Richard A. Lovett – For National Geographic News

One of the places in the solar system most likely to have extraterrestrial life may have gotten off to a hot, highly radioactive start, scientists reported yesterday at a meeting in Houston, Texas.

Enceladus, a moon of Saturn, stunned scientists two years ago when NASA’s Cassini orbiter discovered geyser-like jets of water vapor shooting into space from its south pole. Now a new study of Enceladus’s plume finds that it’s rich in nitrogen gas. “This is interesting, because nitrogen is hard to produce in a body as small as Enceladus without significant heat,” said John Spencer, a planetary scientist with the Southwest Research Institute in Boulder, Colorado. Spencer who was not part of the study.

The find suggests that the moon’s core once reached temperatures around 1,070 degrees Fahrenheit (577 degrees Celsius)—hot enough to convert Enceladus’s internal stores of ammonia into nitrogen. This may also be hot enough to produce the possible precursors for life, said the study’s lead author, Dennis Matson of the Jet Propulsion Laboratory (JPL) in Pasadena, California.

“We’ve got an organic brew, a heat source, and liquid water—all key ingredients for life,” Matson said in a press statement. “And while no one is claiming that we have found life, by any means, we probably have evidence for a place that might be hospitable to life.”

Cassini scientist Carolyn Porco of the Space Science Institute in Boulder, Colorado, said Enceladus should be a leading candidate site for future probes in search of extraterrestrial life. “I think that if there is liquid water there, then Enceladus is the next ‘go-to’ place in the solar system.” But for now Cassini’s next step is to pass through the geyser’s plume, an encounter scheduled for March 2008. Matson discussed his research at the annual Lunar and Planetary Science Conference. His findings will appear in the April issue of the journal Icarus.

Moon Had Hot Start

Scientists agree that Enceladus’s jets indicate the moon’s interior is hot, but how hot and why remain mysterious. A theory unveiled at the conference suggests that the heat might have originated from the radioactive decay of aluminum and iron. “Enceladus is a very small body, and it’s made almost entirely of ice and rock,” said Julie Castillo of JPL in a press release. “The puzzle is how the moon developed a warm core.”

The new theory posits that heat from the decay of radioactive elements softened the moon’s interior. This allowed the pull of Saturn’s gravity to flex the moon’s hot core like a rubber ball—a process that could continue generating heat indefinitely.

Other scientists aren’t convinced that radioactive materials were the source of the moon’s internal heat. “There are quite a lot of ideas being kicked around,” said John Spencer of the Southwest Research Institute. “This is just one, [But] something had to kick-start Enceladus into [its present] state,” he added.