Kepler telescope glimpses population of free-floating planets | Hacker News Reader

Kepler telescope glimpses population of free-floating planets

phys.org

211 pointsjaytaylor98 comments

This is expected to be the ultimate fate of the gas giants (Jupiter, Saturn, Uranus, and Neptune) after the Sun leaves the main sequence in about 5 billion years. Within 30 billion years of the Sun becoming a red giant, Jupiter and Saturn are predicted to fall into a 5:2 orbital resonance that destabilizes the system, eventually causing all but 1 planet to be ejected within 30 billion years. The remaining planet is expected to be ejected within another 50 billion or so years.[0]

So, within about 100 billion years, all that's going to be left of our solar system is a white dwarf (which will likely survive for trillions of years[1]), and 4 rogue planets, each drifting alone in space.

Somehow, I think this little story is more interesting than the posted article, perhaps because it literally hits home.

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[0]: https://arxiv.org/pdf/2009.07296.pdf

[1]: https://en.wikipedia.org/wiki/White_dwarf#Fate

Assuming the gas giants remain roughly the same as they are now, what would happen to them as they left the solar system and the heat of the sun? Would the gases condense down turning them from gas giants into rocky planets?

Eventually, but it would take much, much longer than you'd think.

Jupiter, Saturn and Neptune all radiate ~2x the heat they receive from the Sun. Most of their heat is primordial, residue from the gravitational potential energy of all their component parts falling together. A gas giant flung away from it's host star will likely remain more or less as it is much longer than the star is.

> Jupiter, Saturn and Neptune all radiate ~2x the heat they receive from the Sun.

As I've said elsewhere, this is most surprising for Neptune, but the fact that these bodies radiate this much heat is a clue that something more is going on.

The primordial heat hypothesis doesn't hold up, as Uranus was formed around the same time as Neptune and its energy balance is 1.05. If the comparison is indeed accurate, then the question remains what is making these planetary bodies so hot? Neptune especially.

Here are the energy balances of each to our best estimates,

Jupiter, 2.132 ± 0.051 [current estimate, older estimate was, 1.668 ± 0.085] (source, https://www.nature.com/articles/s41467-018-06107-2#Sec2)

Saturn, 1.78 ± 0.09 (source, https://www.sciencedirect.com/science/article/abs/pii/001910... )

Neptune 2.61 ± 0.28 (source, https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/91JA... )

My tweets on the topic, https://twitter.com/_areoform/status/1373376028861734918

> as Uranus was formed around the same time as Neptune

[citation needed]

There is clearly an unexplained anomaly vis-a-vis Uranus and the other giant planets. But the closer you look at them, the more weird Uranus appears. It would be amazing if it turned out to be a much older planet captured by our solar system. (That would certainly explain the weirdo rotation...)

Here you go!

https://books.google.com/books?id=RaJdy3_VINQC&pg=PA224&lpg=...

https://iopscience.iop.org/article/10.1088/0004-637X/789/1/6...

http://www.psrd.hawaii.edu/Aug01/bombardment.html

For me the anomaly is the heat of these planets, and the physical processes this suggests. I suspect that our current explanations are only partial and that a great discovery lies somewhere here.

Uranus got knocked over by getting hit really hard, a bunch of times: https://www.space.com/13231-planet-uranus-knocked-sideways-i...

Do we know if any exoplanet gas giants are similar in this regard?

If an observer from a distant star, say any of the stars we've discovered planets around, were observing our solar system, would the gas giants stand out because of this, or are they still too close as to be out-shone by Sol?

Just to add on to this, NASA estimates that the internal core temperature of Jupiter could be as hot as 24,000°K [0]. For reference, the Sun's photosphere has a temperature of about 6000°K [1].

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[0]: https://www.nasa.gov/audience/forstudents/5-8/features/nasa-...

[1]: https://www.scientificamerican.com/article/i-read-that-the-s...

