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.
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, Europa, 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."