ones depicted in Star Wars are just not a thing. Outside the inner solar system the odds of hitting anything are so low the risk doesn't really rank in comparison with things like major equipment failure in transit.

I smiled as well but with a slowly but steadily accelerating ship we can reach half the light speed and get there in 50 years. It put things in the realm of "possible" which is amazing.

now do some napkin math on the reaction mass and energy you need to slowly accelerate that much for that long

And the energy transferred by an impact with a piece of dust at luminal speeds

Now do some napkin math on the amount of gears and levers you need to reach such calculating power, mr. Babbage.

don't forget, you're going to have to slow down at some point, too

https://en.wikipedia.org/wiki/Torchship

> Torchship (or torch ship) is a term used by Robert A. Heinlein in several of his science fiction novels and short stories to describe fictional rocket ships that can maintain high accelerations indefinitely, thus approaching the speed of light. The term has subsequently been used by other authors to describe similar kinds of fictional spaceships.

I think current technology makes no sense when talking about interstellar travel.

I wonder how long it'd take, seen from the perspective of the ship, if we had an engine capable of delivering a constant 1g acceleration.

That's the way we'll want to travel, after all.

constant 1g acceleration gets you to speed of light pretty quickly (around 1 year), so still around 12 years.

If our current ideas about physics are correct, acceleration _never_ gets you to speed of light.

The faster you go, the higher your relativistic mass, so if you accelerate by constant force, the lower your acceleration. Conversely, to keep acceleration constant, you would need larger and larger forces, in the limit ‘infinite force’.

For more and better info, see https://en.wikipedia.org/wiki/Space_travel_using_constant_ac....

> The faster you go, the higher your relativistic mass, so if you accelerate by constant force, the lower your acceleration.

The Wikipedia article you linked to calls this (rightly) a "half-myth". It depends on your reference frame.

As far as I understand, viewed from Earth's reference frame, a spaceship accelerating by constant force will get heavier and heavier as it gets faster, and thus get less and less speed out of it, asymptotically approaching the speed of light but never exceeding it. Moreover, crucially, any pingbacks from clocks on the spaceship we observe will appear to be progressively going slower than they should. (Time dilation)

The spaceship's own reference frame will be a whole different story. If I understand correctly, it will perceive its own mass to be constant, the rest of the universe's relative speed to asymptotically approach the speed of light, but also the rest of the universe to get progressively squashed in the direction of travel (length contraction dual to time dilation), with the two effects multiplying up in such a fashion that the Newtonian relation between the integral of your acceleration and the time it takes to the destination seems to hold throughout.

In other words, for the spacefarer's schedule, it's as if the speed of light does not actually play a role: they can always accelerate more/go arbitrarily faster to get to their destination faster. However, from their point of view, it is as if the universe around them will deform in the process to accommodate this, and from the stationary observer's point of view, it is as if they are actually still moving slowly but tricking themselves into thinking otherwise by accelerating their passage of time.

Unfortunately, radiation from hitting hydrogen atoms in interstellar space starts to become deadly around 0.25c or so, IIRC.

No, it will be much less as seen from the ship.

Seen from Earth, it'll be around 13 years (takes a year to got close to c and another to decelerate - that is two years to travel roughly a lightyear, then 11 to travel 11).

Course, assuming you want to orbit your destination when you arrive ... at some point you'd need to turn that 1g in the opposite direction to decelerate. (And I'm mighty impressed by the energy source that provides two years of continuous thrust.)

Lot of details relevant to this question here: http://math.ucr.edu/home/baez/physics/Relativity/SR/Rocket/r...

By way of comparison the entire 'human'species is about that age. += 250-500k years depending on how you measure.

Honestly it's far far far better to focus on reaching superhuman intelligence and AGI and then just creating a Dyson sphere around our sun.

At that point we can try to figure out FTL travel...

This! If you look at all the life on Earth, humans are the only ones to have maximized brain functionality and evolved to change their surroundings on a global scale. We should continue focusing on superhuman intelligence and AGI which will solve problems that we cannot simply right now due to our evolutionary limit at this point in time.

No, it's 12 years away by radio wave, which means 24 years for a round trip communication.

Physical travel is out of scope, but we could share knowledge in the (extremely) unlikely case that we found intelligent life with radio technology.

If we were to realize Breakthrough Starshot, then it'd be right around the cusp of how long I'd think we could maintain institutional interest in it. 60 years to get there, 12 years to get the signals back, so 76 years. If you worked on it right out of college and longevity stays around where it is, you might live to see some pictures. You definitely could tell your grand kids about it though.

It seems technically possible, it is just a matter of paying for something like this and pinning hopes on the next generations to follow through with it and appreciate it. It seems like if we had that sort of will, climate change and some other issues would almost be non-issues.

let's see if someone will try to upsell the Musk

To give a sense of the scales involved - if the sun were an orange and the earth a grain of sand 6 meters away, this star would be a pea about 5000km away.

There would only be another 34 stars / fruit-and-veg within this 10000km wide sphere. It's pretty empty out there!

I’m amazed that the specks on the grain of sand can even be aware of the pea that’s 5000km away in the first place.

>450,000 Earth years away with current technology

With current tech spread thinly an alpha emitter like Po (2% mass ejected at 5% c) on the backplate and you’ll get 100km/s with 10% payload. Adding an electromagnetic “nozzle” to axially redirect sideway alphas would make it past 200km/s, ie. less then 20k years. Spread thinly enough for the decay leftover - Pb - to be ejected too and you can get to something like 600 km/s, just 6000 years.

there is an effort to put super mini spaceships on missions to other solar systems, and they would travel at something like 20% the speed of light. I think it works by having the probes be like the size of a cellphone or something, and being attached to a solar sail, then using an incredibly high powered laser to pump the solar sail full of energy to get it going so fast. I think if that architecture works they could reach ... proxima centauri? ... in something like 20 years.

just pointing that out to say that i think we have technology that would take less time than 450k years :)

However, a transmitter with enough power to signal earth would be too massive to get fast with a solar sail, given today's technology. Maybe a chipsat gets to 20% c, but no way a dish does.

