The Hidden Ocean of Europa; October 1999; Scientific American Magazine; by Pappalardo, Head, Greeley; 10 Page(s)

Do living things flourish elsewhere within our solar system, or is Earth's environment uniquely nurturing? This question is central to planetary exploration today. Three decades into humankind's reconnaissance of the planets and their natural satellites, only a short list of possible abodes remains. Perhaps the most intriguing is Jupiter's ice-rich moon Europa.

For centuries, astronomers knew Europa only as a pinprick of light in even the most powerful telescopes. In the 1960s spectroscopy showed that the satellite, like many others in the cold reaches of the outer solar system, is covered with ice. With surface temperatures of 110 kelvins (-260 degrees Fahrenheit) near the equator and 50 kelvins near the poles, that ice must form a rock-hard skin. Researchers had no way to probe deeper and little reason to expect anything special. But in the past two decades and especially in the past few years, spectacular images radioed from visiting spacecraft have revealed a young and tremendously deformed surface. Somewhere under the icy shell, it seems, must be a warm, mobile interior. Is it glacial ice? Or are Europa's innards warm enough to sustain an ocean of liquid water? If the latter, we can stretch our imaginations and ask whether life might have arisen within the lightless depths.