Stability of Super-Earth atmospheres in M dwarf habitable zones

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Stability of Super-Earth atmospheres in M dwarf habitable zones

Post by Sirius_Alpha on 11th March 2012, 8:35 pm

On the Stability of Super Earth Atmospheres
http://arxiv.org/abs/1203.1922

We investigate the stability of super Earth atmospheres around M stars using a 7-parameter, analytical framework. We construct stability diagrams in the parameter space of exoplanetary radius versus semi-major axis and elucidate the regions in which stable atmospheres may exist. We find that super Earth atmospheres with higher mean molecular weights and enhanced metallicities occupy a smaller region of allowed parameter space, because of the dual effects of diminished advection and enhanced radiative cooling. Furthermore, many super Earths which reside within the habitable zones of M stars may not possess stable, Earth-like atmospheres. We apply our stability diagrams to GJ 436b and GJ 1214b, and demonstrate that Earth-like elemental compositions for their atmospheres are disfavoured if these exoplanets possess solid surfaces and shallow atmospheres. Finally, we construct stability diagrams tailored to the Kepler dataset, for G and K stars, and predict that about half of the exoplanetary candidates are expected to habour stable atmospheres if Earth-like conditions are assumed. We include 55 Cancri e and CoRoT-7b in our stability diagram for G stars.

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Re: Stability of Super-Earth atmospheres in M dwarf habitable zones

Post by Lazarus on 12th March 2012, 2:13 pm

Hmmmm interesting. So maybe M dwarfs are not such a good place to look for habitable worlds after all. Of course, this needs to be tested with observations.
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Re: Stability of Super-Earth atmospheres in M dwarf habitable zones

Post by ciceron on 24th March 2012, 3:03 pm

Well , not for earth based life as we know it , anyway.

M stars have so long time spans in the main sequence that any possible path to life we could conceive has had at least one chance to arise and prosper.

I think that the main problem with habitability in the M dwarfs vincinity are they tendency to flare. Of course , maybe life in those systems need the flares as trigger for their life-cycles. As always , we are limited for the one sample we know of habitability conditions.

I've skimmed over the paper , and seems to be very sound , albeit there are factors i don't see there , like the ratio of fisionable material , thickness of the crust and mantle , etc , to better isolate the factors that could lead to the outgassing being an important factor or a minor player. A big magnetosphere , proportional to the one on Earth might made a huge diference on the results.

As far as i can see , they had only considered the core as a conduction mechanism for heat transfer on tidally locked planets, wich is a safe bet on the planets around the hz of a M star on the long run, but not a sure thing. Molten cores and liquid mantles could make the tidal lock a little slippery to reach.

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