A dusty red planet and an icy moon of Jupiter may hold the best hopes for scientists trying to track down extraterrestrial life, at least in this solar system.
Mars and Europa each hold the promise of liquid water and possibly life. Mars has a history that suggests water once flowed in rivers and lakes, and it may still harbor liquid water deep underground. The more distant Europa could hide a churning ocean filled with life forms beneath its icy surface, as the moon gets gravitationally squeezed by Jupiter.
Future space missions have targeted both destinations to send new robotic explorers. But the red planet represents a much closer and better known target for space explorers.
"We're much farther down the road with Mars than Europa," said Jack Farmer, an astrobiologist at the University of Arizona.
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