Hubble Observations Suggest Water May Be Abundant on Outer TRAPPIST-1 Planets

Hubble Observations Suggest Water May Be Abundant on Outer TRAPPIST-1 Planets

Hubble Observations Suggest Water May Be Abundant on Outer TRAPPIST-1 Planets

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.

Several of the planets orbiting a nearby star may harbor "substantial amounts" of water, astronomers say, including three planets situated in a habitable part of the star's solar system.

Farther away from their parent star, the planets might have formed in an environment rich in water ice, meaning the planets could have initially had very water-rich compositions.

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.

An worldwide team of astronomers used the Hubble Space Telescope (HST) to measure the amount of ultraviolet (UV) radiation hitting all seven Trappist-1 exoplanets.

The outer planets in the system - including TRAPPIST-1e, f and g which are in the habitable zone - lost much less, equivalent to around 3 times the ocean stores on Earth.

Lower-energy UV radiation takes water molecules and splits them into hydrogen and oxygen via a process called photodissociation.

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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. "As in our own atmosphere, where ultraviolet sunlight breaks molecules apart, ultraviolet starlight can break water vapour in the atmospheres of exoplanets into hydrogen and oxygen".

The amount of ultraviolet radiation emitted by TRAPPIST-1, does indeed suggest that the planets could have lost big amounts of water - more than 20 Earth-oceans-worth of water for the inner two planets alone during the last eight billion years.

The researchers caution that these estimates are limited on account of not knowing the precise mass of each planet.

Writing in the Astronomical Journal, Bourrier said: "What we found tells us that probably the [three] inner planets are not good planets to search for life". "What our results show is that even if the outer planets were initially quite water-poor like the original Earth, they could still have some water on their surfaces".

"Our results indicate that atmospheric escape may play an important role in the evolution of these planets", said co-author Dr. Julien de Wit, of MIT. "This concludes that a few of these outer planets could have been able to hold onto some water, if they accumulated enough during their formation".

"UV radiation is an important factor in the atmospheric evolution of planets".

Using the STIS, the researchers could detect any escaped hydrogen gas around the atmosphere of each planet, which helped them determine the likelihood of atmospheric water vapor.

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