New "Impossible" Planet May Be on a Death Spiral

Brian Handwerk
for National Geographic News
August 26, 2009

A newfound planet orbiting a star about 325 light-years away has astronomers believing in the impossible.

Dubbed WASP-18b, the planet is ten times more massive than Jupiter but is so close to its star that it only takes one Earth day to make a full orbit, according to a new study.

Based on current theories of how planets and their stars interact, WASP-18b simply shouldn't exist—unless it's on death's door.

It's possible astronomers have gotten a lucky glimpse of a so-called hot Jupiter about to meet its fiery end, said study co-author Coel Hellier, of the U.K.'s Keele University.

But there's also a chance the planet is a mystery that could force scientists to rethink established ideas about planetary forces known as tidal interactions.

(Related: "Planet Found Orbiting Same-Size Star.")

Gambler's Luck?

Astronomers think that massive hot Jupiters are born far away from their stars and approach them gradually during eons of orbiting.

WASP-18b is now nearly next to its star, at a distance of only 1.4 million miles (2.2 million kilometers).

Current theories say that such a massive planet so close to its star should be pulling on the host star, creating a tidal effect similar to the moon's pull on Earth.

At that range the planet's pull would be so strong that it would drain energy from its orbit, causing the planet to rapidly fall into the star.

If this is the case for WASP-18b, that world would be much closer to the end of its life than any known planet.

Continued on Next Page >>


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