Largest Known Planet Found, Has Density of Cork

The biggest alien planet found so far is baffling scientists with properties that defy current scientific explanation.

By all rights, TrES-4, a gas giant recently discovered about 1,400 light-years away in the constellation Hercules, shouldn't exist.

The planet's size is much larger than predicted for its mass, said Georgi Mandushev of Lowell Observatory, lead author of a new study on the exoplanet.

Though 70 percent bigger than Jupiter, TrES-4 contains only three-quarters of the red giant's mass. (Related: "First Proof of Wet 'Hot Jupiter' Outside Solar System" [July 11, 2007].)

That means the alien planet is about as dense as balsa wood or cork, said Mandushev, who is part of a planet-hunting team known as the Trans-Atlantic Exoplanet Survey.

"At this point the most valuable thing about this study is it presents a challenge to our theoretical models," Mandushev said. "Most advances in science come from confrontations just like this one."