The outer planets turn out to be far livelier places than we ever expected in those distant pre-Voyager days. Io set the tone, but look at all the activity we’ve found from Enceladus to Triton, and now we’ve got continuing Cassini revelations as well as new interpretations of what the Galileo probe found around Jupiter. Some of this is striking indeed, as witness a paper called to my attention by Larry Klaes and Adam Crowl discussing what may be happening on Europa in terms of energy.

The apparent presence of that sub-ice ocean on Europa has made it of great interest for astrobiology. The problem has been the availability of energy. Christopher Chyba (Princeton University), working with Kevin Hand (Princeton) and Robert Carlson (Caltech) have used data from Galileo’s Near-Infrared Mapping Spectrometer to determine that the Jovian moon could maintain an oxidized ocean. I should have the full text of this one shortly (right now I’m working solely from the abstract), but the gist of the matter is here:

We analyzed chemical sources and sinks and concluded that the radiolytically processed surface of Europa could serve to maintain an oxidized ocean even if the surface oxidants…are delivered only once every 0.5 Gyr. If delivery periods are comparable to the observed surface age (30-70 Myr), then Europa’s ocean could reach O2 concentrations comparable to those found in terrestrial surface waters, even if ~109 moles yr-1 of hydrothermally delivered reductants consume most of the oxidant flux. Such an ocean would be energetically hospitable for terrestrial marine macrofauna. The availability of reductants could be the limiting factor for biologically useful chemical energy on Europa.

If the term ‘macrofauna’ doesn’t get your attention, nothing will. The paper is Hand, Carlson and Chyba, “Energy, Chemical Disequilibrium, and Geological Constraints on Europa,” Astrobiology Vol. 7 (6) (2007), pp. 1006-1022 (abstract). I have two other articles this team published in the same journal last summer but I’m going to hold on those until I can dig into the full text of this latest paper, hoping to place the earlier work in a broader context. So we’ll return to Europa before long for more on this encouraging study.

Meanwhile, we continue to learn more about the changeable surface of Titan, harking back to the announcement of sand dunes on that moon in 2006 and later work examining Titan’s methane lakes. Jani Radebaugh (Brigham Young University) and team, who produced these earlier finds, now look at Cassini radar images showing mountains on Titan. The researchers used light and shadow in the radar images to calculate the slope of the mountains and thus determine their height.

The study indicates that Titan’s mountains are made of water ice, the largest being a scant two kilometers from base to peak. The small scale is interesting in its own right because it suggests erosion. We have a surface whose topography, rather than being the result of impact structures, seems to offer up lively geological processes. Which is not to say that impact craters have not played their own role in some places, but that a more likely explanation for what we are seeing is crustal activity, either through compression or separation of crustal materials.

The Titan paper is Radebaugh et al., “Mountains on Titan observed by Cassini Radar,” Icarus Vol. 192, Issue 1 (December, 2007), pp. 77-91 (abstract).