Enceladus’ ocean could be even better for life than we thought

The ocean of liquid water hidden beneath Enceladus’ icy crust has long made this Saturn moon one of the best prospects in the hunt for extraterrestrial life — and it’s just gotten even more promising. The discovery of heat emanating from the frozen moon’s north pole suggests that the ocean is stable on geological timescales, giving time for life to develop there.

“For the first time, we can say with certainty that Enceladus is in a stable state, which has big implications for habitability,” says Carly Howett of the University of Oxford. “We knew it had liquid water, all sorts of organic molecules, heat, but stability was really the last piece of the puzzle.”

Howett and his colleagues used data from NASA’s Cassini spacecraft, which orbited Saturn from 2004 to 2017, to look for heat escaping from Enceladus. Its interior is heated by tidal forces as it is stretched and crushed by Saturn’s gravity, but until now this heat has only been captured by the south polar regions.

For life to develop in the ocean of Enceladus, a balance would be necessary: ​​the ocean would have to emit as much heat as it emits. Measurements of heat from the South Pole don’t account for the entire heat input, but Howett and his team found that the North Pole is about 7 degrees warmer than we previously thought. Combined with the radiant heat from the south pole, this almost exactly matches the total: the ice shell is thicker around the equator, so heat only escapes in significant amounts at the poles.

This means that the ocean must be stable over long periods of time. “It’s really hard to put a number on it, but we don’t think it’s going to freeze anytime soon, or that it’s been frozen recently,” Howett says. “We know that life needs time to evolve, and now we can say that it has this stability.” In reality, discovering that life, if it exists, is a completely different story. But NASA and ESA both have missions underway to search for it over the coming decades.