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Another TRAPPIST-1 Habitability Study

posted by Fnord666 on Wednesday January 03 2018, @03:17PM   
from the earth-2.0 dept.

takyon writes:

A study has found that the two outermost TRAPPIST-1 exoplanets are the most likely to be able to retain their atmospheres:

The last thing the planets around the red dwarf star TRAPPIST-1 need is abundant sunshine. Active eruptions and flares from the star would wreak havoc on the rocky planets in orbit. But fortunately, the outer planets might be safe from this barrage of high-energy space weather.

According to a new study in the Proceedings of the National Academy of the Sciences [DOI: 10.1073/pnas.1708010115] [DX], the outer planets of the system could cling on to their atmospheres. This finding is despite previous studies showing that TRAPPIST-1 might be so active that it blows away planetary atmospheres.

[...] The new results show that while all seven planets could retain their atmosphere, the more likely scenario is that the outermost two, -1g and -1h, have the best odds (and -1e and -1f have a weaker chance.)

This could be resolved by JWST observations.

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Original Submission

• Re:Tilt, not tidal-lockage (Score: 2) by takyon on Wednesday January 03 2018, @11:35PM

  by takyon (881) <takyonNO@SPAMsoylentnews.org> on Wednesday January 03 2018, @11:35PM (#617413) Journal

  https://en.wikipedia.org/wiki/TRAPPIST-1#Moons [wikipedia.org]

  Stephen R. Kane, writing in The Astrophysical Journal Letters, notes that TRAPPIST-1 planets are unlikely to have large moons.[55][56] The Earth's Moon has a radius 27% that of Earth, so its area (and its transit depth) is 7.4% that of Earth, which would likely have been noted in the transit study if present. Smaller moons of 200–300 km (120–190 mi) radius would likely not have been detected.

  At a theoretical level, Kane found that moons around the inner TRAPPIST-1 planets would need to be extraordinarily dense to be even theoretically possible. This is based on a comparison of the Hill sphere, which marks the outer limit of a moon's possible orbit by defining the region of space in which a planet's gravity is stronger than the tidal force of its star, and the Roche limit, which represents the smallest distance at which a moon can orbit before the planet's tides exceed its own gravity and pull it apart. These constraints do not rule out the presence of ring systems (where particles are held together by chemical rather than gravitational forces).

  If TRAPPIST-1 doesn't have many large moons, that can be blamed on the red dwarf star and the relative proximity of the known planets to the star. Even if there are undetected planets much further away from the star, they are well out of the "habitable" zone.

  Earth does have an unusually large moon in this solar system, but we still haven't gotten a single confirmed exomoon detection.

  The Kepler mission is starting to teach us what types of exoplanets seem typical (although biases exist), but we don't have any sample of large moons other than the ones in our own solar system (a sample which could be incomplete if a Planet Nine is lurking out there).

  We have observed many (presumed) rocky exoplanets more massive than Earth, which means greater Hill spheres (compared to 1 Earth mass placed at the same orbit).

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