Space for the day

The BBC has an article by Jonathan Amos about Enceladus, one of Saturn's moons:

The evidence for an "ocean" of water under the surface of Saturn's moon Enceladus (illustration, above) appears to be overwhelming. The little world has excited scientists ever since jets of icy material were seen squirting into space from a striped region at its south pole.
Now, exquisite measurements using NASA's Cassini probe as it flew over the moon have allowed researchers to detect the water's gravitational signal. "The measurements that we have done are consistent with the existence of a large water reservoir, about the volume of Lake Superior in North America," Professor Luciano Iess told BBC News. A European comparison would be 245 times the water mass of Lake Garda in Italy. Lake Superior has a volume of twelve thousand cubic kilometers. The amount of liquid on Enceladus would be somewhat similar. Cassini's data suggests the liquid volume lies about forty kilometers under Enceladus's ice crust. This would put it directly on top of the moon's layered, rocky interior.
The findings of Professor Iess and his team will boost the view that the five-hundred-kilometer-wide moon would be one of the best places beyond Earth to go look for the existence of microbial life.
The case for a subglacial ocean has been growing ever since Cassini first sensed a diffuse atmosphere at the moon in 2005. Subsequent observations pinned the source of this atmosphere to mineral-rich streams of water vapor flowing away from surface fractures, dubbed "tiger stripes" for their resemblance to the markings on a big cat.
Cassini even flew through the plumes to "taste" their load of salts and organic (carbon-rich) molecules.
Enceladus' orbit around Saturn is eccentric; i.e., non-circular. The giant planet's gravity should therefore be expected to squeeze and stretch the little moon as it travels this path, heating some of its ices and melting them. Some of the resulting liquid could then be hurled into space through the deep tiger fractures, although quite how this happens is not yet fully understood. Nonetheless, the new work reinforces this general picture.
It has involved measuring tiny changes in the speed of Cassini as it passed through Enceladus' own gravitational field. These changes in velocity were as small as 20 millionths of a meter per second. They enabled Professor Iess and his colleagues to map variations in the distribution of mass on the moon.
The large anomaly they spotted in the data at the southern pole is best explained by the presence of a big volume of water. "What we see is consistent with a water pocket of about eight to ten kilometers in depth, and this pocket can extend up to southern latitudes of fifty degrees around the pole," the Sapienza University of Rome researcher explained.
There is strong evidence to suspect the existence of sub-glacial oceans at a number of solar system moons. Saturn's largest satellite, Titan, probably has one. Similarly, Jupiter's moons Europa, Ganymede, and Callisto would fall into this class, and perhaps even Triton at Neptune.
Of these, Enceladus and Europa draw the most interest because it is more likely that their water would be in contact with rock. This could make for some interesting chemistry; the sort of reactions that might facilitate the emergence of life.
Professor Andrew Coates, of the UK's UCL-Mullard Space Science Laboratory, commented: "I think Enceladus has gone to the top of the charts in terms of a place where there could be life. It's got several of the things which you need for life. There's certainly the presence of heat, there's liquid water in this ocean, there's organics and that type of chemistry going on. The only question is, has there been enough time for life to develop?"
Professor David Stevenson, from the California Institute of Technology, added: "We don't have an answer to that, but there are some theoretical ideas. First, let me say that the ocean that we have found could keep things going for tens of millions of years, maybe a hundred million years, but, of course, we don't know whether the ocean is being added to at present or is freezing up. And, maybe, Enceladus does go through cycles and those cycles would be related to the eccentricity of the orbit. It's possible that the orbit has not always had the same eccentricity."

Rico says space has got more amazing stuff in it than we can even imagine: