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摘要

Earth has an evil twin, and its name is Kepler-78b. The exoplanet has roughly the same mass and density as our home world, which means it is probably a ball made mostly of rock and iron (Nature, DOI: 10.1038/ nature12767). But it orbits so near its starthat its year lasts just 8.5 Earth hours and its surface may be molten, reaching around 2700℃.