Mars gets the attention, but apparently a moon in the far reaches of our solar system is the spot with the greatest chance of harboring extraterrestrial beings. Via the Sydney Morning Herald:
US astronomers looking for life in the solar system believe that Europa, one of the moons of Jupiter, which has an ocean, is much more promising than desert-covered Mars, which is currently the focus of the US government’s attention.
“Europa is the most likely place in our solar system beyond Earth to possess …. life,” said Robert Pappalardo, a planetary scientist at NASA’s Jet Propulsion Laboratory (JPL). “Europa is the most promising in terms of habitability because of its relatively thin ice shelf and an ocean … And we know there are oxidants on the surface of Europa.”
The JPL and the Applied Physics Laboratory at Johns Hopkins University in Maryland developed a new exploration project named Clipper with a total coast of two billion US dollars minus the launch.

