At least 30 separate water-ice geysers shoot from the moon Enceladus in this image. After discovering this remarkable activity in 2005, Cassini flew through the plumes and found them full of life-friendly molecules.
“Our discovery of salty liquid water bathed in heat and suffused with organic compounds under the south pole of Enceladus is, in my opinion, the most exciting discovery that has ever been made in our solar system,” Porco says. “It’s a habitable zone, and it’s accessible.”
Further observations will clarify how often the jets erupt and what produces them. A future spacecraft could collect ice from the plumes and see whether it contains biological compounds—or even living organisms. “We should go to Enceladus,” Porco says.
Pockmarked Mimas, whose enormous crater has earned it the nickname “the Death Star moon,” is, at just under 250 miles in diameter, the smallest spherical object in the solar system.