What are Trappist-1 planets atmospheres made of?

TRAPPIST-1 planets are rocky and have complex atmospheres, new studies show

Could the TRAPPIST-1 star system host a life-friendly planet? Planetary scientists probing the bevy of small, Earth-sized worlds surrounding this not-too-distant star have found that at least a few may not look too different from our own.

 From article, (Seven Earth-sized planets circle TRAPPIST-1, an ultracool dwarf star that lies about 40 light-years away. With about 9% of our sun's mass, this star is very small and dim. That means that even though TRAPPIST-1's planets lie so close to their star that they would sit within Mercury's orbit around the sun, a number of them still could be the right temperature to hold water. And because they're so close to their star, the planets circle it frequently, making them easier to study.

For the paper in Nature Astronomy, the scientists used NASA's Hubble Space Telescope to probe the atmospheres of four of the planets in or near the star's habitable zone — the area where water could potentially exist on a planet's surface. They wanted to make sure these planets did not have puffy, hydrogen-rich atmospheres (rather like the gas giants in our own solar system). Hydrogen is a greenhouse gas, and such an atmosphere would make the planet far too hot for life. For three of those planets — d, e and f — that type of atmosphere was ruled out, which means they probably have atmospheres more like those on Venus, Earth or Mars. The jury is still out on planet g, the fourth planet that was studied.

"Basically, by ruling out this scenario, we're ruling out a scenario that would have made the planet uninhabitable," de Wit said of the planetary trio.

De Wit said the scientists are looking to study the thin atmospheric trails the TRAPPIST-1 planets' atmospheres leave behind them as they move through space, rather like the ghostly tails of comets. The hope is that any hydrogen picked up in those planetary tails could come from the breakup of molecules from a large reservoir of methane or water. Water, of course, is essential to life as we know it, while methane can be eaten and produced by living things. Alone, neither is a guarantee of finding life, but they're a promising step forward.

"So far, all the lights are green, so we'll just keep on going — and we'll see," de Wit said. "It's good to know that so far, so good.")

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