http://www.cfa.harvard.edu/press/2008/pr200802.html
CfA Press Release
Release No.: 2008-02
For Release: Wednesday, January 09, 2008 11:00:00 AM EST
Earth: A Borderline Planet for Life?
[EXCERPTS]
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 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.
For more information, contact:
David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
daguilar@[EMAIL PROTECTED]
Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463
cpulliam@[EMAIL PROTECTED]
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