Celestial renegades

摘要

John Johnson remembers the night he found his first blue lion. He was observing at the Subaru telescope on top of Mauna Kea in Hawaii. Earlier that evening, before he had driven up the rubble road to the volcanic summit, his collaborator Josh Winn had phoned from Massachusetts and joked, as he always did: "Tonight's the night we find a retrograde planet." A retrograde, or backwards, planet is one that orbits its parent star in the opposite sense to the star's rotation. No planet in our solar system does this, and few astronomers seriously expected to find one around another star. "It's like going on a safari and stumbling across a blue lion," says Johnson, who is at the California Institute of Technology in Pasadena.