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TRAPPIST-1’s seventh planet is a chilly world

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9:00am, May 23, 2017
TRAPPIST 1 system

FAR OUT TRAPPIST-1h (outermost magenta line) orbits its star in about 19 days, new observations show. The orbits of the system’s other six planets are shown in red, orange, yellow, green, blue and purple.

When astronomers in February announced the discovery of seven planets orbiting a supercool star, details about the outermost planet were sketchy. No more. The seventh planet is chilly and definitely no place for life, the international team reports May 22 in Nature Astronomy.

The seven-planet system, TRAPPIST-1, is 39 light-years from Earth in the constellation Aquarius. Follow-up observations of the system reveal that TRAPPIST-1h is about three-quarters the size of Earth and orbits its star in just under 19 days. The planet sits about 9.6 million kilometers from its star, which has only 8 percent of the mass of the sun. As a result, TRAPPIST-1h gets about as much starlight as the icy dwarf planet Ceres, in the asteroid belt, gets from the sun.

Such limited light makes the planet too cold (

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