Found the wiki page for the project: https://en.wikipedia.org/wiki/Breakthrough_Starshot

so it looks like they'd want to launch by 2036. In the 'technical challenges' section, it does mention that some technologies would have to be miniaturized sufficiently, but it doesnt really mention much about whether that technology has reached viable stages or not, or whether it's a realm they'd have to specifically research further.

So I guess maybe the technology doesn't exist today? Sounds like probably not, but maybe the near future -- or at least they expect it to exist by 2036.

It's worth noting this project has backing by some pretty influential folks, including Stephen Hawking when he was still alive.

What if the chipsat sends the signal to the chipsat behind it which sends the signal to the chipsat behind it which....

So that the signal can be relayed by a bunch of short range transmitters all the way back to earth

Probably requires a surprising amount of short range transmitters to be launched then. I wonder if a formula could be developed that relates the energy needed to place one large transceiver at a given distance versus the energy needed to place small transceivers all along that given distance.

Time for the travelers will go slower, for earth time will be 450k years but for travelers will be less.

Can someone explain this situation, what if the travelers reach almost speed light, they will reach on 12 years from earth perspective but for them how long will it take?

I believe the problem is that with current technology it isn't realistic to expect to accelerate continuously to a fraction of light speed where time dilation will be noticeable. We lack the ability to get a large enough amount of fuel off the planet and we obviously can't decelerate to harvest more fuel on the way there because then we lose the benefits of the continuous acceleration.

EDIT: I wonder how feasible it would be to gather a large enough store of fuel from asteroids or comets before even beginning acceleration. You'd likely have to do it both ways which may make it a one-way trip if the destination doesn't have the necessary resources.

The only way I'm aware of that we could power a long-running acceleration is via a nuclear-powered ion drive. But I don't believe the acceleration is great enough to make a dent in approaching the fraction of the speed of light we need for such a journey in a human lifetime.

Please someone correct me if I'm wrong. I'd love to be wrong.

And to think that there is likely an Easy Mode system out there.

A habitable planet on the low end of the mass spectrum needed for a stable atmosphere with other habitable planets in-system. And all that close to another star with habitable planets, possibly in the sub-lightyear range.

Basically everything ripe for a spacefaring civilization to grow without too much trouble and with plenty of motivation.

The Earth is hard to leave and everything else in our system is dead rocks with hellish environments as far as we know with the nearest alternative at least dozens of lightyears away

Maybe the Great Filter is real and screwing up a system is as easy as screwing up a planet ;)

...why the winky face?

Why not ? Maybe sentient / intelligent life is thriving everywhere but 99.9% of time, climate change or nuclear annihilation happens. Even in "easy mode" with several planets. I find it ironic and somehow poetic.

I believe (like many people) sentient/intelligent life to be intrinsically valuable, and the suffering or extinguishing of that life to be bad.

Our own species suffers and harms itself far too much already. I like to think that we're doing relatively well, solving problems and navigating bad Nash equilibria and local optimizations with social systems and technology to make the world a better place. In as little as the last century, we've made huge strides in solving problems of hunger, illness, education, freedom of expression, and more. Even with the huge efforts needed to escape our heavy planet's gravity well with chemical rockets, and the limited habitability of other planets in our system, we're exploring the possiblity of colonizing other planets.

To imagine that this is a hopeless fight, even at the best of odds - that sentient/intelligent life is not only unable to succeed but is actively continuously exterminating itself across the universe - is a ghastly, horrific, tragic nightmare.

Imagine an easy mode planet in a system with multiple habitable planets. Now that I've typed that I'm also considering how Mars would look from 12 light years away.

Is establishing a colony 12 light years away easier than transforming mars into a habitable planet?

Harder, I think. We have the technology to live on Mars (not to terraform it, just to survive on it). We have some ideas from physics about how to get to a planet 12 ly away, but not the technology. Nor, I would argue, do we have the social and political setup required for such a project, which would most likely take hundreds of years to get to a basic colony.

> We have the technology to live on Mars (not to terraform it, just to survive on it).

I'm not convinced this is true intergenerationally without a maternity ward in a centrifuge; the low gravity mouse embryo experiments don't look promising. Maybe 1/3rd earth gravity is enough, but I'm doubtful. If we're granting centrifugal habitats as something doable with current technology, an Orion/Daedalus style nuke-propelled spacecraft seems in the same ballpark. It's been sketched out and tested with models, it's clearly possible, but nobody has really made one yet and it's a hell of an engineering problem still.

We should be colonizing the moon first, then Phobos or Deimos. Then, once established, we can conquer the martian gravity well with local resources.

I like Musk's plan of using Mars as a fuel-planet, I just don't expect a self-sufficient colony for some time. Mars is like an oil rig or a mineshaft; no place for children.

In fact it's cold as hell.

And there's no one there to raise them if you did.

Phobos and Deimos are very, very tiny.

The diameter of the Moon is 2,160 miles. The diameter of Phobos is 14 miles. Deimos is 8 miles.

(For scale, Mars' diameter is 4,200 miles).

That is the point. It's easy to land and get off a tiny moon and there is material to make a habitat out of rather than sending it all from Earth.

mouse embyro zero-G experiments being referred to: https://www.wired.com/2009/08/spacebabies/

> Harder, I think. We have the technology to live on Mars (not to terraform it, just to survive on it).

There is a chance that nuking the polar caps would terraform Mars, I think we already have the technology for basic terraforming.

edit: wrong quote :/

On interstellar travel realities: http://www.antipope.org/charlie/blog-static/2007/06/the-high... - aka it’s not happening soon.

