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Planetary Survivor Strategy: Outeat, Outweigh, Outlast!

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Old December 31st 03, 12:36 AM
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Default Planetary Survivor Strategy: Outeat, Outweigh, Outlast!

Harvard-Smithsonian Center for Astrophysics
Press Release

Release No.: 03-26
For Immediate Release: Monday, December 29, 2003

Planetary Survivor Strategy: Outeat, Outweigh, Outlast!

Cambridge, MA - Of the first 100 stars found to harbor planets, more than
30 stars host a Jupiter-sized world in an orbit smaller than Mercury's,
whizzing around its star in a matter of days (as opposed to our solar
system where Jupiter takes 12 years to orbit the Sun). Such close orbits
result from a race between a nascent gas giant and a newborn star. In the
October 10, 2003, issue of The Astrophysical Journal Letters, astronomers
Myron Lecar and Dimitar Sasselov showed what influences this race. They
found that planet formation is a contest, where a growing planet must
fight for survival lest it be swallowed by the star that initially
nurtured it.

"The endgame is a race between the star and its giant planet," says
Sasselov. "In some systems, the planet wins and survives, but in other
systems, the planet loses the race and is eaten by the star."

Although Jupiter-sized worlds have been found orbiting incredibly close to
their parent stars, such giant planets could not have formed in their
current locations. The oven-like heat of the nearby star and dearth of raw
materials would have prevented any large planet from coalescing. "It's a
lousy neighborhood to form gas giants," says Lecar. "But we find a lot of
Jupiter-sized planets in such neighborhoods. Explaining how they got there
is a challenge."

Theorists calculate that so-called "hot Jupiters" must form farther out in
the disk of gas and dust surrounding the new star and then migrate inward.
A challenge is to halt the planet's migration before it spirals into the

A Jupiter-like world's migration is powered by the disk material outside
the planet's orbit. The outer protoplanetary disk inexorably pushes the
planet inward, even as the planet grows by accreting that outer material.
Lecar and Sasselov showed that a planet can win its race to avoid
destruction by eating the outer disk before the star eats it.

Our solar system differs from the "hot Jupiter" systems in that the race
must have ended quite early. Jupiter migrated for only a short distance
before consuming the material between it and the infant Saturn, bringing
the King of Planets to a halt. If the protoplanetary disk that birthed our
solar system had contained more matter, Jupiter might have lost the race.
Then it and the inner planets, including Earth, would have spiraled into
the Sun.

"If Jupiter goes, they all go," says Lecar.

"It's too early to say that our solar system is rare, because it's easier
to find 'hot Jupiter' systems with current detection techniques," says
Sasselov. "But we certainly can say we're fortunate that Jupiter's
migration stopped early. Otherwise, the Earth would have been destroyed,
leaving a barren solar system devoid of life."

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for
Astrophysics is a joint collaboration between the Smithsonian
Astrophysical Observatory and the Harvard College Observatory. CfA
scientists, organized into six research divisions, study the origin,
evolution and ultimate fate of the universe.

For more information, contact:

David Aguilar, Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
Phone: 617-495-7462 Fax: 617-495-7468

Christine Lafon
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
Phone: 617-495-7463, Fax: 617-495-7016


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