This is in response to Mark Eby's post below. Mark Eby wrote:
Is the Europa mission still on indefinite hold?
Alex writes:
For the time being, yes. The previous incarnation, NASA/JPL's Europa Orbiter Project, was cancelled this past June because its pricetag had rocketed well over a billion dollars, with no end in sight. The project was renamed the X2000 Advanced Avionics Project to keep technology development alive until a new mission could be designed.
Shortly thereafter, the National Research Council's Space Studies Board completed a Solar System Exploration Survey and issued <a href="http://www.nas.edu/ssb/newfrontiersfront.html"a report entitled "New Frontiers in the Solar System - An Integrated Exploration Strategy." The report noted that a Europa orbiter mission is still a high priority among planetary scientists, though noted that its pricetag (and enabling technologies) is a recurring problem. Nevertheless, the SSES recommended a hypothetical mission, dubbed Europa Geophysical Explorer (EGE), that would fall under a new mission category called Flagship. Note that, as of this moment, EGE does not exist, but is really only a "placeholder" mission concept until NASA can decide whether to resurrect (and fund) a Europa orbiter. At any rate, quoting from the report, EGE would be:
"A Flagship mission to investigate the
probable subsurface ocean of this moon.
As one of Jupiter's moon's, enigmatic
Europa sports an overlying ice shell. The
EGE is geared to define the properties of
any interior ocean and identify the
makeup of Europa's icy face. Before
orbiting Europa, this craft also scrutinizes
Ganymede and Callisto - both believed to
have subsurface oceans. The
reconnaissance of Europa by EGE will
gain insight as to the moon's
astrobiological potential, paving the way
for future landings on the intriguing
object."
Mark Eby wrote:
Has the evidence for an ocean become so conclusive that the original goal for the Europa mission of confirming one become less important?
Is the primary goal is now scouting for a lander?
Alex writes:
It all depends on one's definition of "so conclusive," but yes, most scientists accept the presence of some sort of subsurface europan ocean. Though such an ocean has not been directly detected as yet, its presence is believed to be the most plausible explanation for the Galileo magnetometer readings. That said, confirming its presence and more importantly, mapping out its extent and configuration, would be the primary goals of any Europa orbiter mission. The real debate in the Europa community at the moment, however, is the "thin crust" vs. "thick crust" issue (see the latest, November/December 2002, issue of The Planetary Report and the article by Paul Schenk for a fairly readable summary). This is important for any future lander mission(s) and the ability to reach and explore the putative ocean.
Alex R. Blackwell
University of Hawaii