We wrap up our look at the American Geophysical Union meeting last week in San Francisco with an update on Europa. An interesting point that William McKinnon (Washington University, St. Louis) made in a news briefing there has that what had been a belief that there is an ocean on Europa is now hardening into a certainty. The intriguing next step is to learn more about that ocean, and here things get tricky. Just how do you study an ocean on a distant world upon which you have yet to land?
Fortunately, magnetic variations around Europa as well as observations of how the moon flexes and deforms as it orbits Jupiter can tell us much. Thus the need for a Europa orbiter, a mission that could measure gravity and magnetic fields as well as determining surface composition. Another area of interest for such a spacecraft: Are there recent eruptions from this geologically young world? The search for hot spots from such events could get interesting, to judge from what Cassini found on Enceladus.
Complementing such work will be the use of radar sounding, which should give us a solid idea of how thick the blanket of ice over the ocean is. Donald Blankenship (University of Texas at Austin), who joined McKinnon in the briefing, noted that ice-penetrating radar should be able to locate liquid water both within and beneath the shell. “Free water within the icy shell,” Blankenship adds, “and its relationship to the underlying ocean will be a critical factor in determining the habitability of Europa.”
Image: An artist’s conception showing two possible cut-away views through Europa’s ice shell. In both heat escapes, possibly volcanically, from Europa’s rocky mantle and is carried upward by buoyant oceanic currents. If the heat from below is intense and the ice shell is thin enough (left), the ice shell can directly melt, causing what are called “chaos” on Europa, regions of what appear to be broken, rotated, and tilted ice blocks. On the other hand, if the ice shell is sufficiently thick (right), the less intense interior heat will be transferred to the warmer ice at the bottom of the shell, and additional heat is generated by tidal squeezing of the warmer ice. This warmer ice will slowly rise, flowing as glaciers do on Earth, and the slow but steady motion may also disrupt the extremely cold, brittle ice at the surface. Europa is no larger than Earth’s moon, and its internal heating stems from its eccentric orbit about Jupiter, seen in the distance. As tides raised by Jupiter in Europa’s ocean rise and fall, they may cause cracking, additional heating, and even venting of water vapor into the airless sky above Europa’s icy surface. Credit: Michael Carroll, courtesy NASA/JPL.
That issue of habitability is also more interesting given new models showing that radiation on Europa is perhaps up to two-thirds less powerful than previously thought, making the prospects for orbital spacecraft and landers a little less daunting. Moreover, reprocessing of Galileo data is telling us more about the surface of this frozen world, including the presence of carbon dioxide, which is most likely coming from the ocean below. Future orbital missions may well find compounds Galileo’s instrumentation was unable to catch.
This is an interesting point in itself. We’re collecting so much data in our recent missions that researchers can be overwhelmed with the inflow. Further analysis and reprocessing — in some cases years or decades after the fact — can tease out information that had hitherto been missed. Thus the infrastructure demand is clear: We can’t afford to lose even the most apparently insignificant datasets, a fact that would seem obvious but bears repeating given the challenge of examining old Pioneer data. In terms of both storage and format, future scientists have got to be able to recover anything a deep space probe can send.
So will we ever get some kind of vehicle able to penetrate the ice on Europa? The answer may depend on what a future Europa orbiter, when and if it is funded, finds. One project to keep an eye on as these things are debated is Stone Aerospace’s Endurance, an autonomous underwater robotic vehicle that will be deployed in Antarctica some time in 2008, testing approaches and procedures for studying a frozen ocean. The kind of biochemical maps Endurance makes may one day tell us whether anything lives on Jupiter’s most provocative moon.