And for terraforming Mars, Isaac Arthur’s YouTube channel has many related videos, and he posits that by the time your civilisation could do it, it would be a wasteful use of Mars when it could be better disassembled and turned into O’Neill cylinders or something.

But coming over a crater or valley on Mars and transforming it into something habitable would be enormously easier than travelling 12 ly.

Or perhaps that’s ultra-hard mode. Multiple fantastically different independent intelligent species evolving on planets within shooting range of each other with basic industrial technology.

If you’ve ever played civilization, it is a helluva lot harder to get started in Europe than in North America.

You consider 12 light years to be within shooting range?

Good luck with that.

Well, that’s just a matter of time. But I was referring to the parent comment’s system.

It's also a matter of space. Maybe you are unfamiliar with the concept of space-time and what a light year really measures.

You misinterpreted the comment. They were discussing a single star system with multiple habitable planets.

If more than one planet in the system gave rise to an intelligent species that develops a civilization, things would likely get very interesting very quickly.

Not likely. Even traveling to a planet as "nearby" as Neptune by conventional means would take 12 years. Hardly within shooting range, and who knows whether our civilization will survive long enough for us to make it to even the edge of our solar system.

And the OP was referring to a nearby star system, within "sublight year" range. Even < 1 light year could mean very, very far away.

They are referring to a single system... Here is the quote:

>> And to think that there is likely an Easy Mode system out there.

>> A habitable planet on the low end of the mass spectrum needed for a stable atmosphere with other habitable planets in-system. And all that close to another star with habitable planets, possibly in the sub-lightyear range.

Yes, they mentioned another star system as an additional point, but that wasn't the main idea.

> Hardly within shooting range

Mars is only 6 months away. We have the technology today to launch boulders weighing hundreds of tons to Mars. Those make for pretty good weapons.

>We have the technology today to launch boulders weighing hundreds of tons to Mars.

You must be joking, or you are completely unaware of Tsiolkovsky's equation.

https://en.m.wikipedia.org/wiki/BFR_(rocket)

100+ tons to Mars. Doesn't require any major technological breakthroughs. It's just really big.

If you want a rocket that has already been built, the Saturn V could have launched a ~50 ton boulder to Mars. Not quite hundreds of tons, but that was also built 50 years ago.

If the Earth was suddenly facing interplanetary war with Mars, I imagine we would start building some very impressive rockets quite quickly. And they would all obey the rocket equation :)

BFR is unproven, no one knows whether it could take a payload of hundreds of tons.

But yeah, in theory you could just build a bigger rocket. But even going from 50 to 100 tons increases the size significantly, let alone going to hundreds of tons like you said. Maybe that's not possible with today's technology, multi stages and all.

From that distance, Venus and Mars both look potentially habitable.

"Habitable" in also relative to our Earthly form of life. There may be other architectures that prefer different temperatures and pressures, perhaps.

Or aren't primarily carbon based whatsoever.

I highly recommend the book The Equations of Life: How Physics Shapes Evolution[0] . While it's be foolhardy to rule out other dramatically different forms of life, there are only so many candidates in the periodic table and only so many of those in common concentrations throughout the universe. The universal laws of physics that continually converge on the same solutions on Earth, and the fact that life has apparently failed to succeed even on nearby planets (perhaps at all, and certainly not advanced life) with different conditions suggests that it's at least unlikely to find life thriving at far different temperatures (atoms just don't hold together or move enough) or bases (I wouldn't completely rule out silicon, either, but the author makes a good case that carbon is far more likely)

[0] https://www.amazon.com/Equations-Life-Physics-Shapes-Evoluti....

Why does life have to be chemical as we know it? Why can't a massive galactic-scale lifeform exist upon gravitational waves, radioactive particles, or even dark matter or things we don't know?

Life isn't something that's easy to define because literally everything exhibits patterns of life to some degree (in fact, you could definitely argue that the concept of life is an arbitrary, fictional distinction made to make our lives easier). For example, we find that cities, states, and empires look "alive" at a macroscopic level, with cars and roads forming the circulatory system to deliver much needed nutrients to far corners of the respective territories; we often give anthropomorphic characteristics to planets (Mother Earth) and stars.

When we search for life, we're probably looking for something very similar to us, something we can interact with and befriend.

The question is, what kind of life do we know how to recognize? What kind of life definitely is possible, and what kind is just speculation? In other words: where should we look first?

The answer is: carbon rich, watery life. Coming up with biosignatures for ourselves is hard enough, coming up with a biosignature for a galactic nebula is unbelievably harder because we have no examples. Extrapolating from one example is much easier than from nothing at all.

Evolution, because no other phenomenon can drive the required complexity to reach 'life'. Natural selection works by inheritance and mutation. Things that can create copies of themselves with mutations that allow selection to act on, this list is short.

Some of the qualities of life is that it needs to: (1) be able to grow, (2) be able to reproduce (3) have hereditary traits.

I'll grant that there are probably galactic-scale patterns of light and gravity. My guess is that the amount of noise would make it impossible for any "life" to form. The unspecified type of wave would have to have an ability to store information in such a way that it would change the behavior of the waves.

As a tangent, these requirements of life is what makes the RNA world hypothesis so compelling. RNA is able to both store information _and_ act as an enzyme. 2-fer!

I agree with your general idea, that perhaps life exists in non-chemical ways, but a galactic scale life form would be tricky for a ton of reasons - just one would be inter-organism communication.

The Milky Way is a pretty average galaxy and it's 100,000 light years in diameter. In humans, if inter-hemispheric signals takes 3ms you can achieve roughly 40hz "synchronic activity". Let's say (and this is a massive simplification) that the inverse of the maximum inter-brain delay is ten times the "clock speed" of the brain. That would give a human that lives 80 years over 100 billion clock cycles in a life, and a galactic brain that communicates at light speed (so 3e-13 hz "clock speed") only 9467 clock cycles in 1 billion years.