>the Sun's photosphere has a temperature of about 6000°

There was a paper that proposed that Earth's surface was about this hot for a while after the collision that formed the Moon.

Even though the heat wasn't coming from nuclear fusion, for a while it was just as hot as a star, so the Moon, which was smaller and cooled faster overall, was remelted in places by "Earthshine" - therefore the discrepancy between the maria on the near side and the far side.

For reference the temperature at the center of the sun is about 15 million °K

Please forgive me, I am not a cosmologist, merely a humble software engineer - but your timespans of 30+ billion and into “trillions” of years seem awfully askew. The age if the entire universe is estimated at “only” 13.77 billion years old, so how is this possible? Are we simply in an extremely young universe?

> Are we simply in an extremely young universe?

Well, in the set of positive reals, any number you randomly pick will be very small compared to the vast majority of all the numbers in the set.

Yeah because the age of the universe can't be negative.

Yes, by our current cosmological models, we are in a very young universe.

We don't really know, but it may be the case that the universe is only conducive to life during this phase of its existence.

From my understanding the universe is but a toddler - the longest stretch of its life will be AFTER the last stars have died - this video is somewhat existential dread inducing https://www.youtube.com/watch?v=uD4izuDMUQA

See also: it's quite likely that no red dwarf anywhere in existence has run out of fuel, yet - some are estimated to last as long as 10 trillion years.

I find the concept of a black dwarf to be fascinating. Like you said - none have existed yet, and any absorption of matter as it floats through space will prolong its radiant heat.

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

Okay, so as long as you have 3 or more bodies, I understand ejection. Energy gets transferred semi-randomly such that eventually one body gains too much energy and shoots out.

But when N=2, what is the ejection mechanism? That's an elliptical orbit that should be spinning round and round forever (sans the losses via gravitational waves).

You mean how does the last planet get ejected? Well, that's an interesting question, actually. Because of the inherent stability of the 2 body system, the last planet gets ejected some ~50 billion years after the others.

The authors' simulation takes into account the fact that a star comes close enough to the Solar System to have some tangible effect every 23M years or so. It's the cumulative effect of these stellar flybys that eventually nudges the last planet out of the system.

Ok, external perturbation, got it.

Yeah, that makes sense. Otherwise it would just very slowly spiral in, due to losses from general relativity.

Yep, and loss of angular momentum due to it being carried away by gravity waves would probably take many trillions of years, I would guess.

> the fact that a star comes close enough to the Solar System to have some tangible effect every 23M years or so

Do you have a good source that expands on this? That sounds so interesting.

Understanding there's orders of magnitude of possible scale, what's the likelihood that one of these passing through the solar system would destabilize it enough to affect Earth? What happens if it hits the sun?

Very low but a more common and likely possibility is that it could disturb the oort cloud and cause comets to fall in system. Guess that could classify as what you are referring to depending on your definition of solar system.

A passing star is more likely to do this though and we believe that they indeed have caused disturbances in our oort cloud in the past. They might be potentially less numerous than rogue planets as our universe ages but they have a far larger potential hill sphere than even a very large planet so interactions with neighboring stars' hill spheres are more likely and frequent.

I've normally seen "oort" capitalized, so here is some background if others have the same question as me.

The Oort cloud (/ɔːrt, ʊərt/),[1] sometimes called the Öpik–Oort cloud,[2] first described in 1950 by Dutch astronomer Jan Oort,[3] is a theoretical[4] concept of a cloud of predominantly icy planetesimals proposed to surround the Sun at distances ranging from 2,000 to 200,000 au (0.03 to 3.2 light-years).[note 1][5] It is divided into two regions: a disc-shaped inner Oort cloud (or Hills cloud) and a spherical outer Oort cloud. Both regions lie beyond the heliosphere and in interstellar space.[5][6] The Kuiper belt and the scattered disc, the other two reservoirs of trans-Neptunian objects, are less than one thousandth as far from the Sun as the Oort cloud.

