Jupiter’s giant moon Europa has long been a prime target for exploration, because it looks like one of the most potentially habitable place in the Solar System – its icy crust probably conceals an ocean of liquid water. So planetary scientists desperately want to find out how thick the ice is, and what sort of minerals and carbon compounds are littered around the surface.

Since the Jupiter Icy Moons Orbiter (JIMO) project bit the dust (I can’t even find a NASA weblink about it), scientists have been working on an alternative proposal to visit Europa.

Torrence Johnson, chief scientist for the Solar System Directorate at the Jet Propulsion Laboratory (JPL) in Pasadena, California, starts his outline for a Europa orbiter concept with a question: should we go there at all? His first slide shows a screengrab of grainy, pixellated text, saying, “All these worlds are yours except Europa. Attempt no landing there.”

These fateful words from 2010: Odyssey 2 shouldn’t put us off, though. Apparently Lou Friedman, executive director of the Planetary Society, once telephoned Arthur C. Clarke in Sri Lanka to check with him. “Arthur says it’s OK,” Johnson reassures the audience … [click below for more details]

The proposal itself looks quite like Cassini – same sort of mass, instruments, and gravity assists past Earth and Venus to save on fuel.

But Johnson admits that it’s a ‘flagship’ project – one that would cost billions of dollars and take much more than a decade to achieve. And in a tight budget environment, the general view of planetary scientists is that those missions ought to take a back seat in favour of smaller ‘scout’ missions, says Caltech’s Bill McKinnon. They may be less ambitious, but they’re quicker, cheaper and they keep the science flowing.

The sheer difficulty of getting to Europa, which shares its space around Jupiter with three other big moons, has always been a major stumbling block. It doesn’t help that the place is bathed in powerful radiation. And now that Cassini has found geological activity, possibly involving liquid water, on both Titan and Enceladus, these moons start to become much more attractive options for a visit than Europa – simply because they’re easier to get to and have already seen some basic reconnaissance.

That’s a point that’s been made several times already this week by Jonathan Lunine of the University of Arizona, Tucson. But there were rumblings in the astrobiology session today about the danger of switching horses mid-race. A lot of people here seem to fear that focussing their lobbying on anything other than a Europa mission will be seen as inconsistency by the suits who control the purse strings, and that could lead to nobody getting their preferred project. Then again, with a proposed 50% cut to NASA’s astrobiology budget, things seem pretty pessimistic round this corner of the conference.