So one single human life would have ten million times more "clock cycles" than a billion years of this galactic life-form existing. Or, the galactic life form would have about 3 minutes and 55 seconds worth of "normal" human thought, from the moment it's born until one billion years later. I know human babies certainly don't do a lot in their first 3 minutes and 55 seconds.

Or, for a simpler example: say a massive star goes supernova at one end of the "brain", damaging it and requiring resources from the other side. It'll be a minimum of 200,000 years before that section gets repaired.

Also, from 12 ly away, I'm sure that Sol would appear to have at least 3 habitable planets (Venus, Earth, Mars).

Sol does have three habitable planets. Plus some moons, at a push.

Habitability isn't a Boolean. It's hugely dependent on history, context, and resources.

The more Boolean distinction doesn't have a name - but if it did, it would be something like Stable Evolutionary Potential.

Mars and Venus both fail on that. The moons fail on it now, but may pass when the Sun turns into a red giant.

The Earth has offered it for long time, with some uncertainty about the near future.

There's no reliable way to distinguish SEP at a distance. But noting that a star has planets in its habitable zone and making some estimate of how many planets in stable systems are likely to offer SEP is a decent start.

>The Earth has offered it for long time, with some uncertainty about the near future.

What uncertainty is that? Nuclear winter won't even wipe life off the planet.

How common are "life-friendly" planets (Let's say: on a ratio of Life-Friendly Planet:Non Life-Friendly Planet)? And is there any way to check if life-friendly planets contain life without actually going there?

A good question. No sarcasm, it depends on your definition of "life friendly". Right now, we can't see much more than an orbit and a mass for these things. (There's a spectrum on a few of them, but AIUI for most exoplanets we're still just getting them from star wobbles, which gives us only orbit and mass.) Combined with the stats for the stars themselves, we can say whether or not they could conceivably be in the "liquid water" zone.

But we can't say that they are definitely suitable for life. If Venus and Mars were found orbiting other stars, the press release would declare they could be "life-friendly"; if you squint a bit, both are at least on the edge of where you could get liquid water under the right circumstances. Being much closer to the real Venus and Mars, we know they are both not actually great candidates, because we can see the details that prevent them from being useful clearly.

So I'd say "life-friendly" is a continuum, and kinda relative to the amount of knowledge we have about the planet, which for most exoplanets right now, is very low, making the "life-friendly" bar correspondingly low.

Detecting life in general is impossible; we are fairly sure Earth has had life on it in the past that did not meaningfully change the spectrum of Earth. However, there are some signatures that would be very, very, very suggestive. From what I've gathered, Earth's atmosphere containing free oxygen isn't quite proof of life from a single snapshot, as there are conceivably processes that could produce it momentarily, but having oxygen in our atmosphere consistently for millenia and eons is difficult to explain with anything other than life.

There are plans for doing spectrography on the atmospheres of these planets. This would allow us to get a pretty good picture of the chemical composition. Biological life as we know it should leave a different footprint than a lifeless planet but in the end we can only extrapolate what we already know about life.

Yep! And more specifically, if we found a planet that had an atmosphere with O2 in it, that would be highly indicative of life. Although it's not the only option, O2 is pretty reactive, and you need a constant O2-producing force to maintain it. An O2-producing force would be something like plants or some life that is creating hydrocarbons from CO2 and H2O.

I don't know that exact ratio, but the number of stars that you can see that probably have planets in their "habitable zone" is pretty high... One in 5.

https://www.popsci.com/article/science/one-five-sun-stars-ha...

In our solar system, 2-3 of the 8-9 planets are in the "habitable zone". So let's just say it's maybe one in 20 or so.

Over the last two decades we’ve gone from not knowing if there were any planets in other solar systems to knowing that almost all of them have planets. We now know the second factor in the Drake equation is nearly 100%.

We don’t yet know the third factor yet, the percentage of planets capable of supporting life. But we do know about 22% of planets are small enough to possibly be rocky and are within the “habitable zone” of a star.

So a possible answer to your first question is that it’s likely 0-22% of stars have at least one planet capable of supporting life like that on Earth. This doesn’t say anything about moons or asteroids or the probability of life developing on a body that could support it.

I'm curious to know if Mars would be considered life-friendly from 12 light years away.

As other commenters have said, we don't have the tools to see that far yet, so it's only through a miracle of math, physics, and engineering that we can deduce the size, distance from the star, and atmospheric composition of exoplanets from variations in the brightness and color of a distant star over time. The James Webb telescope should help, but because of the nature of the technique our observations are constrained to solar systems that are perfectly aligned with ours, such that the planets pass directly in front of the star relative to the observer. It's possible that we can survey enough of those stars to get a rough idea of the ratio of life friendly planets, but we'll likely never know for sure. Maybe conditions for supporting life are correlated with alignment to the galactic plane!

I saw a study recently, unfortunately I can't locate it now.

It discussed the possibility of there having been past civilizations on Earth, hundreds of millions or even billions of years ago. The conclusion was that this can't be entirely ruled out. It noted how few actual fossil remains we have for what we know of dinosaurs, and that there's a lot of space left in those gaps for all the evidence to have been destroyed.

It's incredibly improbable. While much of the planet's surface is recycled constantly, there are also huge swaths of land that are billions of years old and haven't changed enough to hide evidence of complex society. Dinosaur fossils are rare, but not that rare. Tiny ones are abundant. If all life on earth ceased today, you could come back here in a billion years and find plenty of evidence everywhere. Maybe it's not 100% impossible, but it's so improbable that it belongs alongside other fringe theories.

I like to entertain a mad fringe theory that the K-Pg asteroid was a war weapon.

You might think no species would be insane enough to consider bombing its own planet to the point of extinction-level oblivion, but - that doesn't appear to be true.

> there are also huge swaths of land that are billions of years old and haven't changed enough to hide evidence of complex society

Do you have any examples? The article in the sibling comment to yours directly states that the oldest large-scale swath of land (in the Negev Desert) only dates to 1.8 million years.

