ESO/N. Bartmann/spaceengine.org/PA Wire
A few of the planets orbiting a star called TRAPPIST-1, which is 40 light years away, have shown another sign they might be right for life: water. A team of researchers using the Hubble Space Telescope have found hints of this key component for life at three of the seven worlds.
These three exoplanets orbit in the star’s habitable zone, the narrow corridor where temperatures are mild enough to permit liquid lakes and oceans that don’t boil away or freeze.
TRAPPIST-1 may be small and dim, but dwarf stars like it often emit powerful flares of radiation that could make water and life on its planets impossible without thick protective atmospheres.
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Vincent Bourrier at the University of Geneva in Switzerland and his colleagues tracked the UV radiation that reaches TRAPPIST-1’s planets. If there were too much UV light, no water could survive on the surface because the water molecules would break up and escape through the top of the atmosphere as hydrogen and oxygen gas.
But, for a handful of the planets around TRAPPIST-1, there’s not enough UV radiation to destroy the water molecules.
Potential for water
The system’s outer planets – including the three in the habitable zone – may have lost less than three Earth-oceans’ worth of water. The astronomers say that this means the planets could have retained “substantial” amounts of water on their surfaces.
But TRAPPIST-1 emits enough radiation for its inner planets to have lost 20 times more water in the last eight billion years than all the Earth’s oceans combined, they found.
Even though the innermost of the seven worlds are likely arid and blasted with radiation, this discovery could mean that the outer planets are more hospitable for life.
Journal reference: The Astronomical Journal, DOI: 10.3847/1538-3881/aa859c
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