CBC, Saskatchewan, Canada
09-13-07
Planet survives expansion of star to red-giant size
CBC News
In a sneak preview of the fate that could befall Earth in four billion or five billion
years, astronomers have discovered the first known planet to survive the
expansion of its local star to red-giant size.
The astronomers made the discovery while observing a star 4,500 light years
from Earth that had gone through its red-giant phase — the massive expansion
of stars such as the sun after they burn their nuclear fuel.
The discovery of a planet about three times the size of Jupiter orbiting the star
was first reported by a team of international researchers writing in the journal
Nature.
"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 neighbours," NASA
researcher Jonathan Fortney said in a commentary in Nature.
When a star like the sun burns the last of the hydrogen in its core, it expands to
the size of a so-called red giant — an expansion that can easily engulf the
existing orbits of nearby planets — before shrinking, after it expels its helium in
an explosive flash. Planets in close are either engulfed by the star or pushed into
a wider orbit.
Such a fate is expected to befall our own sun in four billion to five billion years.
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The paper's authors said the newly discovered planet once orbited the star V 391
Pegasi — which lies 4,500 light years from Earth — at about the same distance
as Earth orbits the sun.
But it drifted away to a distance about 70 per cent farther when the star — once
about the same size as our own sun — expanded its radius by more than 100
times.
However, Steve Kawaler of Iowa State University, one of the scientists
involved in the paper, cautioned that Earth might not be so lucky in its fate.
"We shouldn't take too much heart in this," he said in a statement. "This planet is
larger than Jupiter, so a smaller planet like the Earth could still be vulnerable."
As is the case with most planets discovered outside our solar system, the planet
orbiting V 391 Pegasi was not seen directly but rather inferred from indirect
measurements. It took seven years of observation to infer the existence of the
planet.