That's the oldest surface land, but the oldest crust is 4.4 billion years in Australia, and there are other places with less-old-but-still-billions crust. Natural erosion in those areas exposes extensive history, and we can dig too.

[1]: https://news.nationalgeographic.com/news/2014/02/140224-olde...

Surface land (current or former) is the only really relevant source of potential evidence here, though (unless we're specifically looking for subterranean civilizations, or perhaps for remains of old mines or wells).

Surface land is a bit of a misnomer here. While the crust is 4.4B years old in Australia, that doesn't mean all 4.4B years are sub-surface. The top surface there is new, but there are exposed areas going back billions of years. This is how all fossils are found; the oldest surface is the 1.8M Negev desert, but we constantly find 300M year old dinosaurs sticking out of the sides of river valleys and other eroded areas. My point is that we'd also find evidence of a billion-year-old advanced civilization the same way, and that in Australia in particular, you can go all the way back to the formation of the planet.

Maybe it was this?

Gavin A. Schmidt, Adam Frank: The Silurian Hypothesis: Would it be possible to detect an industrial civilization in the geological record?, https://arxiv.org/abs/1804.03748

I found it through an article in The Atlantic that may or may not have been linked on HN recently.

https://www.theatlantic.com/science/archive/2018/04/are-we-e...

Yes, I believe that was it. Thanks!

Indeed, there was a discussion about this article, about a year ago. As a fan (and amateur writer) of science fiction, I greatly enjoyed learning about this hypothesis.

Was there a civilization on Earth before humans?

https://news.ycombinator.com/item?id=16837120

I am not a geologist, but it seems improbable for a technical civilization (like our current one) to not leave a global geological mark. For example, our use of fossil fuels changed global carbon isotope composition: our atmosphere now has less portion of C13, because photosynthesis favors the lighter C12 atoms, and all our fossil fuels ultimately derives from photosynthesis.[1]

The changed isotope ratio will be detectable in every carbon-containing sediment layer ever produced in our age. And this is just one example.

[1] https://skepticalscience.com/print.php?r=109

How long would a civilisation need to survive in order to leave a geological impression?

Look up the PETM (Paleocene Eocene Thermal Maximum), there's definitely a d13C signature there.

It's amazes me a little that we have as much from the dinosaurs as we do, considering how long ago they lived. For many of them it's less than 100x the time between us and them, to go back to the beginning of the entire universe.

Waiting for the moment where we actually find a habitable planet with intelligent life. Next thing you know, we'll be developing ways in order to communicate with them, not just observing them.

Stop teasing me, Universe - and show me the aliens already!

Just as long as the universe doesn't show us to the aliens, I'm on board.

Check out the Dyson Dilemma for a well-reasoned theory as to why it is a high probability that there is no space-faring intelligent life anywhere in our galaxy or even perhaps our super-cluster.

https://www.youtube.com/watch?v=QfuK8la0y6s

There are holes wide enough to fit a solar system through that argument. Reductio ad absurdum.

Here, I'll construct an argument in a similar form. People don't like mosquitos, for various reasons including that they transfer deadly diseases. Therefore the presence of mosquitos says there's a high probability that the planet isn't actually inhabited by us, because we would have killed them by now. After all, we have the technology.

Maybe, by the time we get around to wanting to construct a Dyson Sphere, we will have found a better alternative. Maybe they aren't a good idea for any number of reasons (if you need one, read the Cixin Liu "Dark Forest" series).

Any argument of the form "X is inevitable but hasn't occurred, therefore Y" first needs very strong proof of the inevitability of X.

To be honest, I've never really understood how a Dyson sphere would be superior to many nuclear fusion reactors that you can move around / turn off and on / build more of / etc

The sun is 99.9% of the mass in the solar system. Most of the rest of the mass is in Jupiter.

If you are ultimately bounded by energy requirements then solar is where most of the available energy is even if you literally cannibalize the gas giants.

In this case it’s highly unlikely that there out there, that close, existing simultaneous with us. 4 billion years ahead of us...they’re either long dead or non-existing.

4 billion years, eh? Just about the amount of time we've had life here. Maybe they already colonized us, and we're descended from them.

Unless they colonized us with panspermia it’s about as likely as “intelligent design” they surely put in a lot of work in hiding the fact that they came here including engineering 3 billion years of evolution.

While possible seems a bit inefficient.

Let's just say a part of Mass Effect is real and there are actually many civilizations right now. What are the chances that we could even know they exist with the current technology?

We need to discover the mass relays first. Or the Asari needs to find us.

De-icing Charon seems like an appropriate peace-time use of the world's nuclear arsenal :)

The universe may have...

https://www.nytimes.com/2019/05/26/us/politics/ufo-sightings...

There was a paper recently that argued that the habitable zone is smaller than anticipated because either the concentration of carbon dioxide will be too high (and thus toxic at least to life on Earth) or - for small stars like this - there will be (toxic) carbon monoxide in the atmosphere.

https://phys.org/news/2019-03-complex-life-require-narrow-ha... (good article with link to the paper)

Life on Earth lived in CO2-dominated atmosphere for 1.5B years. If anything, CO2-rich world which is not overrun by SO2 and chlorine and phosphoric anhydride and scorching heat, like Venus, is as "potentially life-supporting" as it gets, save for a world with actual oxygen-producing life like ours.

Life, uh, finds a way: http://www.bbc.com/earth/story/20170125-there-is-one-animal-...

I was under the impression that planets to be life-friendly have to be close to their red dwarf star to a point they'll be tidally locked (one side always light other night), meaning their atmosphere would freeze on the dark side and planet would end up without an atmostphere.

This was my first thought, too, when I saw the article.

But our thoughts about the effects of tidal lock on the emergence of life is little more than philosophy, having only one datapoint to extrapolate from, at that one not being tidal locked.

