Giant, ultralight planet baffles scientists:

WASHINGTON - Scientists have discovered an unusually large and light planet orbiting a star that could force them to re-examine theories about how planets are formed.

The planet, dubbed HAT-P-1, is roughly one-third larger than Jupiter but weighs only half as much, astronomers with the Harvard-Smithsonian Center for Astrophysics said Thursday.

The planet is about one-quarter the density of water, Harvard-Smithsonian fellow Gaspar Bakos in a statement. “It’s lighter than a giant ball of cork,” he said.