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

It was not very long ago that I realized the outer bounds of our Oort cloud are actually closer to Alpha Centauri (4.25 light years away) than the sun.

The scale of the universe never ceases to elicit feelings of existential dread.

The outer edges of the cloud seem to be at ~100K AU [0], while the α Centauri system is ~268K AU from us [1]. NASA also gives the same number [2] for the distance to the edge of the cloud. So, it looks like the Cloud extends almost halfway to α Centauri, but not that it's "closer to α Centauri than us").

As for the scale of the Universe: https://htwins.net/scale2/

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[0]: https://en.wikipedia.org/wiki/Oort_cloud#/media/File:PIA1704...

[1]: https://imagine.gsfc.nasa.gov/features/cosmic/nearest_star_i...

[2]: https://solarsystem.nasa.gov/solar-system/oort-cloud/overvie...

Huh, the first paragraph of that same wikipedia says the cloud extends to 2000 AU.

Either way, whenever I try to think about these things, I feel mild anxiety. Why am I here? What's the point of all this? I'M SO TINY! Aaaahhhhhhhhh! I probably need to lay off the sci-fi novels for a while.

This sounds reasonable to me, assuming Mercury didn't either fall into the Sun or hit Venus. However, from the perspective of Earth, we might not notice this much, due to the effect of Jupiter (usually) either flinging comets away from us, or actually absorbing the impact of the comets.

Ejection of the gas giants doesn't even take place until after the Sun has gone into its red giant phase. The Sun will swell so much that it engulfs the inner planets (Mercury, Venus, Earth, Mars), so, Earth won't even be around to become destabilized.

Interestingly, the paper I linked talks about Mercury having a 1% chance of becoming unstable before the Sun enters its red giant phase:

> The mechanism forthe onset of Mercury’s instability is well understood: by virtue of locking into a linear secular resonance with theg5mode of the solar system’s secular solution, Mercury’s eccentricity can attain near-unity values, resulting in a collision with the Sun, or even Venus. Intriguingly, General Relativistic effects factor into this estimate, with ancillary apsidal precession providing a stabilizing influence on Mercury’s orbit.

If Mercury collides with the Sun, not much interesting will happen. Mercury doesn't have enough mass to disrupt the center of gravity of the Solar System when it falls into the Sun, so, all that will happen is that the planet will get vaporized, and the Sun will become infinitesimally more enriched in metals. If you were around to witness the event, it might be visually spectacular, but not particularly significant with respect to the fate of the system itself.

They go on to say:

> Within the context of this narrative, however, the remaining planets appear unaffected and are currently expected to remain stable for a lower limit of 10^18 years, when diffusion arising from the overlapping mean motion resonance of Jupiter and Saturn are expected to decouple Uranus.

This analysis, however, is reflective of older studies, which don't take into account certain factors that this paper does.

If Mercury collides with the Sun, not much interesting will happen.

Yeah...but if it hits Venus......

Would time even make any sense given that we use the very system to measure time.

In the sense that one second is 9,192,631,770 transitions between two energy levels of the caesium-133 atom, no, there's no change. 50 billion years is just shorthand for a multiple of this number of transitions. International Atomic Time, or TAI, is precisely defined for this kind of measurement.

Whether TAI is a fixed number of leap seconds away - potentially billions - from UTC, is another question entirely. If 'one day' is one rotation of the planet Earth around its axis, and 'one year' is one rotation around the Sun, and hours, minutes, and seconds are fractions of these rotations, yeah, those cease to have much meaning when the planet is swallowed up by and dissolved into the Red Giant Sun's expanding chromosphere.

Yes:

> The second is defined as being equal to the time duration of 9,19,26,31,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the fundamental unperturbed ground-state of the caesium-133 atom.

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

Unless the laws of physics aren't constant over very long time periods for some reason, we could (if we were around to do it) measure time 10^18 years from now just the same as we do today.

