Europa lake formation between surface and ocean….Credit: Britney Schmidt, U.of Texas, Austin
This story begins with chaotic terrain on a moon of Jupiter, Europa. Ever since the space probe Galileo zipped by this part of the solar system and recorded the most detailed pictures of the surface of Europa, astroscientists have pretty much come to an agreement that Europa has a lot of water underneath the icy surface; oceans of water. The question they argued about was how thick was the surface ice? Some said, “Very thick, as in tens of kilometers”; other said, “at times and at certain places, not very thick at all – three kilometers or maybe even water on the surface.” Typically, the thick-icers had believable mathematical models to back up their story. All except for the “chaotic terrain” an area on the surface of Europa that looks exactly like it has icebergs that once floated on water. The thin-icers claimed this patch. Now we can add a third point of view, call them the middle-lakers.
In a paper published in Nature [16 November 2011, paywalled, Active formation of ‘chaos terrain’ over shallow subsurface water on Europa ] a team of scientists mostly from the University of Texas, Austin have hypothesized that enormous liquid ‘lakes’ exist in the Europa ice crust, figuratively half-way between the oceans below and the rock-like surface of ice. These lakes, some with at least the volume of the Great Lakes in the United States and Canada, may provide a means of water exchange between the truly massive oceans below (more ocean water than Earth) and the surface of the moon.
The significance of this hypothesis, beside settling the thin-icer vs thick-icer controversy by saying “both” with an intermediate layer some places, is that it increases the possibility of life on Europa. This has always been considered possible – the presence of water has long been associated with life; but on a Europa with a very thick shell of ice, the chances for energy and gasses interchange with the surface might limit the development of life. The postulated existence of the lakes means there is more dynamics in the waters of Europa, which would favor life.
Of course, this is a hypothesis. That means it needs to be tested. One of these days one or more probes will be sent from Earth to Europa and now it’s at least likely one will head for the ‘chaotic terrain’ area. Not only is that the area of most interest on the surface, but probably represents the shortest distance for drilling to the waters below. For now though, scientists in the field are quite pleased to have this alternative explanation for the chaos terrain and the behavior of Europa water. It fits the available facts, which is a good start.
[SciTechStory: On the Moon or elsewhere, follow the water]