Des Moines Register
09-14-07
ISU astronomer aids discovery
Planet offers hope that Earth could survive sun's expansion
By PERRY BEEMAN
REGISTER STAFF WRITER
An Iowa State University astronomy professor is in on an unprecedented
scientific discovery that either bodes well for Earth's long-term survival or just
provides a scientific rarity to mull before the home planet vaporizes in a few
billion years.
Steven Kawaler and international colleagues have found a Milky Way planet, V
391 Pegasi b, that somehow survived the massive bloating some 100 million
years ago of the star it was orbiting, V 391 Pegasi in the constellation Pegasus.
Astronomers had figured planets in that position either vaporized as an
expanding star's heat engulfed them or disappeared as they tumbled into the ball
of fire. They had never found a surviving planet near a star that had gone through
the so-called red-giant phase and the huge helium flash that comes with it.
Closer to home, the sun is expected to swell until it swallows Mercury and Venus
and, in celestial terms, comes pretty close to Earth in five to six billion years.
The scientific report, released Wednesday on the Web site of the journal Nature
and Thursday in its print edition, raised the question of whether Earth could
survive the sun's journey through the same process. But 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."
Red giants develop as stars begin to deplete their core's hydrogen fuel supply.
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.
"The question has been, 'Can a planet survive that kind of heat?' Apparently, one
has," Kawaler said.
The newly discovered planet had been orbiting its star 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 now 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.
Later, when the sun shrinks, the drop in gravity is expected to send Earth
packing to an orbit somewhere just outside where Mars is now. Temperatures on
Mars can drop as low as 225 degrees below zero.
Reporter Perry Beeman can be reached at (515) 284-8538 or
pbeeman@dmreg.com