Spacecraft are propelled by two kinds of engines: liquid-fuel rockets and public enthusiasm. It's the latter--roaring since late summer when independent analyses of a Martian meteorite revealed persuasive evidence of ancient organisms--that has fueled the prospect of an adventurous spaceflight.
Seeking advantage from the excitement of the Martian rock and a geologic find in Greenland, a team of scientists has been meeting this week in San Juan Capistrano to investigate possibilities for a mission to Europa, the third moon of Jupiter. One proposal would have a probe drop a 20-pound ball onto the moon's surface, then capture part of the resulting plume of ice, dust and, perhaps, hints of life.
With temperatures on its surface seldom topping 230 degrees below zero Fahrenheit, Europa might seem an odd place to look for life. But scientists have come to believe that huge gravitational forces from Jupiter have created a warm, subsurface ocean on Europa that could be the solar system's most hospitable location for extraterrestrial life. Bolstering their theory are recent photos of Europa, taken by the Galileo spacecraft, which show fuzzy dots along dark fissures--signs of volcanoes spewing water and debris of sulfur, silicon or carbon.
Only two decades ago, it was thought that life on Earth began when the sun's energy catalyzed carbon molecules in the primordial soup. Discoveries in the late 1970s of creatures thriving in pitch-black water, however, showed that life could grow independently of light, drawing its energy from chemicals instead. Now a newly published study, based on geologic evidence from Greenland, suggests that life was thriving on Earth 300 million years earlier than previous estimates, in an era that was very hostile: Meteorites pounded the land and caused the oceans to boil.