Proxima Centauri b

[radtech497]

For Proxima b (the real one) to be resonance-locked, a'la Mercury, it would need to be influenced gravitationally by a Jovian-sized planet orbiting farther out in the Proxima system. Such a planet would likely have been detected by now, so in its absence, Proxima b is tidally locked to its star. Insofar as the planet's magnetic field is concerned, it probably has an internally-generated field perhaps 1% as strong as the one generated by Earth; however, the magnetic field generated by convection within and throughout Proxima Centauri is probably several orders of magnitude stronger and may even envelop the planet as it orbits the star. In such a case, rather than deflecting flares, there may be occasions when flares are directed to the planet by magnetic field lines. Which tends to ionize and remove whatever atmosphere may be present.

All in all, my vote is for an airless (or very nearly so) analogue of Twilight.

Radtech497

[stevebowers]

For Proxima b (the real one) to be resonance-locked, a'la Mercury, it would need to be influenced gravitationally by a Jovian-sized planet orbiting farther out in the Proxima system. Such a planet would likely have been detected by now, so in its absence, Proxima b is tidally locked to its star.

Proxima b was detected by gravitational effects and the way these affect the star's Doppler effect, and these effects would also show the gas giant eventually. You may be right; I'd quite like to know Andrew LePage's opinion on this. I'll ask him.

Insofar as the planet's magnetic field is concerned, it probably has an internally-generated field perhaps 1% as strong as the one generated by Earth; however, the magnetic field generated by convection within and throughout Proxima Centauri is probably several orders of magnitude stronger and may even envelop the planet as it orbits the star. In such a case, rather than deflecting flares, there may be occasions when flares are directed to the planet by magnetic field lines. Which tends to ionize and remove whatever atmosphere may be present.

All in all, my vote is for an airless (or very nearly so) analogue of Twilight.

Radtech497

You are probably right. A Lagrange Magshield could reduce the effects of the flares, so the planet could be protected.

[stevebowers]

Here are two simulations of Proxima b, one assuming it has 3:2 resonance,
https://www.eso.org/public/videos/eso1629h/
and one assuming it is tidally locked;
https://www.eso.org/public/videos/eso1629g/
both assume it has an icy, oceanic surface.
The tidally locked version is much more extreme, and is a typical 'eyeball world'.
The 3:2 resonance model has a long, thin slit of an ocean rather than a wide-open pupil, and is much more temperate (but still below freezing for most of its surface).

[stevebowers]

Andrew LePage has this to say

The 3:2 resonance is very possible and we see it in Mercury in our solar system because of its moderate orbital eccentricity. The chances of Proxima b settling into this rotation state depends on its orbital eccentricity (which is very poorly constrained by the current RV data) and the precise shape of the planet (which won't be known for a long time). We will get a better feel for the rotation state after we get more RV data to pin down its orbit better (hopefully about a year from now after what I'm sure will be another HARPS observation campaign this winter).

Basically it is the eccentricity that counts here, as well as the mass distribution within the planet itself. I think we'll go with 3:2 resonance (as shown in the current article) until we get more data- there aren't many 3:2 resonant planets in OA at the moment, and they have some intriguing characteristics.

[radtech497]

Proxima b experiences less than one-third the tidal force acting on Mercury, so a spin-orbit resonance may be more likely; if that is indeed the case, might a 5:2 resonance be more probable than a 3:2 resonance? I realize a 5:2 resonance would give a day of only 107.3856 hours, as opposed to one of 178.976 hours for the 3:2 case, though I suppose it might come down to the orbital eccentricity one chose to go with (an editorial decision, at least until more data comes in).

Radtech497

[Boson Collider]

I think a significant factor for habitability would be how volcanically active it is, if we consider the snowball earth episodes.

If it is in a 3:2 or 5:2 resonance and was mostly covered by oceans like Earth, an ice-albedo feedback loop that results in the planet freezing over is a serious possibility. That happened to Earth several times despite the fact that the sun is more active.

On Earth, the snowball earth episode ended due to volcanism causing CO2 buildup in the atmosphere, since a snowball Earth has no water vapor in its atmosphere and thus no rain-induced weathering process that could remove CO2 from the atmosphere.

If it is volcanically active and has the right earthlike mix of continents and oceans, maybe this planet might be stuck in a loop of repeating snowball episodes due to the lower insolation?

[stevebowers]

Curiously enough, I read Stephen Baxter's recent book Proxima this week while on holiday. Baxter describes Proxima b quite realistically, despite having written the book a couple of years before it was discovered. He describes a tidally-locked world, with some interesting quirks.

[stevebowers]

As promised, here is Proxima Centauri b in its terraformed state; I've used John Dollan's Lifthransir texture as a starting point, so it was a very quick build.

Note the purple cast of the planet- a blue Gaian atmosphere in a red dwarf system takes on a faint purple tint in Celestia, and NASA’s computer model also predicts that the exoplanet Proxima b would appear as a pale purple dot when it is imaged for the first time.