by Alex Lyda
Published: Mar 06, 2006
Last modified: Mar 10, 2006
The search for life elsewhere in the solar system got a boost with
the stunning NASA announcement of geyser-like eruptions on the
surface of Enceladus, a small moon orbiting Saturn, the sixth planet
orbiting the Sun. The observations by NASA's Cassini spacecraft and
reported this month in the mass media suggest pockets of liquid
water – a key ingredient for life – near the moon's surface.
At Columbia's Astrobiology Center, known as the CAC, a cadre of
scientists is bringing this scientific inquiry closer to home by
looking into the possibility of "habitable" moons around Jupiter,
the fifth planet to orbiting the Sun.
Based in Columbia's astronomy department, the CAC brings together
experts from the Earth Institute -- specifically, the Lamont-Doherty
Earth Observatory (L-DEO), the Center for Climate Systems Research (CCSR)
and the NASA Goddard Institute for Space Studies -- and from the
health science campus, with their counterparts at the American
Museum of Natural History.
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With the help of a three-year, $300,000
NASA exobiology grant, a cross-disciplinary team made up of
scientists from these four institutions is turning its attention to
the possibility of life deep below the surface of Europa, a moon
belonging to our solar system's largest planet, Jupiter. Europa has
been a source of fascination since it was first observed by Galileo
in 1610. It became the focus of renewed scientific interest about 40
years ago, when astronomer Gerard Kuiper and others showed that its
crust was composed of water and ice.
Europa technically lies beyond the "classical habitable zone," where
life is enabled by heat from the Sun. But the theory is that for
Europa, as well as for other bodies within Earth's solar system,
life may be enabled not by solar heat but by tidal heating, whereby
entire moons undergo stretching and squeezing from the gravitational
pull of their parent planets and neighboring moons.
Jupiter has 63 moons and satellites, but the bodies that are of most
interest to scientists are the four Galilean moons: Io,
Ganymede and Callisto.
"None of these moons looks like a
tropical island," quips Caleb Scharf, the director of
astrobiology at the CAC. "But there may be some deeply hidden
pockets -- or even vast regions -- of liquid water, which have
the potential for life to occur."
Currently, there is good evidence to
suggest that a layer of liquid water could exist beneath Europa's
surface ice -- a sub-surface ocean as much as 31 miles deep. If so,
it would be the only place in the solar system besides Earth where
liquid water exists in significant quantities.
Other striking features of Europa include a series of dark streaks
crisscrossing its surface. The largest streaks are roughly 12 miles
across with diffuse outer edges and a central band of lighter
material. Apparent fields of icy "plates" pock the surface and
appear to have been broken from larger sheets and then re-frozen in
a more jumbled arrangement. They look exactly like terrestrial
sea-ice fields when viewed from above, Scharf says.
While seeking to clarify the circumstances that gave rise to moons
like Europa, the CAC scientists also are interested in the
possibilities this research opens up for finding life on moons
orbiting the so-called exoplanets.
Since most of the exoplanets discovered thus far are "gas giants"
akin to Jupiter, they may well harbor moons such as those around
Jupiter or Saturn. In fact, these moons could easily be Earth-sized,
says Scharf, adding that he and other CAC researchers have grown
excited about the possibility that Jovian moons "could serve as
prototypes for this bigger question of tidally heated 'exomoons.'"
In investigating the processes by which moons and planets form, the
CAC team will eventually be looking for ways not only to explore
Europa but also to train instruments on more distant worlds.
In the process, CAC scientists will be scrutinizing the findings of
NASA's Stardust mission and New Horizons Pluto probe for clues as to
the building blocks of nascent solar systems.
"The fun of the astrobiology
enterprise is in finding the connections between all these
disciplines, and putting together the pieces of the puzzle,"
Scharf says. "To think that tiny grains of comet material, and a
probe going to Pluto, could ultimately help us find new places
to look for life in the cosmos -- it's just too much for us
scientists to resist."