Some years ago I wrote a planetarium show for the Springfield, Massachusetts facility about the search for life in the universe. The show, which Mark and I sell through Loch Ness Productions, is called Oceans in Space. In it, we talk about the formation of life on our planet, and then look around the solar system for other places where the basic needs of life (water, warmth, organic material) could be met. We implied that some of the frozen water worlds of the outer solar system, like Europa, for example, could be considered as likely places where life might get a foothold.

Another world often discussed as a possible life-bearing place is Enceladus, one of the larger Saturnian moons. It shows a number of different kinds of surface units (five terrain types, if you will), including areas that are clearly recently resurfaced from within. That means that something is heating Enceladus from within, forcing fluid to ooze out over the surface (or, possibly as ice geysers) and refreezing (which would cover up any craters or cracks that existed there).

The tortured surface of Saturn's moon Enceladus belies ongoing geological activity.The enhanced color view of Enceladus seen here is largely of the southern hemisphere and includes the south polar terrain at the bottom of the image.The south polar terrain is marked by a striking set of 'blue' fractures called "Tiger Stripes," and encircled by a conspicuous and continuous chain of folds and ridges. Planetary scientists are still making models to explain why this moon is so active.

Since heat is one of the "feeders" of life, and there's heat generated inside Enceladus (likely from tidal heating caused by gravitational squeezing), and there seems be water on (and in) Enceladus, it would make sense that life could exist on (or in) that moon, provided that life had some sort of food (chemical or biological) to feed on.

Well, as it turns out, Enceladus may not be as water-rich or hospitable to life as scientists thought. New models of this moon's interior, based on data supplied by the Cassini spacecraft in orbit in the Saturn system and discussed in this press release, suggest that maybe what we're seeing on this moon's surface may not be driven by the action of liquid water inside the moon. Instead, it might be caused by what researchers call the "dissociation of clathrate ices." Clathrates are ice compounds in which one kind of ice (say, water) is imprisoned in a matrix of another kind of ice (ammonia or methane, for example). In this case, Enceladus may well have a heat source that only needs to heat the ice a little in order to melt the ice shell. The release of some gases in the process would be enough to send plumes of material out and re-coat the surface. This may mean that there's less water on Enceladus than scientists previously estimated.

This isn't a kiss of death in the search for life in our solar system. It just means that one of the main components necessary to help life along on Enceladus isn't so abundant, making that moon less hospitable to life.

What I like about this story is that the finding IS a confirmation that the observations we're making over the long term in the outer solar system are teaching us about the mechanisms that shape those worlds, including the roles of other chemical and geological processes in icy worlds. And, just because those worlds MIGHT be able to harbor life doesn't mean they actually HAVE life—a distinction that I rarely see made in media reports about the search for extra-terrestrial life. It's one thing for a world to have the capability to sustain life (or even have the conditions where life could form). It's quite another to actually prove that life exists there. To do that, we have to see the life and we have to understand the complex chemical and geological conditions that exist there.

Labels: Cassini, Enceladus, search for life

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