The famous TRAPPIST-1 system, made up of seven Earth-sized planets orbiting a red dwarf 39 light-years away, is making headlines again. Because after studying the data collected by the Hubble space telescope, an international group of scientists has come to the conclusion that those worlds could host substantial amounts of water , an essential condition for life as we know it to proliferate.
In some way, this new study qualifies a more pessimistic previous report, which practically ruled out this possibility due to the high radiation received by exoplanets .
The new optimism is based on the information obtained by the Space Telescope Imaging Spectrograph (STIS), a tool that has made it possible to measure the levels of ultraviolet light that reach each of the seven rocky spheres revolving around the dwarf star TRAPPIST-1. As explained by the director of the research, the Swiss astronomer Vincent Bourrier, from the Observatory of the University of Geneva, this type of radiation is a very important factor in knowing how the atmospheres of exoplanets have evolved. “As on Earth, low-energy ultraviolet light can break water vapor molecules into their two constituent elements: oxygen and hydrogen.” It is the process known as photodissociation .
20 lost oceans
Then the more energetic UV radiation (known as extreme ultraviolet radiation or UVF) and X-rays heat the upper part of the atmospheres and allow the two products of photodissociation to escape. Therefore, the levels of ultraviolet radiation and hydrogen detected around exoplanets are a possible indicator of the water vapor present in them .
Well, according to the data from the Hubble spectrograph, the UV radiation emitted by the red dwarf would have volatilized huge amounts of water in TRAPPIST-1 worlds throughout its history, especially in the two closest to the star: TRAPPIST-1b and TRAPPIST-1c. Scientists estimate that both could have lost a volume equivalent to more than 20 Earth’s oceans during the past 8 billion years.
Here it would be impossible for life to arise, but things change in the outermost areas, including TRAPPIST-1e, TRAPPIST-1f and TRAPPIST-1g, which are located in the area considered “habitable” by scientists. These three not only would have lost much less water than their “brothers”, but also their geophysical characteristics –they are more massive– suggest that they would have been able to retain it more easily on their surface.
So the TRAPPIST-1 worlds are back at the exobiologist’s point of life, especially starting next year, when the James Webb space telescope, the heir to Hubble, is put into orbit as planned. In any case, Bourrier calls for caution: “new theoretical studies and complementary observations are needed at all wavelengths of radiation emitted by the TRAPPIST star to determine the nature of its seven planets and their true potential to host life.”
Photo: ESO / N. BARTMANN / SPACEENFINE.ORG
