TRAPPIST-1 planets could contain substantial amounts of water

TRAPPIST-1 planets could contain substantial amounts of water

Kenneth Drake
September 2, 2017

Astronomer Vincent Bourrier of the Observatoire de l'Université de Genève led an worldwide team that included scientists from NASA and MIT to attempt to determine if there's water 40 light-years away on the seven Earth-sized planets orbiting TRAPPIST-1, a system which claims the biggest number of Earth-sized planets we've found to date. "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".

Following up on the discovery, an worldwide team of scientists led by the Swiss astronomer Vincent Bourrier from the Observatoire de l'Université de Genève, used the Space Telescope Imaging Spectrograph (STIS) on the NASA/ESA Hubble Space Telescope to study the amount of ultraviolet radiation received by the individual planets of the system. Late-stage outgassing could also have contributed significant amounts of water for the outer, more massive planets after they entered the habitable zone.

"Ultraviolet radiation is an important factor in the atmospheric evolution of planets", said lead author Swiss astronomer Vincent Bourrier, from the Observatoire de l'Université de Genève. Scientists believe this water vapor is a result of intense heat caused by exposure to ultraviolet radiation. For the observation of the TRAPPIST-1, researchers took more than three months and used the Space Telescope Imaging Spectrograph (STIS) aboard Hubble Space telescope.

An global team of astronomers used the NASA/ESA Hubble Space Telescope to estimate whether there might be water on the seven earth-sized planets orbiting the nearby dwarf star TRAPPIST-1.

However, as far as finding signs of hydrogen surrounding the TRAPPIST-1 worlds, the results on that were inconclusive.

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Because hydrogen gas is so light, it can escape the atmosphere of the exoplanets and be detected by Hubble, suggesting the possible presence of atmospheric water vapour. First we were told that they were good candidates in the search for alien life, only to later find out that the ultraviolet radiation from the star probably destroyed the atmosphere and surface water of the planets before life could form. The observed amount of ultraviolet radiation emitted by TRAPPIST-1 indeed suggests that the planets could have lost very big amounts of water over the course of their history.

The level of ultraviolet energy projected onto each planet is important.

The team concluded that TRAPPIST-1b and 1c, the two innermost planets, are the most dry having lost up to 20 Earth-oceans-worth of water over the last 8 billion years.

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.