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February 5, 2018
This artist’s concept shows what the TRAPPIST-1 planetary system may look like, based on available data about the planets’ diameters, masses and distances from the host star, as of February 2018.NASA/JPL-Caltech
A team of astronomers including Eric Agol of the University of Washington has found that the seven Earth-sized planets orbiting the star TRAPPIST-1 are all made mostly of rock, and some could even have more water — which can give life a chance — than Earth itself.
The research was led by Simon Grimm of the University of Bern in Switzerland, and published Feb. 5 in the journal Astronomy and Astrophysics. Agol is among about two dozen co-authors. The scientists created computer models to simulate the planets based on available information.
TRAPPIST-1 is an ultra-cool dwarf star about 40 light-years — or about 235 trillion miles — from Earth in the Aquarius constellation. Astronomers confirmed its seven potentially habitable planets in early 2017 using the NASA Spitzer Space Telescope and the European Southern Observatory’s La Silla Observatory in Chile. It is the first known system with so many Earth-sized planets orbiting a single star.
TRAPPIST-1’s seven planets — labeled TRAPPIST-1b though h, moving outward from the star — orbit more closely to it than Mercury does the sun, which would be too close for potential habitability in our own system. But because the star is faint, its habitable zone — the swath of space around it just right to allow an orbiting rocky planet to sustain water on its surface — lies closer in, so orbiting planets could still, in theory, hold liquid water. Some may be tidally locked, with the same side forever facing the star.
In fact, the worlds orbit TRAPPIST-1 so closely, a person standing on the surface of one would have a spectacular view of the neighboring planets — some appearing in …