SSS 2009-08-27（在线收听）

A planet has been discovered about 325 light-years away. But what’s really interesting is that it shouldn’t exist. The planet is called WASP-18b, because it was observed by a project called WASP, the Wide Area Search for Planets. It has 10 times the mass of Jupiter, and orbits its star in less than one earth day. Because it’s crazy close to its star, only 1.4 million miles. We’re 93 million miles from the sun.

Tidal interactions should have stretched the star and slowed the planet to the point where they smashed into each other a long time ago. The research is in the August 27th issue of the journal Nature. [Scientific American is part of the Nature Publishing Group.]

WASP-18b is part of a class of planets called “hot Jupiters,” which are thought to have formed a great distance from their home stars and then migrated inward.

Researchers say this particular planet has been around for about a billion years. We may have caught it in its death throes. Or, there are unknown factors keeping the star and planet from colliding. So astrophysicists intend to keep a close eye on WASP-18b, to either catch the orbit decaying or figure out why it isn’t.

—Cynthia Graber