Hubble delivers hints of water on Earth-like TRAPPIST-1 system

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The seven recently discovered exoplanets orbiting the TRAPPIST-1 star 40 light-years away, are the most Earth-sized planets discovered in a single system to date. Recently, an worldwide team of scientists used the Hubble Space Telescope to assess the chances of water existing on these planets-and the results are promising.

"Ultraviolet radiation is an important factor in the atmospheric evolution of planets,"said Bourrier".

Using the NASA/ESA Hubble telescope to estimate whether there might be water on the surface of the seven planets around TRAPPIST-1, the researchers found that although the innermost planets must have lost most - if not all - of their water, the outer planets of the system might still harbour substantial amounts.

Using the Space Telescope Imaging Spectrograph (STIS) aboard Hubble, an global team of astronomers studied the amount of ultraviolet radiation being received by each of the seven TRAPPIST-1 planets, and ran calculations to determine how this radiation might be influencing the amount of water on each.

UV observations are essential to measure their high-energy irradiation, and to search for photodissociated water escaping from their putative atmospheres.

According to Bourrier, these three planets could be key targets for the upcoming James Webb Space Telescope, as well as further theoretical studies.

This artist's rendition shows what the surface of a planet in the TRAPPIST-1 system might look like.

Team member Dr Amaury Triaud, said: "Hubble's observations are of great significance, since they inform us on the irradiative environment of the Trappist-1 planets, notably on whether they can remain habitable for billions of years, like Earth has". Its presence is considered a potential indicator of atmospheric water vapor. The more potent UV rays, like XUV radiation and X-rays, heat the upper atmosphere of a planet causing hydrogen and oxygen to escape. This makes it very unlikely they would still hold enough water to support life.

Hubble can then gauge the amount of hydrogen these planets are spilling out into space, and then together with the data on the UV light hitting the atmospheres, get an idea of how much water the planets have lost over their history.

"In terms of habitability, this is a positive step forward to say that hopes are still high", said study co-author Julien de Wit, in a statement from MIT.

The models indicated the innermost planets, TRAPPIST-1b and TRAPPIST-1c, could have lost 20 times as much water as there is in Earth's oceans, since they receive the largest amount of ultraviolet energy.

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.

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