A low-mass planet candidate orbiting Proxima Centauri | Hacker News Reader

A low-mass planet candidate orbiting Proxima Centauri

advances.sciencemag.org

92 pointspinewurst67 comments

1.5 AU from Proxima (so 50% farther than earth is from the sun), which is itself much less luminous than the sun? I'd imagine it's a very, very cold planet and receives many times less light than earth does.

Neat to find a planet, but it doesn't sound like one humans would want to have much to do with.

Plus at 5.8 times (+-1.9) Earth's mass it's only low mass compared to most extrasolar planets.

Still, there may be life that's happy with slow and heavy.

That massive a planet might have a thick enough atmosphere to compensate for its distance from the star?

e.g. Wasn't Mars 'warm' for quite a long time and only became really cold once it lost most of its atmosphere due to its small mass?

Titan has a darn thick atmosphere, and it's a moon of Saturn. I don't see any reason the planet from the article couldn't have an atmosphere.

Isn't some of the atmosphere being replenished from its inner geology? Also IIRC Mars lost its atmosphere due to solar winds and lack of good protective magnetic field, unlike earth with its radioactivity-fed one. I would expect Titan has it neither, but is much farther from Sun so solar winds must be a tiny fraction of intensity out there.

>IIRC Mars lost its atmosphere due to solar winds and lack of good protective magnetic field

Someone in the know correct me if I'm wrong, but I believe this is no longer the main theory, as solar wind ablation is too slow to make such a huge impact. I believe the popular explanation now is that geological reactions, i.e. gas reacting with rocks and being sequestered, played a larger part.

Solar wind as the culprit was still being tossed around in 2017.

https://www.nasa.gov/press-release/nasas-maven-reveals-most-... "The new result reveals that solar wind and radiation were responsible for most of the atmospheric loss on Mars, and the depletion was enough to transform the Martian climate."

Ah, maybe I read that geological processes were ruled out rather than being the main driver

Titan keeps its atmosphere, in part, because of Saturn's magnetosphere. It is inside it something like 95% of the time.

Radioactivity fed? Indirectly by producing heat and motion in the core?

As I understand it didn't become cold because it lost its atmosphere, it lost its atmosphere because it became cold (core solidified weakening the magnetic field). It's core solidified much sooner than Earth's will because it has much less mass so it cooled quicker.

Keep in mind that surface gravity depends very much on density. The earth is pretty dense, having a core of mostly iron. Even a rocky planet can be a lot less dense if it's iron-poor, and so could have a reasonable surface gravity (by our standards) even if several times the earth's mass.

Indeed. I learned this the hard way when I made some claim to a political science roommate about the local acceleration due to gravity near one of the outer planets and was corrected and embarrassed. It's easy to forget that gravitation is the result of many tiny things all pulling on each other, not just a few big and small things.

I looked through the paper and didn't see anything about the radius of the planet candidate. I suppose it's quite difficult to determine it from so far away. Is a value known? If so, that would obviously give a good idea about the local g.

The radius is often not known. Radius is found most easily with transiting exoplanets, which are easy to detect but also only visible if you're lined up along the plane of the exoplanet's orbit.

You can also possibly find it via imaging, but even then, since you can't directly resolve it better than a point light source, you're making assumptions about albedo that lead to a wide dispersion in possible radii. High resolution optical imaging would require a telescope roughly 1-2km in diameter. Pretty tough... and because of the glare of the star, would be nearly impossible to image with an interferometric (i.e. non-filled-aperture) telescope since the light gather power would be so low. However, astronomers are incredibly clever at pulling data out of tiny points of light, so there may be some way.

Thanks for this, it's quite interesting.

I have a friend who used to work in a lab doing super-resolution microscopy (i.e. beating the diffraction limit by various means) for use with bio/medical applications. Some of the techniques he told me about have to do with more or less taking lots of data from many images and assembling it all into something meaningful. I suppose what you're describing as "pulling data out of tiny points of light" is kind of the same thing. It's just that the scale is different.

fun fact, if you were to travel into the earths core, gravity would go up first before it started to go down as you got closer to the dense center of the earth

Most extrasolar planets that we have detected. It’s harder to detect the smaller ones, so we haven’t. Future space telescopes will have the equipment to help with this problem.

