Data gathered from the Galileo space probe mission points not only to a large body of liquid water just below Europa's surface but also to the potential for circulating water systems underneath the icy shell encapsulating the moon and believed to be at least six miles thick. A NASA study published online on Nov. 16 in the journal Nature maintains that the body of water possibly was formed via an interaction between the surface and the moon-wide ocean believed to encompass the small world. And where there is circulation, there exists the possibility for life.
"One opinion in the scientific community has been if the ice shell is thick, that's bad for biology. That might mean the surface isn't communicating with the underlying ocean," Britney Schmidt, lead author of the study, said in a NASA statement. "Now, we see evidence that it's a thick ice shell that can mix vigorously and new evidence for giant shallow lakes. That could make Europa and its ocean more habitable."
Schmidt and her fellow researchers obtained the conclusions after the discovery of what appeared to be "chaos terrains" -- areas of dark, irregular features -- on the surface of Europa. The team studied two of these bumpy, circular formations in particular. By also studying like formations on Earth (at subglacial volcanoes and ice shelves) and creating simulation models, scientists surmised that the chaos terrains on Europa were the result of heated liquid water rising from the moon's interior and interacting with the iced surface.
The lakes are believed to melt and refreeze over a period of hundreds of thousands or even millions of years.
To lend perspective to the findings, astrobiologist Tori Hoehler, a senior research scientist at NASA's Ames Research Center in Moffett Field, Calif., notes (via Space.com) that the data suggests Europa has met not only one, but two requirements necessary to sustain life. The first is continued evidence that Europa is indeed a world of water, not just frozen on its surface but also liquid at subterranean levels. Hoehler, who did not work on the NASA study, says the second has been suggested by Schmidt and her team, the "crucial requirement" of "energy."
"What you're hearing about here today would be a way to take this surface material," Hoehler explains, "transport it potentially down into the ocean and in essence tap Europa's battery. When you tap that battery, you move from a system which checks one of the requirements for life to a system that checks a second critical requirement for life, and I think this really impacts the way we consider habitability on Europa."
Still, since there has been no direct evidential corroboration (and won't be for years to come, given NASA's current budget limitations and the budget freeze in effect for five years), NASA made the announcement weighted with caution. "The data opens up some compelling possibilities," said Mary Voytek, director of NASA's Astrobiology Program in Washington. "However, scientists worldwide will want to take a close look at this analysis and review the data before we can fully appreciate the implication of these results."
The Galileo space probe was launched from the space shuttle Atlantis in 1989. It took up orbit around Jupiter in 1995. Among the many accomplishments of the exploratory spacecraft was the first ever fly-by of an asteroid (1991), discovery of a moon orbiting an asteroid (1993), the first direct observation of a comet impacting a planet (1994), and finding evidence of subterranean ocean on Europa (1996). Galileo also found evidence of subsurface saltwater on Ganymede and Callisto. Fears that Galileo would collide with Europa and possibly contaminate its oceans led its NASA handlers to decide to end its mission and the probe was sent into the crushing gravity of Jupiter in September 2003.
Water, especially water in its liquid form, is commonly thought to be a prerequisite for life formation. If true, the latest NASA study is indicative of at least the possibility that life could exist somewhere other than Earth within the Solar System.
(photo credit: NASA / JPL / University of Arizona, Wikimedia Commons)