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From bad to worse: Hard-luck planet gradually being devoured by its host star

The views expressed are those of the author and are not necessarily those of Scientific American.


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WASP 12bNew observations from the Hubble Space Telescope appear to confirm a dour prognosis for a scorching hot extrasolar planet—the distant world is being consumed by its host star.

The giant planet WASP 12 b, discovered in 2008, orbits its star at the uncomfortably close distance of only about 3.4 million kilometers. For comparison, the Earth–sun distance is about 150 million kilometers. To make matters worse, the star, known as WASP 12, is somewhat larger and hotter than our own sun, leaving its neighboring planet a searing 2,250 degrees Celsius. WASP 12 b and its host star, which lie 870 light-years away from Earth, are named for the search that spotted the planet, the SuperWASP (Wide Angle Search for Planets) project, which has telescopes on the Canary Islands in Spain and in South Africa.

In the May 10 issue of the Astrophysical Journal Letters, an international research group presents spectroscopic observations of WASP 12 b, which indicate that the planet is surrounded by a gas cloud extending roughly 60,000 kilometers from its surface. The extended exosphere is so large, and the planet so close to its star, that WASP 12 b is likely losing mass rapidly to its star.

The exospheric measurements provide some observational backup for an earlier theoretical model of the planet’s dissipation. In a study published in Nature in February, another group modeled WASP 12 b’s mass loss, finding that it gives away roughly one ten-millionth of its total mass each year. (Scientific American is part of Nature Publishing Group.) Given WASP 12 b’s heft, some 1.4 times the mass of Jupiter, that would mean that the scorching world loses as much mass in just seven years as is contained in all of Earth’s oceans.

Whether that means that WASP 12 b will be completely devoured in 10 million years remains unclear. Carole Haswell, an astrophysicist at the Open University in England and a co-author of the new study, says she expects the rate of mass loss will change with time. But with so many lingering uncertainties about the planet and its orbital evolution, she says, one cannot say for sure. It could prove to be a moot point, in any case—the authors of the February Nature paper noted that the planet may be spiraling in toward its host star on about the same time frame.

Artist’s conception of the star WASP 12 pulling material away from its planet WASP 12 b: NASA, ESA, and G. Bacon (STScI)

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  1. 1. Wayne Williamson 5:37 pm 05/24/2010

    cool article…just wondering how they can determine if the lost mass is being sucked in to the star or being blown way in to space…(the pic shows it being pulled to the star)

    Also reminds me of a recent article that shows planets moving around until they finally stabilize in to an orbit…what if this one is not stable and continues to fall in to the star…might not last the 10 million years mentioned…

    Link to this

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