Rocky World Is 17 Times as Massive as Earth

Rocky World Is 17 Times as Massive as Earth

David A. Aguilar (CfA)

Most massive alien worlds are gas giants like Jupiter. But now, astronomers say they’ve found a new type of exoplanet: a rocky world much larger than Earth that may boast only a thin sheath of an atmosphere. The orb in question (in the foreground of artist’s concept), dubbed Kepler-10c, circles its 11-billion-year-old, sunlike star once every 45 days. Previously estimated to have a diameter about 2.3 times that of Earth (giving it a volume slightly more than 12 times our planet’s), new observations with ground-based sensors suggest that Kepler-10c is 17 times as hefty as Earth, the researchers report today in Boston at a meeting of the American Astronomical Society and in a forthcoming issue of The Astrophysical Journal. Those figures for mass and volume—which suggest a dense, rocky composition and seemingly discount a large, thick atmosphere—peg the planet as the first rocky “mega-Earth” to be found. Kepler-10c is surprising, the researchers say: Previously, astronomers surmised that any planet that massive would have gravitationally slurped up gases in its neighborhood as it formed, eventually growing to become a gas giant like those in the outer reaches of our solar system. The existence of large rocky worlds like Kepler-10c may boost the chances of potentially habitable worlds throughout the cosmos, the researchers contend.

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