I think there are other loopholes. Imagine a Jupiter sized planet that had an Earth like moon. The Jupiter size planet would probably be tidally locked with the star, but the moon could be tidally locked with the planet, not the star. Given that, it would have quite a varied and complicated day/night cycle.

Interresting setup you mention there, the earth-like planets d/n cycle would indeed be very irregular i imagine, depending which orbital speed it would have.

Atmospheres are useful, but are they a requirement for calling a planet life-friendly? Life on earth first developed in liquid oceans, not in the atmosphere.

Wouldn't an ocean vaporise somewhat automatically to create an atmosphere of there wasn't one already?

I think so. I don't know of many liquids whose surface tension is strong enough to resist a vacuum. Also, I've never heard anyone propose mercury (the metal) as a particularly good substrate for life.

Well, there's the possibility of liquid water under icy moons.

Only if it's exposed to vacuum (or an atmosphere). It might be enclosed by ice or other (preferably but not nessesarily transparent) material.

Even if the ocean is exposed, we now have the time it takes for 1. the planet to become tidally locked due to tidal forces, 2. the atmosphere to be stripped away, 3. the ocean to evaporate. That might be plenty of time for higher lifeforms to develop.

This was indeed the prevailing wisdom for some time. However, more recent research is somewhat more optimistic. Even an atmosphere 10% as dense as that of earth can circulate heat to the dark side efficiently enough, given the right composition. The night side temperature could be within the parameters required to sustain some form of life.

Furthermore, tidal locking is dependent on oceans and atmosphere, and can take many billions of years to occur, or even never. Mercury has plenty of time to tidally lock but is in a 3:2 resonance with the sun. There are even other options; for example, moons of gas giants within the habitable zone would be tidally locked to their primary and thus have a day-night cycle.

"However, more recent research is somewhat more optimistic."

I am deeply skeptical of that "recent research", which AFAIK is "computer models, where we have zero capability to verify the computer models against even a single data point".

The incentives to keep kicking the computer model until it provides something publishable, with no countervailing force provided by real data to be explained by the model, are just too strong for me to take that too seriously.

Physics models are often checked against other models (which might have had some confirmation) in simple cases, and there are a lot of other sanity checks you can make on them to ensure they are providing reasonable results.

Obviously, one shouldn't blindly accept them without experimental confirmation, but one shouldn't also be wildly pessimistic in believing calculations grounded in three centuries worth of validated equations.

Yes, I'm sure the simulations don't have results like making these atmospheres suddenly collapse into black holes due to errors in the simulation or something. They'd notice.

But these atmospheres have to stable across cosmological scales in a highly iterative, chaotic environment. There is a mathematical lower bound on the rate such simulations must leak bits as a result of those things. I don't think we have enough bits of real information to make up for that, as it would take rather a lot.

Against the mathematical argument, I set the human argument that, like I said, there's all sorts of incentives to report the one simulation that produced the result that there may be an atmosphere and maybe it could even sustain life! That's a lot of high-profile articles and probably a promotion for getting my department some public attention. Even if hundreds of other simulations all result in "Yeah, the atmosphere freezes out".

Between the math saying we can't really expect this sort of simulation to contain meaningful information and the human factors involved, I can't put a lot of confidence in a model which can't be validated against real data.

I do find it amazing how people who probably think they're really in favor of science and support it will jump up to defend a methodology that literally runs off of zero data. Can someone explain the scientific process to me clearly that involves having no data at any point?

How did we verify the earlier theories?

We check them against data.

I have no objection to computer models; I object to computer models that can't be checked against data.

Cosmologists run a lot of models, to do things like try to determine the effects of dark matter on the universe. Such models are intrinsically problematic since they have to have resolution on the order of hundreds or thousands of lightyears on a side, or have to work with universes much smaller than the real one, or something that means the simulation is by necessity literally several dozen orders of magnitude smaller than the real universe (consider both the timestep and spatial dimensions).

But they can check the result by looking up in the sky and seeing if it matches. This allows them to overcome the problematic nature of the models and use them to say real things.

One wonders what exciting cosmological papers proposing all sorts of amazing and outlandish theories as a result of some computer model of the universe have been suppressed by the fact that they didn't correspond to the sky at all. I guarantee you that some very amazing simulations have been run that produced incredible results of great interest, whose only crime was that they completely failed to match the universe.

We don't have a tidally locked planet that has an active atmosphere in our solar system to look at.

well even our deep space observations are largely computed. nobody has "seen" these 2 planets at all ;)

what does seeing mean? does it have to involve photons? can gravity work as well? sensors and computation are always involved, nothing is directly seen.

Every new simulation is publishable. And every simulation that is more detailed than what came before will receive some attention after being published.

If physics has some bias they polish their models towards, it's on the direction of repeating the findings of the previous ones, not of changing them.

Or a day-night-day-penumbra-umbra-penumbra cycle. The primary-facing side would get maximum light just before entering the penumbra, experience total darkness in the umbra, and get some light directly from the star and some reflected from the primary from the time it exits the umbra to the time it re-enters. Every day would have a full stellar eclipse at noon. Every night would see the primary cycle from waxing half through full to waning half. The space-facing side would have an ordinary day-night cycle with the same period as its orbital period around its primary.

I always visualized that the tidal locking to be sort of like meshed gears, such that the one revolution around itself is same as a rotation around the star/planet if its a satellite.

But that shouldn't affect the day/night in this case right? Since we are talking about planets not satellites of planets and they are light sources not just reflecting light from the star. Can you please correct where I am wrong?

It follows from "one revolution around itself is same as a rotation around the star" that a planet tidally locked to its star presents the same face to the star at all times, so you have a 'Day' side and a 'Night' side. Neither side of which is likely to be particularly life friendly. Perhaps there might be some 'twilight zone' that could be though...

Tidal locking means that the denser side of the lighter body always faces the heavier body, and the less-dense side of the lighter body already faces away from the heavier one.

