March 9, 2006
(PLANETQUEST) -- Until recently, Saturn's tiny moon Enceladus was thought to be cold and dead. But stunning images obtained by NASA's Cassini mission show icy jets and towering plumes erupting from the moon's south pole, and mission scientists said Thursday they have evidence that liquid water may be the source.
The discovery has broad implications in the search for life beyond our solar system, scientists said this week. Liquid water is considered essential for life, and finding it on a body at the distance of Saturn from the sun would come as a big surprise, said Dr. Vikki Meadows, an astrobiologist at the California Institute of Technology.
Meadows is part of a science team working on the Terrestrial Planet Finder (TPF), one of several future NASA missions designed to search for Earth-like planets around other stars. TPF will have remote-sensing capabilities that could detect biological processes on distant worlds. An earlier mission, SIM PlanetQuest, will help develop a target list of potentially habitable planets.
Meadows emphasized that it's unlikely either of these missions would be able to observe moons like Enceladus around extrasolar planets. But she said the discovery will broaden current thinking about where habitable planets might be found.
"The main implication for planet-finding is that there are far more niches for life than we imagined, and that the prevalence of life may be more widespread than previously thought," she said.
 |
|
 |
 |
 |
| NASA's future planet-hunters include SIM PlanetQuest (top) and the dual Terrestrial Planet Finder observatories. |
|
Meadows said similar techniques would be used to characterize both Enceladus' environment and the environments of extrasolar terrestrial planets. "When we can't land on something, like a distant moon or planet, we rely on 'remote-sensing techniques' to determine what the surface and atmosphere are like. This can either be done on orbit or via flyby, as Cassini is doing for Enceladus, or by using powerful telescopes to observe distant planetary systems."
Enceladus isn't the only place in the solar system where liquid water may exist. Oceans appear to exist on Jupiter's moons Europa and Callisto, but they are locked under solid crusts that may be kilometers thick.
"What's really exciting about Enceladus is that this environment is accessible. We can directly observe the plume and analyze its constituents to search for the building blocks of life, and potentially send a probe or crawler into the plume vents, " Meadows said.
"Enceladus shows us that even for small, icy worlds in the outer solar system, the conditions conducive for life can occur. Now we have to determine if this kind of environment can persist long enough to life to arise. "
Dr. Wesley Traub, chief scientist in the planet-finding program at Jet Propulsion Laboratory, said the discovery is a reminder to expect the unexpected as NASA hunts for new worlds.
"The fact that here we have liquid water where you might have expected things to be frozen solid is another sign that there are conditions for life in places you don't expect." Traub said. "It broadens our horizons."
Scientists find the warm temperatures at Enceladus' south pole difficult to explain if sunlight is the only heat source. How a moon smaller in width than the state of Arizona can generate this much internal heat, and why it is concentrated at the south pole, is one of many puzzles surrounding the new discovery.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the Caltech, manages the mission for NASA's Science Mission Directorate.
Written by Randal Jackson/PlanetQuest
