Hubble Space Telescope spies possibility of liquid water in TRAPPIST-1

Muriel Hammond
September 2, 2017

An artists impression of the TRAPPIST-1 multi-planet system. The system, called TRAPPIST-1, is especially appealing because it has three planets in the habitable zone, meaning these worlds could potentially support liquid water and perhaps even life.

There could be water on multiple Earth-sized planets orbiting the recently discovered TRAPPIST-1 dwarf star - making them potentially habitable - according to an global collaboration of researchers, including the University of Warwick.

Bourrier suggested that the launch of James Webb Space Telescope, the successor to Hubble, in October 2018 could make up for the lack of conclusive data about the atmospheres of the planets.

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

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.

The solar system's inner planets, however, could have lost more than 20 Earth-oceans-worth of water during the last eight billion years.

"Earth-sized planets can capture hundreds of Earth-oceans' worth of water when they form, but it's highly dependent on so many factors, and hard to say", Wit said.

The observed amount of UV radiation emitted by the TRAPPIST-1 star indeed suggests that the planets could have lost enormous amounts of water over the course of their history. The study was led by Swiss astronomer Vincent Bourrier from the Geneva Observatory in Switzerland and colleagues.

"It is very likely that the planets formed much farther away from the star [than they are now] and migrated inwards during the first 10 million years of the system", Gillon told in an email. If the night side is icy, the day side might give way to liquid water in the area where sufficient starlight hits the surface. We caution that these estimates remain limited by the large uncertainty on the planet masses.

However, a definitive answer on the TRAPPIST-1 water question will await the arrival of better telescopes. The results suggest that the outer planets of the system might still harbour substantial amounts of water.

It shows that "atmospheric escape may play an important role in the evolution of these planets", said Julien de Wit, co-author of the study and a researcher from the Massachusetts Institute of Technology.

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. "But we need to gather more information and actually see a hint of water, which we haven't found yet". A powerful enough telescope could then see it.

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