08-26-2016, 05:58 AM
(08-25-2016, 08:00 PM)radtech497 Wrote: Running a few numbers on this planet, I find the ranges of uncertainty are probably not conducive to making Proxima b a "Gaian" world, even stretching the definition to its limits. For one thing, Proxima Centauri was much more active in its youth than it is now, and even now emits X-rays at levels comparable to Sol. It has an activity period of about fourteen months (compared to about 11 years for Sol) and randomly emits flares that brighten the star by perhaps an order of magnitude. The main effect of this activity, with regard to Proxima b, is that after its primary atmosphere (mostly hydrogen and helium) had been stripped away, the intense stellar bombardment might have impeded the development of a secondary atmosphere. Beyond that, the uncertainties connected with the planet's orbital eccentricity (up to 0.35) mean that it may only transit the "habitable zone" rather than reside there, and have both a periastron and an apoastron that lay outside that zone. Third, the planet became tidally locked to its star within five millennia of its formation. Finally, the values assumed for the planet's bulk density (5515 kg/m^3, the same as Earth) and its albedo (0.30, about the same as Earth), may be entirely without merit. Even the planet's mass, ranging from a minimum of 1.27 Earth masses to a 90% probability it is not more than three Earth masses, gives quite a range,
Well, couldn't a magnetic field counteract this? Proxima b is more massive than Earth, and despite being tidally locked it still rotates once every 11 days, so I would have thought that it would develop a magnetic field. Would a magnetic field as strong as, or stronger than, Earth's blunt the effects of solar flares?
Even if solar flares are still damaging, they wouldn't affect life on the dark side of the planet (although life on the dark side would have the problem of not having a source of sunlight for photosynthesis).
Being a tidally-locked planet, Proximab would likely have a thin band of habitable land on the horizon, between the light side and the dark side.
The eccentricity problem is probably overstated: the orbital period is only 11 days! Would the planet really cool down a large amount during such a short winter? After all, the atmosphere and oceans trap heat.
We have an article on Vesperian type worlds (i.e. tidally-locked). While information about this planet is uncertain, it could well be either life-bearing or terraformable.
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I just had a look at the EG's article on Proxima Centauri. It looks like there's something wrong there: planet 2 is Lifthrasir, a cytherean-vesperian world. It has an orbital period of just over 2 earth days, which is much shorter than the real planet Proximab's orbital period of 11 earth days - however, Lifthrasir's semimajor axis of 0.09 AU is apparently longer than Proximab's semi-major axis of 0.05 AU?
There must be some problem there; the orbital data on that article probably needs rechecking.