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Comment by JimboOmega | Hacker News Reader

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.

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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...

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.

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.

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

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.

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

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 :)

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

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

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

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.

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.

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.

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