In Oklo, Gabon there was a natural nuclear fission reactor about 1.7 billion years ago. The concentration of uranium and groundwater was just right that nuclear fission occurred naturally.

We can measure the elements left behind and we have determined that the fine structure constant was the same then as it is now.

If the laws of physics have remained constant for that long then most scientists think they will remain constant in the future.

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

Oh, sure, I wasn't saying the laws of physics were likely to change, simply that if they did, the SI definition of time might not be well posed.

That said, although I agree the laws of physics are likely to remain constant, 1.7 billion years is only just about 12% of the age of the Universe. And, that time period only reflects the most recent 1.7 billion years. So, there's still some theoretical wiggle room there for the fine structure constant to vary over time. After all, heat death is not expected to occur for much more 100 trillion years (if that is our ultimate fate)! [0]

Edit: Come to think of it, if the laws of physics aren't constant, how would it be possible to pose a coherent definition of a unit of time at all?

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[0]: https://en.wikipedia.org/wiki/Future_of_an_expanding_univers...

We stopped using the solar system to measure time a while ago, and now use atomic clocks. Civil time is periodically adjusted to match the rotation of the Earth, but the amount of adjustment necessary is measured using atomic clocks, and atomic clocks are still the basis of civil time.

>Within 30 billion years of the Sun becoming a red giant

The Sun isn't expected to remain a red giant for 30 billion years, is it? More like a tenth of that, I thought.

The prospect and opportunity of rogue planets is fascinating to me.

So I'm firmly in the camp that the speed of light is a hard limit in the Universe. Any talk of wormholes, FTL and space folding just seems like wishful thinking and the product of not understanding the domain of functions (eg putting negative values into mass or energy).

Additionally there's macro evidence to this speed limit because if it wasn't a limit it would make the likelihood of encountering spacefaring civilizations that much more likely.

So given this, it seems like traveling to other stars requires some form of generational ship. And that seems like a problem because the energy required is massive and that's even before you get into issues of having reaction mass. There are workarounds for this (eg space laser propulsion) but the problems seem... significant.

So, rogue planets. I wonder if the first vessel for interstellar travel will in fact be some largish rogue body that visits the Solar System. Even something 100km wide will contain a wealth of raw materials that would otherwise be prohibitively expensive to accelerate to interstellar speeds.

And sure it might take 10,000 years or more for such a body to travel to a nearby star but there's really not a lot of difference between several centuries and 10,000 years.

What's more, such travelers could likely seed other rogue bodies they encounter along the way.

Could this be the initial vector of interstellar colonization?

As an aside, George RR Martin 40+ years ago wrote a book called Dying of the Light. I really enjoyed it just for the concept. In this book there are so-called Festival worlds. These are worlds that wander between systems. When they approach stars they get sufficiently warm and thaw out and may have oceans and atmospheres in that time. People would build cities in that time knowing it was all temporary.

> As an aside, George RR Martin 40+ years ago wrote a book called Dying of the Light. I really enjoyed it just for the concept. In this book there are so-called Festival worlds. These are worlds that wander between systems. When they approach stars they get sufficiently warm and thaw out and may have oceans and atmospheres in that time. People would build cities in that time knowing it was all temporary.

Wow so this could be the explanation for erratic seasons of unpredictable duration in ASOIAF?

There is no explanation for the erratic seasons. GRRM (just like any storyteller) creates mystery and interest in his world and fills in the details that are required, and not so many of those that are not.

This is something he is very aware of. He will tell you that like any intriguing medieval world map, his world map also has tall tales, mysteries and stories about foreign countries, big monsters and weird men, lining the edge of the map.

Everything about ASOIAF can be explained by George RR Martin's long career as a military science fiction author.

How else could one be free to build a medieval fantasy world so unburdened by historical realism?

Which long career as a military science fiction writer?

