The Earth-Size World Next Door

摘要

THIS IS THE HEADLINE we hope for in the next few years when NASA's Kepler satellite, launchedon March 6th, has had time to work its magic. Kepler iskeenly observing more than 100,000 stars, watching forthe slight telltale dimming caused by transiting planets. Actually, the above news flash is centuries old. We'veknown of such a planet since the 18th century, when tran-sit observations allowed us to deduce that Venus — theplanet next door — is very nearly the size of Earth.