Extreme Life Forms Might be Able to Survive on Eccentric Exoplanets

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Written by Josh Rodriquez
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Jet Propulsion Laboratory, Pasadena, Calif.
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News feature: 2012-285 Sept. 11, 2012

Extreme Life Forms Might Be Able to Survive on Eccentric Exoplanets

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.php?release=2012-285&cid=release_2012-285

Astronomers have discovered a veritable rogues' gallery of odd exoplanets -- from
scorching hot worlds with molten surfaces to frigid ice balls.

And while the hunt continues for the elusive "blue dot" -- a planet with roughly the same
characteristics as Earth -- new research reveals that life might actually be able to survive
on some of the many exoplanetary oddballs that exist.

"When we're talking about a habitable planet, we're talking about a world where liquid
water can exist," said Stephen Kane, a scientist with the NASA Exoplanet Science
Institute at the California Institute of Technology in Pasadena. "A planet needs to be the
right distance from its star -- not too hot and not too cold." Determined by the size and
heat of the star, this temperature range is commonly referred to as the "habitable zone"
around a star.

Kane and fellow Exoplanet Science Institute scientist Dawn Gelino have created a
resource called the "Habitable Zone Gallery." It calculates the size and distance of the
habitable zone for each exoplanetary system that has been discovered and shows which
exoplanets orbit in this so-called "goldilocks" zone. The Habitable Zone Gallery can be
found at www.hzgallery.org . The study describing the research appears in the
Astrobiology journal and is available at http://arxiv.org/abs/1205.2429 .

But not all exoplanets have Earth-like orbits that remain at a fairly constant distance from
their stars. One of the unexpected revelations of planet hunting has been that many
planets travel in very oblong, eccentric orbits that vary greatly in distance from their
stars.

"Planets like these may spend some, but not all of their time in the habitable zone," Kane
said. "You might have a world that heats up for brief periods in between long, cold
winters, or you might have brief spikes of very hot conditions."

Though planets like these would be very different from Earth, this might not preclude
them from being able to support alien life. "Scientists have found microscopic life forms
on Earth that can survive all kinds of extreme conditions," Kane said. "Some organisms
can basically drop their metabolism to zero to survive very long-lasting, cold conditions.
We know that others can withstand very extreme heat conditions if they have a protective
layer of rock or water. There have even been studies performed on Earth-based spores,
bacteria and lichens, which show they can survive in both harsh environments on Earth
and the extreme conditions of space."

Kane and Gelino's research suggests that habitable zone around stars might be larger than
once thought, and that planets that might be hostile to human life might be the perfect
place for extremophiles, like lichens and bacteria, to survive. "Life evolved on Earth at a
very early stage in the planet's development, under conditions much harsher than they are
today," Kane said.

Kane explained that many life-harboring worlds might not be planets at all, but rather
moons of larger, gas-giant planets like Jupiter in our own solar system. "There are lots of
giant planets out there, and all of them may have moons, if they are like the giant planets
in the solar system," Kane says. "A moon of a planet that is in or spends time in a
habitable zone can be habitable itself."

As an example, Kane mentioned Titan, the largest moon of Saturn, which, despite its
thick atmosphere, is far too distant from the sun and too cold for life as we know it to
exist on its surface. "If you moved Titan closer in to the sun, it would have lots of water
vapor and very favorable conditions for life."

Kane is quick to point out that there are limits to what scientists can presently determine
about habitability on already-discovered exoplanets. "It's difficult to really know about a
planet when you don't have any knowledge about its atmosphere," he said. For example,
both Earth and Venus experience an atmospheric "greenhouse effect" -- but the runaway
effect on Venus makes it the hottest place in the solar system. "Without analogues in our
own solar system, it's difficult to know precisely what a habitable moon or eccentric
planet orbit would look like."

Still, the research suggests that habitability might exist in many forms in the galaxy -- not
just on planets that look like our own. Kane and Gelino are hard at work determining
which already-discovered exoplanets might be candidates for extremophile life or
habitable moons. "There are lots of eccentric and gas giant planet discoveries," Kane
says. "We may find some surprises out there as we start to determine exactly what we
consider habitable."

NASA's Exoplanet Science Institute at Caltech manages time allocation on the Keck
Telescope for NASA. NASA's Jet Propulsion Laboratory in Pasadena, Calif., manages
NASA's Exoplanet Exploration program office. Caltech manages JPL for NASA. More
information about exoplanets and NASA's planet-finding program is at
http://planetquest.jpl.nasa.gov .

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