I admit aside ASOIAF I haven't read much GRRM -- his awesome Sandkings short story, and his collaboration with Lisa Tuttle, Windhaven, and I'm aware of some of his horror/fantasy fiction.

Checking on Wikipedia I don't see a lot of military scifi in the list...

Thank you, Sandkings was great!

What's the point of interstellar colonization?

It's possible that will never be interesting to us given the expense, time, and hardships involved.

We have more than enough space and resources in this solar system to support north of a trillion humans if we start building space habitats. So even if we start procreating again after our population is predicted to stabilize, we won't run out of room here very easily.

My feeling is our digital worlds will get so engrossing we will turn our attention inwards rather than outwards. I don't think that lends itself to either population growth or interstellar colonization.

If intelligent civilization is sufficiently rare, that could easily explain the Fermi paradox. They're out there, just too far away and too uninterested in expansion for us to meet.

> What's the point of interstellar colonization?

Ultimately it's to claim matter, which is the ultimate limiting factor in how long a civilization lives. For example, you talk about engrossing digital worlds. Well, those worlds require energy and energy means matter.

To be clear we're talking on truly staggering time frames here where a trillion years is a mere blink of an eye [1][2].

[1]: https://www.youtube.com/watch?v=Qam5BkXIEhQ&t=107s

[2]: https://www.youtube.com/watch?v=Pld8wTa16Jk&t=1108s

Humans may change to (or get replaced by) a form of life that doesn’t grow and/or demand resources uncontrollably and inter-competitively. It is just a relic of our natural origins: eat and breed or get eaten and outbred. When biological reproduction (or life) is over, there is no need for trillions of energy. And when we are speaking billions of years, all humane/natural conceptions become pretty naive. I bet that no one could correctly fantasize about even thousands (not to mention millions) of years from now on. Almost all of our science fiction and futurism is Ford’s “faster horses” of evolution.

Edit: I learned before that this view seems controversial to many people, but I fail to see how on these timescales “humanity” could not be just a transient spark of its own short time.

Selection pressure operates across all timescales and distance scales.

There is ample reason to believe that any prominent form of life in the galaxy would be expansionary, because otherwise it would be replaced by one that is.

There is no reason to believe that selection stops operating when we are talking about galaxy level scale.

> To be clear we're talking on truly staggering time frames here where a trillion years is a mere blink of an eye [1][2].

Well, then these hypothetical alien civilizations have barely even begun to start their blink.

I see two major dynamics that could drive interstellar colonization:

1) Eccentricity and Boredom: I think that with a solar system population in the trillions, you will inevitably have a sufficient population of eccentrics to eventually launch generational ships. This is especially likely if humanity survivea long enough for the lifetime our own sun to present a realistic limit on the survival of the species.

2) Eccentricity and Freedom: The major advantage of interstellar colonization is distance from dominant power structures in the solar sytem. I find it quite possible that there could be societies that view fleeing the solar system as their only path to survival as a cultural unit.

One of the interesting consequences of interstellar colonization in a universe without FTL travel or communication (which, by all indications, appears to be our universe) is the sheer amount of cultural diversity it would create. Even adjacent systems would have communications round-trip times on the order of single-digit years, and depending how far apart desirable systems for colonization are it could even conceivably be decades of round-trip comms lag to the nearest inhabited system. Centralization becomes impossible, and star systems would have only very weak cultural impact on their neighbors.

Not just cultural but also possibly biological/corporeal diversity as the different cultrues start to adapt to their specific local environments.

The Orions Arm collaborarive hard SF universe has very many first contacts due to this as as often two civilisations of human origin that meet each other look to each other totally alien (one can survive in liquid methane, the other near stars in hard vacuum). They did meet a few actual (and very unique) aliens but it took a lot of verification it's not just another hyper adapted modification happy ofshoot of humanity. :)

Interstellar trade of physical goods is quite impractical without FTL. If there is interstellar travel for non-colonization purposes it seems like the primary goal would be to enable low-latency communication to compensate for semantic/cultural drift that could interfere with the efficacy of the high latency communcations.

