Feb. 7, 2011 at 3:03 PM ET
Scientists may finally get a chance to probe Jupiter's moons Europa and Ganymede for signs of microbial life, by looking in what are thought to be liquid oceans beneath their frozen crusts.
The Europa Jupiter Systems Mission is one of three finalists vying to carry out the European Space Agency's next big mission. All three presented mission plans Feb. 3 at a conference in Paris. A final decision is expected this June.
The other two missions vying for funding are the International X-ray Observatory, which could reveal what happens in the vicinity of black holes, and Laser Interferometer Space Antenna, which will "listen" to gravitational waves, giving space-time a sort of soundtrack.
All three missions are international collaborations, so Europe's decision is tied to and will have consequences for the priorities of NASA, a partner on all three, and the Japan Aerospace Exploration Agency, a partner on IXO.
Under the joint NASA-ESA Europa Jupiter Systems Mission, NASA will target Europa, an ice-covered moon thought to harbor a liquid ocean beneath its crust; ESA will head to Ganymede, the largest moon in the solar system.
Since the two orbiters are built by different agencies, one could fly without the other, though "you get better results in tandem," noted Michele Dougherty of University College London, who made the case for the joint mission at the Paris meeting, according to Space News.
Having two spacecraft, for example, would give scientists an opportunity to study Jupiter's atmosphere and magnetosphere in three dimensions.
IXO and LISA are considered too big and complicated to fly without international collaboration. Currently, IXO's lack of technical readiness has prompted the U.S. National Academy of Sciences to rank it a lower than LISA for U.S. space-science priorities.
Boosters of both missions say technical hurdles can be cleared and will be well worth the effort. IXO promises to provide the sharpest and most sensitive X-ray views of the Universe, according to team member Kirpal Nandra.
Bernard Schutz, a director at the Albert Einstein Institute in Golm, Germany, likened LISA's ability to "hear" gravitational waves, which are ripples of space-time, would be like adding sound to a silent film of a walk through a jungle. "There are bound to be many things we didn't even expect," he told Nature News.
Which mission is set as a priority in Europe will become clearer this June. NASA has thrown preliminary support behind all three, though guidelines to be laid out March 7 in the final version of the National Academy of Sciences ranking will set the space agency's agenda.
Keep in mind, all the missions are still way out on the horizon: The one ultimately selected wouldn't launch until around 2020.
For more about these missions, check out these stories:
John Roach is a contributing writer for msnbc.com. Connect with the Cosmic Log community by hitting the "like" button on the Cosmic Log Facebook page or following msnbc.com's science editor, Alan Boyle, on Twitter (@b0yle).