TRAPPIST-1's Outer Planets May Harbor Water, New Study Finds


Finding seven earth-sized planets orbiting the nearby dwarf star TRAPPIST-1 was one thing, now astronomers suggest that three of the planets might still harbour substantial amounts of water, adding further weight to the idea that this trio of exoplanets could indeed be habitable. "Our results suggest that water, and potentially life, could have survived in the TRAPPIST-1 system, despite the relatively intense ultraviolet and X-ray irradiation of the planets".

The Hubble Space Telescope has spotted possible signs of water on the outer planets of TRAPPIST-1, the system with the most exoplanets in a star's habitable zone.

UV radiation plays an important in the development of a planet's atmosphere: it can break water molecules into their component hydrogen and oxygen atoms and also heats the upper atmosphere, which can then allow the hydrogen and oxygen to escape into space.

Of the seven planets in the Trappist-1 system, three are located in the habitable zone, where it's thought the conditions would be right to sustain liquid water at the surface.

These researchers used the Space Telescope Imaging Spectograph on Hubble to scrutinize how much ultraviolet radiation the TRAPPIST-1 planets receive.

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An artist's concept shows what the TRAPPIST-1 planetary system may look like, based on available data about the planets' diameters, masses and distances from the host star. The researchers probed the ultraviolet radiation received by each planet. One question on everybody's lips concerns the chances of liquid water, something scientists are now able to shed more light on thanks to fresh observations from the Hubble Space Telescope. They also looked for any hydrogen "escaping" from the atmospheres, since that detection would be an indication of water vapor. It's possible for Hubble to detect escaped hydrogen gas, which can act as a "possible indicator of atmospheric water vapor", according to the statement on the research.

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.

The team wrote in their paper that observing the TRAPPIST-1 planets over a broad wavelength range from the ultraviolet to the infrared would provide insights into the current state and the dominant physical processes shaping these planets' atmospheres.

This is especially true for the innermost two planets of the system, TRAPPIST-1b and TRAPPIST-1c, which receive the largest amount of UV energy, and could have lost more than twenty Earth-oceans-worth of water during the last eight billion years.

"Our results suggest that the outer planets are the best candidates to search for water with the upcoming James Webb Space Telescope", says Bourrier.