Earth: A Borderline Planet for Life? (Forwarded)

Public Affairs Office
Harvard-Smithsonian Center for Astrophysics
Cambridge, Massachusetts

For more information, contact:

David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462

Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463

For Release: Wednesday, January 09, 2008 11:00:00 AM EST

Release No.: 2008-02

Earth: A Borderline Planet for Life?

Austin, TX -- Our planet is changing before our eyes, and as a result,
many species are living on the edge. Yet Earth has been on the edge of
habitability from the beginning. New work by astronomers at the
Harvard-Smithsonian Center for Astrophysics shows that if Earth had been
slightly smaller and less massive, it would not have plate tectonics --
the forces that move continents and build mountains. And without plate
tectonics, life might never have gained a foothold on our world.

"Plate tectonics are essential to life as we know it," said Diana Valencia
of Harvard University. "Our calculations show that bigger is better when
it comes to the habitability of rocky planets."

This research was the subject of a press conference at the 211th meeting
of the American Astronomical Society.

Plate tectonics involve the movement of huge chunks, or plates, of a
planet's surface. Plates spread apart from each other, slide under one
another, and even crash into each other, lifting gigantic mountain ranges
like the Himalayas. Plate tectonics are powered by magma boiling beneath
the surface, much like a bubbling pot of chocolate. The chocolate on top
cools and forms a skin or crust, just as magma cools to form the planet's
crust.

Plate tectonics are crucial to a planet's habitability because they enable
complex chemistry and recycle substances like carbon dioxide, which acts
as a thermostat and keeps Earth balmy. Carbon dioxide that was locked into
rocks is released when those rocks melt, returning to the atmosphere from
volcanoes and oceanic ridges.

"Recycling is important even on a planetary scale," Valencia explained.

Valencia and her colleagues, Richard O'Connell and Dimitar Sasselov
(Harvard University), examined the extremes to determine whether plate
tectonics would be more or less likely on different-sized rocky worlds. In
particular, they studied so-called "super-Earths" -- planets more than
twice the size of Earth and up to 10 times as massive. (Any larger, and
the planet would gather gas as it forms, becoming like Neptune or even
Jupiter.)

The team found that super-Earths would be more geologically active than
our planet, experiencing more vigorous plate tectonics due to thinner
plates under more stress. Earth itself was found to be a borderline case,
not surprisingly since the slightly smaller planet Venus is tectonically
inactive.

"It might not be a coincidence that Earth is the largest rocky planet in
our solar system, and also the only one with life," said Valencia.

Exoplanet searches have turned up five super-Earths already, although none
have life-friendly temperatures. If super-Earths are as common as
observations suggest, then it is inevitable that some will enjoy
Earth-like orbits, making them excellent havens for life.

"There are not only more potentially habitable planets, but MANY more,"
stated Sasselov, who is director of the Harvard Origins of Life
Initiative.

In fact, a super-Earth could prove to be a popular vacation destination to
our far-future descendants. Volcanic "rings of fire" could span the globe
while the equivalent of Yellowstone Park would bubble with hot springs and
burst with hundreds of geysers. Even better, an Earth-like atmosphere
would be possible, while the surface gravity would be up to three times
that of Earth on the biggest super-Earths.

"If a human were to visit a super-Earth, they might experience a bit more
back pain, but it would be worth it to visit such a great tourist spot,"
Sasselov suggested with a laugh.

He added that although a super-Earth would be twice the size of our home
planet, it would have similar geography. Rapid plate tectonics would
provide less time for mountains and ocean trenches to form before the
surface was recycled, yielding mountains no taller and trenches no deeper
than those on Earth. Even the weather might be comparable for a world in
an Earth-like orbit.

"The landscape would be familiar. A super-Earth would feel very much like
home," said Sasselov.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for
Astrophysics (CfA) 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.

[NOTE: An image supporting this release is available at
http://cfa-www.harvard.edu/press/2008/pr200802_images.html ]


.

Relevant Pages