It seems to me that interstellar trade -- with or without FTL -- is quite unlikely. I wrote some thoughts on this about a year ago, (https://one.mikro2nd.net/2021/07/interstellar/) but tl;dr: If your society is capable of marshalling the resources/energy necessary for interstellar travel in the first place, you have most likely, of necessity, solved the problem of getting more resources. War seems slightly more likely because "ideology".

Ultimately I think my notion is quite similar to yours: that the primary exchanges would be culture (art, music, fashions, language, rites,...) so the things for which we want "communication".

> What's the point of interstellar colonization?

Gamma ray bursts can probably take out a whole solar system. So could rogue stars or black holes. I think humanity is neat and want it and its descendents to survive until the heat death, so interstellar colonization it is.

We have the potential for greatness. If only we could somehow tame the darker aspects of humans we would actually deserve a fate like this and probably be able to do it (or at least that's my wishful thinking).

But yeah diversification at least 100 light years around in neighboring systems would greatly increase our chances of survival any kind of random brutal event (unless one of our neighbors goes supernova). It will be more of a question of survival rather than 'do we want to colonize that other system'

We'll run out of sun at some point, even though (most) of the time left for the energetic universe is still available.

> What's the point of interstellar colonization?

The cheapest way to fully explore another stellar system is probably colonizing it, so explorers can be manufactured in situ.

You would find "the transcension hypothesis" very interesting, it's along similar lines to what you are discussing.

You or I won't go on this trip, but I'm sure some people are crazy/bold enough to do it.

And that's all it takes.

Even digital worlds need power to run and mass for hardware to run on. Eventually there will not be enough of that in Solar System and you will have to expand.

Also more source material from real world events could be useful for bootstrapping.

It seems unlikely that we would try to colonize other star systems by sending meat there— meat doesn't keep well over the necessary time scales.

It seems a better plan would be to send artificial intelligence which can remain dormant for hundreds or thousands of years. A planet could be "colonized" by building a data center on it and then running a detailed simulation of a habitable planet. In fact, that would open up far more worlds to colonization, because it substantially loosens the requirements for habitability.

Or if a simulation truly isn't good enough, then an AI could at least bootstrap a biosphere.

The most likely form of non-generational inerstellar travel is finding high efficiency methods to accelerate ships to high relatavistic speeds so that time dilation reduces the on-ship time to sub-generation scales.

This sounds appealing but there are a couple of major problems.

The first is that you have to get to a significant percentage of light speed for this to manifest itself. Even at 0.95c time is only traveling at 1/3 of normal speed [1].

Second, the energy cost for this is truly mind-boggling. Doing so when you carry the fuel seems highly impractical. The best bet are laser highways [2]. But, you need to build that first.

The upper limit of laser propulsion isn't really high enough for that level of time dilation.

Third, traveling at these speeds makes any potential impact within even a speck of dust potentially fatal.

Lastly, fun fact: such a ship actually needs to be aerodynamic. Why? Above 0.95c the drag of hydrogen atoms in the interstellar medium will start to slow you down.

[1]: https://www.fourmilab.ch/cship/timedial.html

[2]: https://www.youtube.com/watch?v=oDR4AHYRmlk

The thing will also be a weapon of mass destruction of plannet cracking potential, one "parking accident" away from making planets uninhabitable.

On the other hand a civilisation producing such things should hopefully be technically immortal with lots of distributed backups for each individual potentially affected by such accidents & resources to fix up any affected infrastructure. So still, totally worth it, go fo it! :-)

(Less advanced neighbors might still be a bit on the edge, so please be considerate.)

You could get to the nearest star in a few years and to the other side of the galaxy well within a human lifetime with "just" constant 1 g acceleration. Obviously this is far from easy but it doesn't seem like it is necessarily out of reach given a few thousand more years of continued technological development.