The moon is tidally locked to the Earth, which is why it has a dark side.

So the Apollo "earthrise" photos are just "earth"?

No; they weren't taken from the moon; they were taken from the Apollo 8 spacecraft, which was orbiting, so the Earth did in fact 'rise'.

Yes, Earth does not move significantly on the moon sky, if i remember right. It does rotate though.

Edit: Archgoon is right, the photos were taken from the orbiting module, so a rise happened.

There is no dark side in the moon.

There is a far side.

You're right, but I'm pretty sure that "The dark side of the Moon" is a proper name at this point.

It's dark like the darknet is dark... Occluded.

Such planets might also have moons.

Not ones with 1.1g!

Why not?

Because then it would be a double planet.

It depends on how big the "main" planet is, I guess. But I think we are running into definitional issues here, and it gets technical very fast. First, IAU does not recognize the term "double planet". Second, a body which is large enough to reach hydrostatic equilibrium (i.e. a sphere) but has not yet cleared its orbit is technically not a planet. So I don't know where this leaves us. A Jupiter-sized planet with an Earth-sized satellite would be such a huge mass and volume difference (an even bigger difference than the Earth and Moon) that it seems to odd to term that a "double planet".

TFA said the planets were rocky and 1.1g.

They could have a resonance orbit that would enable a (slow) day-night cycle. But some theories also suggest that M-class stars tend to flare for the regular radiation diet. Otherwise it would be awesome to have an M-class sun, since they can have lifespans multiple times longer than the current age of the universe.

I'm sorry, I'm not at all educated in this subject and I might be misunderstanding what you are saying, but isn't Earth the perfect example to argue against this? We're a life-friendly planet that isn't tidally locked?

I think this is just for red dwarf stars, not ones like sol.

It has to do with the class of star. This star is so cool that the only way for the planet to be warm enough to support life is for the planet to be really close to the star. I don't really understand tidal locking but I think it happens vastly faster at closer orbits - because there is a stronger gravitational gradiant closer to the parent body.

Tidal lock is caused by differential gravitational attraction. The half of the Earth currently facing the sun experiences more force pulling it towards the sun then the part facing away - which manifests as the spin of the planet having to do work against gravity to keep the spin going.

As a planet gets closer and closer to it's star, this gets more and more pronounced and all the various deformations and instabilities begin to favor braking the planet rather then it continuing to spin.

Feels like we're playing the first round in "Master of Orion" when you start scanning the stars around you ;)

I still love that game.

I remember around 2003, making huge battleships in that game and squaring up against the AI's armada. The AI made about 500 tiny ships with weapons incapable of breaching my shields, and with their own shields incapable of surviving my dreadnought blasts. I would kill 5 with my big ships, take no damage from 495 shots, rinse and repeat. The battles took hours! I had to skip tactical battles, couldn't stand that much time, just had the AI simulate it.

> The team calculates that one of the planets, called Teegarden’s star b, completed an orbit in a mere 4.9 Earth-days; the other world, Teegarden’s star c, has an orbit of just 11.4 days.

I wonder how our understanding of orbital mechanics would have evolved differently had our planet orbited the Sun this fast?

If the planets have long days, then they could potentially see in one night what it takes us a full year to see!

Just imagine the astrology columns in the local newspapers

I wonder how different this would make life. Would you experience seasons, or would the temperature be fairly consistent all year around as it wouldn't be long enough for the atmosphere to cool down.

"Seen here in an illustration"

This half-hearted attempt to say that the impressive-looking image of The Nearby Star was in fact an artist's impression of what a Red Dwarf might look like, made me laugh. Is it seen here? Or is it an illustration? I suspect someone changed the copy just before publishing

If you see a picture of the surface of a star that's not our sun, it's certainly an illustration. No such image exists of any other star.

Wouldn't planets orbiting this close to the star be tidally locked to it? If they are tidally locked to the star, they are also likely to have extreme temperature variations between the two sides. This could rule out life.

If that’s true, as it is true for planets in the TRAPPIST system, then at least there is a potential for life to develop around the thin longitudinal slices located more centrally, where climate may be more temperate.

Also see this comment below, something I wasn’t aware of: https://news.ycombinator.com/reply?id=20212953&goto=item%3Fi...

I’m curious- at the end of the article, one of the scientists remarks that the stars might be “zipping around” their host star faster than measurements predict, which could rule out potential for life. Is this referring to your suspicion re: proximity => tidal locking => extreme temperatures? Or is there some way that speed of orbit can affect potential for life?

As for interesting consequences of a vastly different planetary age: in one SF novel (could be Peter F. Hamilton's, I can't remember right now) humans colonized an Earth-like planet only some 2 billion years old or so. Its uranium ores had so high U235 content (as opposed to Earth's 0.72%, which requires costly enrichment), that you could simply smelt it and put straight in a reactor (cheap nuclear-powered locomotives anyone?).

By the time our technology reaches the point that we could feasibly travel to and inhabit another distant planet, and with all the challenges with that (space travel, terraforming, radiation protection), couldn't we feasibly create or move a planet or gigantic space station built from materials of another planet into whatever orbit we want?

Yes, possibly, but my curiosity about the natural life on those other planets outweighs that thought.

For those that wants to live on another planet, you will unlikely like how things look under another suns sunlight. It is hard to have a planet that will have day light like our sun and be habitable. Think of a yellow-reddish, or a light that is cold blue when you walk out. Human eyes evolved with earths lighting conditions.

You assume that any of us ever go outside to see the light on Earth, anyway.

If there is a Life friendly planet, which is much older than where we live, shouldn't there be life forms?

Shouldn't those be searching for other life supporting planets, vigorously than us since they would be much mature and advanced?

why no one found us?

WHAT IS THE PROBABILITY OF US FINDING AN ALIEN VS AN ADVANCED RACE FINDING US AS ALIEN?

