First known planet to survive red-giant phase found

By Michael Kahn

LONDON (Reuters) - Astronomers have discovered the first known planet to survive its "red-giant" phase, a period when an aging star expands and engulfs bodies orbiting it.

The discovery of the gas-giant planet three times the size of Jupiter offers a look at the future of our own solar system and what will happen to the Earth when the sun grows old and collapses, the researchers said.

Scientists found the planet some 4,500 light-years from Earth. It once orbited its star at the same distance as the Earth is now from the sun -- about eight light-minutes -- but then drifted away, the researchers said in the journal Nature.

"At present, (the) discovery is the only planetary system known to have survived its red-giant phase," Jonathan Fortney, a NASA researcher, wrote in a commentary in Nature, where the international team published its findings on Wednesday.

"This will shed light not only on our own solar system, in which Mercury, Venus and perhaps Earth will eventually be engulfed by the red-giant Sun but also the diverse array of planetary systems that are our galactic neighbors."

Scientists have identified some 250 planets orbiting stars other than our sun. Most are detected by indirect measurements such as tiny variations in the wobble of a star.

The team found this planet by chance while studying its parent star V 391 Pegasi, Don Kurtz, astrophysicist at the University of Lancashire who worked on the study, told Reuters.

Sound waves in the star cause it to pulsate and vary in brightness every few minutes. By observing these changes, astronomers can measure sound speed to see inside the star.