Note that this is the second planet found around Proxima Centauri. The first one is only 1.3 Earth masses and sits 0.05 AU away from the sun, which puts it in the potential habitable zone.

0.05 AU seems dangerously close to the sun?

Not for a tiny, weak star like Proxima Centauri.

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

> The host star, with about an eighth of the mass of the Sun, has a habitable zone between ∼0.0423–0.0816 AU.

I didn’t know that! Thanks :)

Hey, more mass for habitats and other stuff once we get there. :-) Planets are mass inefficient anyway. ;-)

Yeah, people keep focusing on Mars as a habitat, but it makes so much more sense to build in orbit around earth. So much closer when you need something and your internet latency would be great. But Bezos has the right idea, keep people on the planet and put the things you don't want on the planet in space rather, like industry. Even that makes little sense until you're sourcing the resources from outside earth.

Interestingly it's also a "flare star", so it occasionally gets 10 times brighter for a few minutes (over the whole spectrum, including xrays and gamma).

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

I wonder if this combined with a greenhouse atmosphere could keep it warm enough between flares. If it has life, I wonder if the flare cycle would be just as important as the seasonal cycle on earth.

Reminds me of this Vernor Vinge novel: https://en.wikipedia.org/wiki/A_Deepness_in_the_Sky

Set around a star that alternates between bright and dim, with a species that hibernates during the dim periods.

Have you read Three body problem? Park of that is about a species that likes on a planet in a (chaotic) three star system. They alternate between intense heat and freezing darkness with the occasional "golden age". The books are more earth centred but very good...

If it is tidally locked there may be a habitable zone on the planet.

On the other hand it has much more mass than Earth and so there is slim possibility it has dense atmosphere. I believe dense atmosphere to be more important that perfect temperature for habitability.

Yes, just look at Venus. Probably atmosphere composition and density matters more than distance from the sun.

Actually, what I meant is it is easier to build for cold than it is to build for vacuum. Atmosphere also contains many important elements which would be hard to get from planet's crust.

As to Venus... it is CLOSER to the Sun than Earth is, not farther.

I'm aware of the order of the planets, what I mean to say is Venus's climate has much less to do with its distance from the sun than its atmospheric composition. It'd be cooler if you moved it to Mar's orbit, but still much hotter than Earth, even although solar radiation is dropping off proportionally with r squared.

Same distance as Mars to Sun so not that far away. As long as there is a chance for it to harbour life I would say it is interesting.

The Trisolaran home world

I get excited every time I hear about a possible habitable planet, but after 10 seconds I remember that this means nothing and will mean nothing for a few centuries as we won't be able to reach any other planet that's billions of kilometers away.

Not in person, but it would be an interesting target for Breakthrough Starshot.

some novel much have been written about two civilisations multiple light years apart, communicating using messages that have latency of years...any examples ?

Vernor Vinge predicted a future galactic usenet - unreliable messages that might take a while to arrive, or need to go via multiple possible paths, are what usenet was built for.

I'm currently reading the Engines of Light trilogy by Ken MacLeod. In that universe, there is no FTL travel nor communication, but starships can travel literally at the speed of light. There are "spheres of influence" spanning some tens of lightyears, and the information delay between worlds is indeed a plot element.

Many collonial empires worked with such latency before trains, steam ships, telegraph and wireless comunication became available.

The communication delay is one of the key plot elements in The Three Body Problem books.

It's a major plot element in Forever War.

Didn't know about about this project but I read more in the past hour and it seems reachable. Too bad it already has a destination. Hope I live to see the message it comes back from this.

We can't visit, but new imaging systems like LUVOIR may give us information on what is happening there with a decent amount of detail.

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

Also the ELT (claimed to be operational starting in 2025) [1] will already allow study of the atmospheric composition of extrasolar planets (I guess that means spectroscopy).

