Deadly Dance: Giant Planet Found Orbiting Huge Star
By Robert Roy BrittSenior Science Writer
posted: 07:00 am ET
23 January 2003
A large planet recently found orbiting a distant star serves as a preview for the likely frying fate that awaits our own planet.
The star, called HD 47536, is more than 23 times the diameter of our Sun. It is the largest star ever found to harbor a planet. The discovery was announced Wednesday.
The planet is five to 10 times heavier than Jupiter and orbits the star more than twice as far as Earth is from the Sun, or at a distance of roughly 186 million miles (300 million kilometers). It goes around the star every 712 days.
The 6th-magnitude giant star HD 47536, around which a planet has been found. CREDIT: Digital Sky Survey
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The star is in the southern constellation of Canis Major (The Great Dog) and is at the very fringe of visibility for naked-eye observers under perfectly dark skies. It is almost 400 light-years away. Only one other planet has ever been found farther from our solar system.
Along with other recent discoveries, including a planet detected in a system oftwo closely orbiting stars, astronomers are realizing that planets can grow to all sorts of sizes in a myriad of environments and orbital configurations.
The new observations were made using the European Southern Observatory's La Silla Observatory in Chile. The work was led by German astronomer Johny Setiawan.
The planet was not seen directly. Instead, it was detected by noting a gravitational wobble it induces on the star. This so-called radial-velocity method is to date the most successful used to find planets outside our solar system.
Interestingly, however, this discovery was a side show to the real work of observing giant stars in an effort to spot variations in their shape, size and output.
About two-thirds of the 80 star examined in the study were found to wobble. Some of the wobbles are probably induced by companion stars, astronomers said. But HD 47536 attracted attention and was examined more closely.
"We are very excited about this discovery because it now widens the search for exoplanets towards more massive stars," said Luca Pasquini, an ESO researcher also involved in the find.
Massive stars typically rotate very rapidly, making observations difficult. But as they age, the stars inflate and their rotation is slowed, "and we then have a much better chance of detecting possible exoplanets in orbit around them," Pasquini said.
Even though HD 47536 and its planet don't resemble the Sun and Earth, a destructive process going on there is similar to one that will occur here in a few billion years. The star is swelling so dramatically that the fraction of sky it occupies, as seen from the planet, is growing, astronomers say. Temperatures are rising, along with winds. In some tens of millions of years, the planet will literally fry.
When a similar scenarioplays out on Earth, extreme drought will prevail in the early stages, theorists say. Eventually, the oceans will evaporate. Ultimately, Earth will be incinerated. Unless, some have suggested, our world moves outward (due to the reduced gravity of a dying Sun). One team of theorists has even calculated a way to move our planet out of danger.
