New Horizons' close approach to Jupiter on the 28th of February set up some intriguing observational possibilities. The Pluto-bound spacecraft now moves beyond the giant planet in a trajectory that takes it down Jupiter's 'magnetic tail,' where sulfur and oxygen particles from its magnetosphere eventually dissipate. Since no spacecraft has ever been in this region before, coordinating what New Horizons sees with other instruments -- both space-based and terrestrial -- can tell us much about the Jovian environment. The image below is a composite of data from the Chandra X-ray Observatory superimposed upon the latest Hubble image. Notice the x-ray activity near the poles, where Chandra is detecting aurorae. The operative mechanism seems to be interaction between the solar wind and the sulfur and oxygen ions in Jupiter's magnetic field, creating aurorae a thousand times more energetic than what we see on Earth. Image: In preparation for New Horizon's approach of Jupiter, Chandra took...

Most speculation about finding life on Europa revolves around drilling through the perhaps kilometers-deep ice to sample the ocean beneath. But paleobiologist Jere H. Lipps (University of California, Berkeley) envisions a different exercise. Lipps, who has studied polar environments for twelve years in Antarctica, notes that turnover of ice on that continent often brings organisms to the surface that would otherwise be hidden. Is ice shifting similarly on Europa? Absolutely. Looking at images of that fractured surface, we see a dynamic environment where water from beneath seems to have welled up and re-frozen. The surface is strewn with domes, ridges and tilted ice rafts. Evidence of life might be found in places where blocks of ice have pushed up to form ridges and rills. Lipps puts it this way: "This is a paleontological search strategy, which is what I do. If I want to collect fossils in Nevada, I get a map and look for likely spots, like rock outcroppings, where fossils will be...

Perhaps ten to twenty kilometers under Europa's global shell of ice there looks to be an ocean. That ice sheet is pretty thick for even our best drilling rigs but, says William B. McKinnon (Washington University, St. Louis), the deformities make a good case for its being relatively thin in comparison to the world it encircles. The smooth and largely uncratered surface implies that the ice has been active in recent geological time. McKinnon made the case for a Europa mission at the American Geophysical Union meeting last December and continues to advocate close study of the Jovian moon, which seems to offer one of the most intriguing habitats for life's development in our Solar System. The Galileo mission, due to its serious antenna problems, couldn't get enough images to see active geysering, as we've found on Saturn's moon Enceladus, but we do see what McKinnon calls "...lots of interesting ice tectonics, and surface eruptions with weird colors and spectral signatures whose...