"We can be either alone in the Universe, or not alone. Both possibilities are terrifying" (quoting from memory).

Well, I guess that is where the Fermi paradox comes in...

> Teegarden’s star is a stellar runt that’s barely 9 percent of the sun’s mass. It’s known as an ultra-cool M dwarf

Is it too late to change the name to Tyrion Lannister?

Tyrion Lannistar

What are the consequences of a star that mostly radiates infrared light for habitability? Would it restrict what kind of life could evolve there?

What I’m interested in is if somehow there is a planet almost exactly like earth, if so would they have evolved humans similar to us.

I too like this thought experiment! Checkout the movie Kpax with Kevin Spacey if you haven’t already, it touches on the subject — ”Why is a soap bubble round? It’s the most efficient form”

Assuming we have technology to reach a new planet 12 ly away, is going to a red dwarf star a good investment strategy?

If you have the money and technology to go, you’ll just hop to the next solar system

Perhaps habitable planets will be necessary for human migration and colonization, rather than finding aliens.

Is it possible to determine the atmospheric composition of these planets? How much water for example?

Why aren’t we discovered? Probably because an advanced civilization but barely reach for the first time would be wise not to fly in risk getting detected and captured. So they wait till they have overpowering cloaking ability before re attempting a sighting. Maybe by that time, we are no longer interesting because of their own advances

Also there is probably a super small probability where both civilizations are in similar advances that they can brave a encounter without worrying. If one is way more advanced, either one may not be interested, or the less advanced one chickens out/ gets destroyed because they want to hide their location.

I don't think there is redundancy in Universe

Do these planets have their own moons?

Moon-size objects are probably not detectable with current technology.

How do we check about life that far?

Only 70 trillion miles away...

Calling than A and B

"nearby"

Telephone Sanitizers and Hairdressers back your bags!

The trilogy _Three Body Problem_ is a good read, and has something to say about this. :)

I had high hopes, but TBP is a terrible novel. It certainly has some fascinating ideas, but just as many ludicrous ones that are equally central to the plot. Not to mention Liu is absolutely terrible at anything relating to characters: dialogue, character development, etc.

Reading that someone else had this opinion of TBP is so valididating. The book receives much hype but the characters are weak and forgettable.

Not that I want to pile on, but I didn't make it past 100 pages. It's badly written, and I don't want to waste my time when I could be reading something else.

I agree - I read the trilogy and enjoyed it somewhat but I wouldn't recommend it to others (unlike e.g. Hyperion Cantos or Fire Upon the Deep, etc).
The amount of suspension of disbelief for some questionable premises is very high. e.g. the real-time comms developed by one of the races breaks down one of the key axioms.

I read TBP and A Deepness in the Sky at the same time. Despite the "big ideas", TBP isn't even in the same league. Can't bring myself to read the second TBP book, just don't care. Did buy a Fire Upon a Deep recently, looking forward to it.

A Fire Upon the Deep is SUCH a good book. I loved it; the idea that something like the '90s net news had gone galaxy-wide was a great plot idea....

The first chapter itself was gripping. I was like, if this book is 1/10 as good as the first chapter, I'm sold. It's now one of the books I recommend to teen scifi readers.

Vinge is a master.
"Rainbows End" is must-read cyberpunk IMO. (And of course he wrote "True Names". (In '81!))

Yeah. Having read all three, they were interesting but not anything I'd re-read.
The opening of TBP had me hoping -- being a big Neal Stephenson fan -- that the whole book would involve a lot more of the historical context of the early PRC, and then it all went somewhere completely different. I strongly feel that the first bit of the book set in the past is the best part of the entire trilogy.
The idea of Chinese sci-fi in general becoming a thing is very cool though, I think.

> historical context of the early PRC
I mean, China has censors. I get the feeling it had to be a somewhat veiled metaphor, although it felt extremely obvious too.

Over in the s-f subreddits, this novel gets so much love. So I feel left out that I - like you few here - really hated it.
My big thing was that the science is just wrong.
Most fundamentally, it's not a three-body problem, there are (at least) four bodies: the three suns and the planet.
And the real world isn't going to follow any theoretical solution to TBP anyway. There is atmospheric drag, microscopic gravitational perturbations from the rest of the universe, decreasing solar masses as the stars age, and so forth.
In a system as chaotic as was described, any of these things make the problem intractable.
That said, I did enjoy the description of a digital computer implemented with "people" acting as the logic gates.

I don't understand your opposition to the name. The three body problem is so named precisely because it's intractable. In physics with two bodies you can perfectly model the evolution of a system, but as soon as you add a third it becomes chaotic and requires numerical simulation to approximate solutions.

I don't understand your opposition to the name. The three body problem is so named
Look at my first objection, that the problem described in the book has (at least) FOUR bodies. Yet the idea that it's a three-body problem is pervasive throughout the book.
Surely that in itself is enough to justify some aggravation.

I was just debating about this book and read some not so favorable goodreads reviews about it. Can anyone recommend something similar to 2001 oddysey (the book) specially the part about going through the stargate?

The concept of the dark forest is pretty interesting for sure.
Do we really want to be announcing to the galaxy our presence where malevolent alien species may be present. If they have developed technologically even just a couple hundred or couple thousand years ahead of us we'd be easy pickings.

Greg Bear's The Forge of God explores exactly this issue, as does the sequel Anvil of Stars.

I was just debating about this book and read not so favorable reviews about it. can anyone recommend something similar to 2001 oddysey (book) specially the past about going through the stargate?

We detached this subthread from https://news.ycombinator.com/item?id=20214062.

How long will it take until the next planet is overpopulated and resources are consumed?
I mean: birth control? Socialism? Rules to obey?
If it is a competitive race it will end up pretty much the same. The question is then only: how long will it take?
Over to the next one ...

You got me. I'm from one of those planets.
A group of us decided to move to earth for the warmer weather. It's also why most of us live in California and Florida.
Tan Mom is our leader.

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