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Largest rocky world found

At half Neptune’s size, exoplanet should be gassy — but it’s not

5:19pm, February 3, 2016
rocky planet

SOLID AS A ROCK  A planet about half the size of Neptune might be made of pure rock, making it larger than other known rocky planets (one illustrated).

When it comes to big balls of rock, exoplanet BD+20594b might have all other known worlds beat. At roughly half the diameter of Neptune, BD+20594b is 100 percent rock, researchers suggest online January 28 at The planet seems to defy recent calculations that indicate a planet this large should be gassy (SN: 8/22/15, p. 32).

BD+20594b sits about 500 light-years away in the constellation Taurus. The planet is about 16 times as massive as Earth but just a little over twice as wide, making its density about 8 grams per cubic centimeter, Néstor Espinoza, an astrophysicist at the Pontifical Catholic University of Chile in Santiago, and colleagues report. Earth’s density, by comparison, is 5.5 grams

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