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PostPosted: Thu Mar 30, 2017 1:22 pm 
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Frequent flaring in the TRAPPIST-1 system - unsuited for life?


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PostPosted: Fri Mar 31, 2017 10:21 am 
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thrash wrote:
Assessing the Habitability of the TRAPPIST-1 System Using a 3D Climate Model

Concludes that only one of the seven ("e") may have the right conditions to maintain liquid water, but also assumes for reasons that aren't clear to me that all seven planets start out as water worlds.


Interesting. I suppose starting them as water worlds produces an optimistic upper bound for habitability of the system. After all the pessimistic lower bound case is a dead dessicated system that just stays dead, so at least this way you can see what the range of possibilities are.

Simon Hibbs

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PostPosted: Tue Apr 04, 2017 11:31 pm 
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Catastrophic evaporation of rocky planets

Perez-Becker, D. & Chiang, E. 2013 Monthly Notices of the Royal Astronomical Society 433 (3): 2294-2309.

Abstract

Short-period exoplanets can have dayside surface temperatures surpassing 2000 K, hot enough to vaporize rock and drive a thermal wind. Small enough planets evaporate completely. We construct a radiative hydrodynamic model of atmospheric escape from strongly irradiated, low-mass rocky planets, accounting for dust–gas energy exchange in the wind. Rocky planets with masses ≲ 0.1 M⊕ (less than twice the mass of Mercury) and surface temperatures ≳2000 K are found to disintegrate entirely in ≲10 Gyr. When our model is applied to Kepler planet candidate KIC 12557548b — which is believed to be a rocky body evaporating at a rate of dM/dt ≳ 0.1M Gyr−1 — our model yields a present-day planet mass of ≲ 0.02 M or less than about twice the mass of the Moon. Mass-loss rates depend so strongly on planet mass that bodies can reside on close-in orbits for Gyr with initial masses comparable to or less than that of Mercury, before entering a final short-lived phase of catastrophic mass-loss (which KIC 12557548b has entered). Because this catastrophic stage lasts only up to a few per cent of the planet's life, we estimate that for every object like KIC 12557548b, there should be 10–100 close-in quiescent progenitors with sub-day periods whose hard-surface transits may be detectable by Kepler – if the progenitors are as large as their maximal, Mercury-like sizes (alternatively, the progenitors could be smaller and more numerous). According to our calculations, KIC 12557548b may have lost ∼70 per cent of its formation mass; today we may be observing its naked iron core.

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PostPosted: Tue Apr 11, 2017 4:34 am 
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Plausible Compositions of the Seven TRAPPIST-1 Planets Using Long-term Dynamical Simulations

"...we find that most of the planets are consistent with an Earth-like composition, where TRAPPIST-1f is likely to have a volatile-rich envelope."


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PostPosted: Fri Apr 14, 2017 1:47 pm 
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Limits on the Stability of TRAPPIST-1


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PostPosted: Mon Apr 17, 2017 1:11 pm 
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Updated Masses for the TRAPPIST-1 Planets


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PostPosted: Wed Apr 19, 2017 1:59 am 
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GCM SIMULATIONS OF UNSTABLE CLIMATES IN THE HABITABLE ZONE

Kind of an odd one: tries to show that the 1-dimensional climate model developed by the second author is valid by using a 3-dimensional General Climate Model to map transition points between equilibrium states in a 0-dimensional model. The one purely useful takeaway is:

"[B]etween roughly 250 and 265 K ... no equilibriated models are found. This is because in that temperature range, sensitive albedo feedbacks with sea ice lead to either
rapid glaciation into a snowball state or a rapid thaw into a temperate state."


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PostPosted: Wed Apr 19, 2017 2:46 am 
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That is a useful takeaway.

265K is presumably the minimum global average temperature at which there equatorial warm spots warm enough for open water.

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— Brett Evill

My SFRPG setting, Flat Black

© My posts to this board are copyright under the Berne Convention. They may be quoted on the board with appropriate attribution. They may not be reproduced beyond the board except with explicit permission from me.


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PostPosted: Fri Apr 28, 2017 12:52 pm 
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Habitability of Exoplanetary Systems

PhD dissertation, by the lead author of the paper on the habitability of exomoons (above).


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PostPosted: Wed May 17, 2017 1:04 pm 
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Atmospheric escape from the TRAPPIST-1 planets and implications for habitability

"... We conclude that the outermost planets of the TRAPPIST-1 system are capable of retaining their atmospheres over billion-year timescales, and are thus likely to be habitable...."


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