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Rocky planets with water and an atmosphere that could support life

NASA Artistic representation of the star TRAPPIST-1 and its seven rocky planets, some of which hold significantly more water than EarthNASA

The seven Earth-like planets orbiting TRAPPIST-1, a red dwarf star a thousand times less bright than the sun, all consist primarily of rock. Of the seven, at least five appear to have a dense atmosphere or are covered by water or ice—some of these planets could hold as much as 250 times more water than the earth’s oceans. These are the findings of a study by European and American astronomers who estimated the composition of the TRAPPIST-1 planets using data measured by ground and space telescopes. Between September 2015 and March 2017, the European Southern Observatory (ESO) and the US Space Agency (NASA) collected information about the planets during dozens of orbits around the star. TRAPPIST-1 is 40 light-years from our sun and was only confirmed to have seven planets in 2017. It was already known that the planets are similar in size to Earth, but until now scientists did not know how dense they are, which is an important factor in identifying whether they could be home to water and life. The study, coordinated by Simon Grimm from the University of Bern, Switzerland, found that the planets range from 60% to 100% of the earth’s density. Planetary composition models based on the data suggest that TRAPPIST-1c and TRAPPIST-1e have a rocky core—the latter formed of iron, like Earth. The atmosphere of TRAPPIST-1b is much thicker than that of Earth, while the masses of planets d, f, and g are 5% water—as either liquid or ice (Astronomy and Astrophysics, January 31). Another study by the same team analyzed the atmospheres of planets d, e, f, and g, concluding that the atmospheres of planets d, e, and f could be favorable to the existence of life (Nature Astronomy, February 5).