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Astronomers detect first hint of water on Trappist-1

06 September 2017

Bourrier says the exoplanets in this planetary system are ripe for further study, principally because they are relatively close and therefore brighter than many other potentially habitable exoplanets.

"An worldwide 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", reads a statement from the European Space Agency/Hubble Information Centre.

What scientists realized in the new study is that the hydrogen floating around the TRAPPIST-1 planets could indicate atmospheric water vapor. The space telescope's measurements of UV light that radiates onto these planets also tell scientists how fast the atmospheres of these planets are vanishing.

"Ultraviolet radiation is an important factor in the atmospheric evolution of planets", said Vincent Bourrier, from the Observatoire de l'Universite de Geneve in witzerland. On Earth, ultraviolet sunlight breaks molecules while in the atmosphere of exoplanets in Trappist-1 it breaks water vapor into oxygen and hydrogen. This is because the two receive the highest amount of ultraviolet radiation from the Sun.

While lower-energy ultraviolet radiation breaks up water molecules - a process called photodissociation - ultraviolet rays with more energy (XUV radiation) and X-rays heat the upper atmosphere of a planet, which allows the products of photodissociation, hydrogen and oxygen, to escape. They might be able to estimate the probability that life exists on one or more of the planets with further measurements.

As it is very light, hydrogen gas can escape the exoplanets' atmospheres and be detected around the exoplanets with Hubble, acting as a possible indicator of atmospheric water vapour.

The observed amount of ultraviolet radiation emitted by TRAPPIST-1 signifies that the planets could have lost an enormous amount of water over the course of their history. The outer planets may be home to floods of water required to support life, according to latest results from the Hubble Information Centre. The outermost planets in the habitable zone have supposedly lost only a fraction of that and are thought to be environments more ideal for sustaining liquid water.

TRAPPIST-1 is an ultra-cool dwarf star only slightly larger than Jupiter, located approximately 40 light-years (378.4 trillion km) away from Earth in the constellation Aquarius.

Water vapour is sometimes considered conclusive evidence for the presence of liquid water, however, it should be noted that water vapour could exist where liquid water does not.

"While our results suggest that the outer planets are the best candidates to search for water with the upcoming James Webb Space Telescope, they also highlight the need for theoretical studies and complementary observations at all wavelengths to determine the nature of the TRAPPIST-1 planets and their potential habitability", adds Bourrier.

Astronomers detect first hint of water on Trappist-1