Largest Known Planet Discovered, Astronomers Announce

Brian Handwerk
for National Geographic News
September 14, 2006

Astronomers say they have discovered what appears to be an entirely new kind of planet, an extra-large gas giant unlike any known world in our solar system or beyond.

"This questions our understanding of how giant planets are formed and evolve," said Robert Noyes, a senior physicist at the Harvard-Smithsonian Center for Astrophysics (CfA).

The planet, dubbed HAT-P-1, is located some 450 light-years from Earth in the constellation Lacerta.

It is the largest planet ever discovered and boasts a radius nearly 1.4 times larger than Jupiter's.

HAT-P-1 is also the least dense of all known planets.

"This planet is about one quarter the density of water," said Gaspar Bakos, a Hubble fellow at CfA.

"In other words, it's lighter than a giant ball of cork. Just like Saturn, it would float in a bathtub if you could find a tub big enough to hold it, but it would float almost three times higher."

Unlike more familiar gas giants, including those in our solar system, HAT-P-1 does not appear to have a solid core.

(CfA scientists also announced today a new method for detecting life on other planets.)

Planet Poses "Unsolved Problem"

The planet's large size and low density can't be explained by current theories of giant planet formation.

Scientists suggest that additional heat in its interior could account for its "puffed-up" size, but as yet they can't explain how such heat could be generated.

Continued on Next Page >>


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