The quotes you put round just are doing a lot of heavy lifting. If you had a perfect photon rocket you’d only need 1000000000 kg of fuel for each kg of payload to do 1g to the centre of our galaxy and slow down again.

Okay, maybe you can use a laser or something so you don’t have to carry the fuel with you, but you’ll still need a staggering amount of energy because the rocket equation is a harsh mistress, and the relativistic version is even worse.

Yes, and there are at least 76 stars (i.e. potentially interesting destinations) within 100 light years of us [0]. So, assuming you can set an arbitrary course at 0.95c, and decelerate without turning the humans inside your ship to organic goo, you can reach quite a few interesting places.

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[0]: http://www.solstation.com/stars3/100-as.htm

Absolutely, there are huge problems and it may not ever be feasible. However, I find it far more likely that we will find a way to solve these concerns than that we will develop FTL travel.

There is an interesting book called Lockstep that explores how a civilization might work without light speed. Essentially they have perfected cryogenic sleep and the entire civilization moves in lockstep, sleeping for many years between waking up which allows for ships to move between.

The book itself is only so so but the concept is interesting non the less.

I've read a SF story like this once, woth effectively a caste of space going pilots and scientists that spend most of their time in cryosleep on board of ships going at relativistic speeds, exploring the universe and starting colonies.

As long as they don't have relations with normal humans outosde the caste they live quite normal lives, meeting their friends from the caste relativity often from subjective PoV, with potentially decades or centuries going one between such encounters.

Still if you say want to settle down and have children, you won't likely wont see anyone else from the caste ever again as the next time one of your friends ventures to the system you settled in they will only encounter your descendants, possibly a couple generations after your time.

Send a small autonomous robot; at the destination it builds a high-bandwidth radio receiver and factories; then 'upload' the colonists by radio. Much more practical if your civilization is reasonably advanced.

Hitching a ride on a fast-moving extrasolar object passing through sounds good, though it seems like finding one going the right direction (and with enough time to get aboard) would be tricky. I suppose once you landed on it you could try and alter its course with mass drivers, but of course the more massive it was, the harder that would be.

If such a rogue planet were the result of ejection from its previous planetary system, I wouldn't expect that its speed would much exceed its previous orbital velocity in terms of order of magnitude. For reference, the orbital velocity of Mercury is about 60km/s [0], which is about 130,000 mph, or 2e-4*c.

We'd certainly notice something as big as a planet coming at us when it's at around the same distance as the Oort cloud, which NASA says lies at a distance of at least 2000 AU [1], or 3e12 km. Since it would take almost 1600 years to travel 3e12 km at 60km/s, I would say we'd have a fair amount of preparation time, even if my estimate for the body's speed were off by a factor of 15. ;-)

As for choosing your course, I would say if a rogue planet is about to enter the Solar System, beggars can't be choosers.

What I find more interesting is that in order for people to live on or near such a planet, it would almost have to have enough of its own internal heat to create temperatures suitable for life. So, you're almost certainly not looking at a rocky planet with a surface. Therefore, you'd want to design your habitat to orbit or exist within the atmosphere of a gas giant. To my knowledge, there hasn't been any serious proposal for such a habitat, and I'm unaware of the sci-fi perspective on this issue.

Of course, the other issue is that at 2e-4*c, you're not going anywhere very fast. :P

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[0]: https://nssdc.gsfc.nasa.gov/planetary/factsheet/mercuryfact....

[1]: https://solarsystem.nasa.gov/solar-system/oort-cloud/overvie...

It always creeps me out when someone assumes that people will keep aging and dying in the future, including very far into the future, and would thus need "generational ships" despite all scientific advancement required to make such ships possible in the first place. Right now we're standing on the verge of ending aging. It won't be much longer until it becomes optional.

>prohibitively expensive to accelerate to interstellar speeds.

But if it's on a hyperbolic trajectory, then it would be just as hard to get to it as to escape the solar system, no?