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

LUVOIR can provide up to about 25 km imaging resolution in visible light at Jupiter

The planet is ~10,000 times further away. Back of envelope puts the resolution at 250,000km. The earth is 12,000km in diameter. At 5.8x Earth mass and assuming similar density it would be a bit more than twice as wide and 25,000km diameter is easy to work with giving the planet a width of 1/10th of a "pixel". That's not nothing. In fact it's quite a lot relative to nothing. But it's still a long way from a well resolved image.

Edit

Oops. Forgot to apply the inverse square law. 10,000x further means resolving features of 10^10 greater area.

Some sort of cryogenic hibernation for space travel is not unrealistic within the next few decades.

https://www.airspacemag.com/space/hibernation-for-space-voya...

And the Singularity is Near:

https://en.m.wikipedia.org/wiki/The_Singularity_Is_Near

Even with that I hope we get to see missions where they send unmanned craft in that direction in my lifetime. I mean it's still only Voyager and New Horizons (afaik) that have been sent on a trajectory out of our own solar system on purpose. (faux edit: looking up the wiki page, it's the 5th to escape the solar system).

An unmanned mission would probably have to go even faster, and probably has to be a bigger craft with better on-board power supply (with backups) and a big communications array. Maybe it would even need similar craft following it after a while to form a chain of communications relays on their way out.

Nitpick: 5th to reach solar escape velocity. New Horizons, Pioneer 10, and Pioneer 11 have not passed the heliopause yet, which is usually considered the "boundary" of the solar system.

>in my lifetime Well, that's easy to say for you, given your nickname. ;-)

It is extremely unrealistic within the next few decades.

Right now, there is zero requirement, or desire, to send humans into deep space.

Whats more likely to happen, is ~500 years of unmanned space exploration before we even think about sending people out there.

But the Square Kilometer Array will probably be operational in your lifetime. That instrument will be powerful enough to tell us a lot about such near objects.

> billions of kilometers

Luxury. Proxima Centauri is 40 trillion kilometers from here.

Yeah, we've already reached planets that are billions of kilometers away. Pluto is never closer than around 4.3 billion km.

We’ve reached Neptune - over 4 billion km away, and Pluto is over 5bn, so billions is a relative walk in the park.

Sadly Proxima Centauri is 40,000 billion km away, so a bit further to go.

At 500m km/year our fastest probes would take 80,000 years to get there.

Fortunately we can send emails at the speed of light!!! (of course, the alien race living on Proxima will have to be fluent in english, ASCII, TCP/IP, SMTP and a few other prerequisites in order to receive our messages in proper conditions).

Email certainly isn't delivered at the speed of light.

Congratulations! You're one of today's lucky 10,000.

http://web.mit.edu/jemorris/humor/500-miles

https://tools.ietf.org/html/rfc5321#section-4.5.3.2

anyway given that their network was 100% switched, and "time to connect to a lightly-loaded remote host on a nearby network would actually largely be governed by the speed of light distance to the destination rather than by incidental router delays."

I'm thinking it doesn't apply to email delivery to Proxima Centauri or basically most places.

on edit: though with a long enough distance to the destination it would be pretty close to speed of light as the various times to respond etc. would be negligible.

I didn't know about this and enjoyed reading it. What a pleasing little story. Thanks.

Yes it is and no it isn't.

Learn from Admiral Grace Hopper: https://www.youtube.com/watch?v=9eyFDBPk4Yw

The speed of light in fiber optic cable is about 2/3 the speed of light, which is why SpaceX's Starlink will have a potential latency advantage over oceanic fiber optics.

It also gives good perspective on what's being thrown away when you add a single ms of latency through a router or a display. 186 miles at the speed of light. Many on HN don't get this, but this is why cloud gaming is perfectly feasible if we're running with low latency displays and inputs, low distance to the edge compute, and few routing hops.

Dear beloved Friend, I know this message will come as a surprise to you, but my desire is to have business relationship with you. I'm a daughter of late Sultan of Proxima B. My father left with with 5 tons of fine gold here, on this cold planet. I'm here seeking the way to transfer funds to you and your lovely green planet into your account for investment purpose. Please answer me and provide me with your account # and routing #.

Sid Meier's Proxima Centauri

Related HN discussion I guess [1]

[1] https://news.ycombinator.com/item?id=21901268

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