00:00 30 January 2009
In February, NASA and European Space Agency officials will meet in Washington, DC, to decide between two missions to the outer solar system.
Should they aim for Saturn's moon Titan, or send a pair of orbiters to explore Jupiter and some of its satellites?
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The proposed Titan mission would return to the Moon in 2029 with a NASA orbiter, as well as a balloon and lake lander contributed by the European Space Agency.
By heating air from Titan's atmosphere, the balloon, or montgolfière, would be able to drift across Titan some 10 kilometres above the surface for six months or more.
(Illustration: ESA / NASA)