I wonder what the theoretical distribution of speeds (relative to Earth) of random interstellar debris would be.

There was also:

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

"they maintain a breathable atmosphere by periodically retrieving pails of frozen oxygen to thaw over a fire"

I was under the (false?) impression that most physicists are on board with wormholes being a real and possible phenomenon.

It requires negative energy in current theoretical physics, which is what OP is talking about, we have no idea if that will ever actually be possible, its wishful thinking at this point.

Ok, but that isn't addressing my comment. Most people aren't qualified to evaluate the cutting edge of modern physics. I'm wondering what the experts consensus is, not anonymous internet strangers. Why should I take your word over the world's best physicists?

If they are in a pentagon formation then it is simply the Puppeteers

>"Tantalizing evidence has been uncovered for a mysterious population of

"free-floating" planets

, planets that may be alone in deep space, unbound to any host star. The results include four new discoveries that are consistent with planets of similar masses to Earth, published today in Monthly Notices of the Royal Astronomical Society.

The study, led by Iain McDonald of the University of Manchester, UK, (now based at the Open University, UK) used data obtained in 2016 during the K2 mission phase of NASA's Kepler Space Telescope. During this two-month campaign, Kepler monitored a crowded field of millions of stars near the center of our Galaxy every 30 minutes in order to find rare

gravitational microlensing events.

The study team found 27 short-duration candidate

microlensing signals that varied over timescales of between an hour and 10 days.

Many of these had been previously seen in data obtained simultaneously from the ground. However, the four shortest events are new discoveries that are consistent with planets of similar masses to Earth.

These new events do not show an accompanying longer signal that might be expected from a host star, suggesting that these new events may be free-floating planets. Such planets may perhaps have originally formed around a host star before being ejected by the gravitational tug of other, heavier planets in the system."

PDS: Absolutely, utterly fascinating!

Dare we dream that there are other free-floating planets like Earth -- somewhere else in the Universe?

Perhaps we do after this discovery!

Imagine meeting one of these planets while travelling in space, the entire planet all dark and you are ordered to investigate.

Sounds spooky, but when I try to imagine it my mind throws an exception: In any non-imaginary scenairo you wont have enough energy and reaction mass to match speed with the object. in these scenarios “ordered to investigate” means that you will do some neat observations as you and the object drifts by. And if you have somehow enough energy to match the planet’s speed then you are basically a god and you don’t really have much which can spook you.

While the story of squishy human meatsacks traveling in a tin-can braving the surface of one of these would be a compelling read it is not really realistic sadly.

You could manufacture a lot of flyby drones & get quite some data, provided you craft has enough spare mass and technological capacity.

Or possibly even have a small lander match speed (at horrendous delta-v cost) to land and explore.

https://en.wikipedia.org/wiki/Blindsight_(Watts_novel)

also https://en.wikipedia.org/wiki/Dragon%27s_Egg

Also https://www.imdb.com/title/tt0572231/ (Star Trek: Enterprise, "Rogue Planet")

https://en.wikipedia.org/wiki/Flatlander_(short_story)

If the planet isn't bound to a star and is behind the lensing object, what is illuminating the planet that it appears optically?

Wouldn't be completely dark?

The planet is the lensing object. It causes a background star to brighten slightly in a very characteristic way.

So it's entirely possible for one of these rogue planets to cross into our solar system and disrupt the stable orbits of any planet, including earth or the moon...

Sure, but a rogue planet would be far, far less disruptive than a star coming near enough to us to affect the Solar System. Such stellar flybys, according to a paper I linked in a previous comment, occur every ~23M years, and are, indeed, expected to act as a destabilizing force on the Solar System over long periods of time.

Can we use this data to calculate how many rogue planets per star are in our galaxy?

IANAA, but I believe we already had a very rough estimate, from our models of solar system formation, and it's huge - at least tens of billions and very likely much more.

Probably inadvertently click-bait title with “population” ambiguity

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