The outer planets of the TRAPPIST-1 system might be better for life than we thought. Their cores are stretched by gravity, which generates heat, and there鈥檚 a possibility these exoplanets have atmospheres, so the outermost planets could be warmer and wetter than we thought, maybe even with air.
We have very little data on the TRAPPIST-1 planets. We know their distances from their star and one another, and their approximate sizes and masses. Based on this limited information, at the Planetary Science Institute in Tucson, Arizona estimated the distribution of four materials 鈥� iron, rock, ice, and liquid water 鈥� within each planet. They also examined whether tidal forces could stretch and flex the planets鈥� cores enough to heat them from the inside.
They found that six of the seven planets have low enough densities to indicate the potential presence of water, either liquid or frozen. The one that is too dense to have any water, TRAPPIST-1c, may have erupting volcanoes on its surface like Jupiter鈥檚 moon Io, and the world closest to the star could also have a core of molten iron and rock.
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Melted in the middle
On the outermost planets, whose measured densities are uncertain enough that they could be almost entirely made of ice, tidal heating could help keep any water there liquid.
鈥淭he fact that these planets could have molten interiors could potentially allow for plate tectonics or some sort of mantle cycle like what we have on Earth, which recycles minerals and allows life to exist,鈥� says at the University of Washington in Seattle.
The star TRAPPIST-1 is relatively nearby its seven worlds, so its dangerous flares could make the planets inhospitable 鈥� especially the innermost ones. But this setup could be a boon for the outermost planets. The system鈥檚 powerful tidal effects could be excellent for prospects of life on those worlds that keep a safer distance.
鈥淚f the outer planets are ice balls, tidal heating could help maintain a subsurface ocean of some sort which could potentially host life,鈥� Luger says.
Keeping the air
If the cold outer worlds are not ice balls but instead have oceans on the surface, the staying power of those oceans depends heavily on the planets having atmospheres 鈥� without an atmosphere, there can be no surface water.
鈥淭he conclusions of this paper depend substantially on whether the planets have an atmosphere or not,鈥� says at Harvard University.
at Princeton University and his colleagues performed a simulation that showed it鈥檚 possible for all seven planets to have held onto atmospheres for at least 100 million years.
In order to聽reach this result, the researchers simulated how the stellar wind from TRAPPIST-1 would blast away ions in theoretical atmospheres of the planets. While all seven planets could potentially maintain their atmospheres, the two farthest from the star have the best chances of keeping them for the billions of years it likely takes life to develop.
And with both a tidally heated core to keep some of the water from freezing and an atmosphere to stop it evaporating, either outer planet could potentially have the warm liquid water necessary for life as we know it.
Read more: Tides on exoplanets could drive alien biological clocks
Reference:
Proceedings of the National Academy of Sciences
