Associated Press
09-15-07
Study gives hope for Earth’s survival
By THE ASSOCIATED PRESS
“The question has been, ‘Can a planet survive that kind of heat?’ Apparently, one
has.”
— Steven Kawaler, Iowa State astronomy professor
DES MOINES — Scientists have long theorized that Earth would likely vaporize
in several billion years, when the sun expands and swallows nearby planets.
Now an international report involving an Iowa State University professor is
offering hope for Earth’s long-term survival.
The study includes an unprecedented discovery of a planet that survived after
the star it orbits expanded into its so-called red giant stage.
The report, released Thursday in the journal Nature, raised the question of
whether Earth could survive the sun’s journey through the same process.
Astronomers had figured planets in that position were destroyed as an expanding
star’s heat engulfed them.
‘‘The question has been, ’Can a planet survive that kind of heat?’’’ said Steven
Kawaler, an Iowa State astronomy professor. ‘‘Apparently, one has.’’
The newly discovered Milky Way planet had been orbiting its star, V 391 Pegasi
in the constellation Pegasus, at about the same distance between Earth and the
sun. However, the planet is much larger than Earth, and its size may have helped
it survive, Kawaler said. A smaller planet might not be so fortunate.
The sun, which covers 1 percent of the Earth’s orbit, is expected to balloon to 70
to 80 percent of the Earth’s orbit as it enters the red giant phase in 5 billion to 6
billion years.
The lead scientist of the study — Roberto Silvotti of the Osservatorio
Astronomico di Capodimonte in Naples, Italy — is betting the Earth will lose the
heated battle with the sun.
‘‘As far as our planets are concerned, we expect Mercury and Venus to
disappear in the sun’s envelope, whereas Mars should survive,’’ Silvotti said.
‘‘The fate of the Earth is less clear because its position is really at the limit. It
appears more likely that the Earth will not survive the red-giant expansion of the
sun, either, but it is not for sure.’’
Kawaler coordinated an international team of observatories that tracked the star’s
behavior after initial observations led scientists to suspect a planet was nearby.
ISU’s telescope wasn’t strong enough to observe the star, but Iowa State
scientists made observations at other facilities.
Kawaler’s independent computations confirmed that a planet was the reason for
the star’s behavior — not the usual mechanics of an aging star.
Red giants develop as stars begin to deplete their core’s hydrogen fuel supply.
Even if the Earth survives the sun’s expansion, the sun will later shrink, and the
drop in gravity is expected to send Earth to an orbit somewhere just outside
where Mars is now. Temperatures on Mars can drop as low as 225 degrees
below zero.