The solar system’s spotted bully and its ringed sidekick are holding some tantalizing treasures in their gravitational clutches. Circling Jupiter and Saturn are more than a hundred moons, including some of the most promising hosts for extraterrestrial life in the solar system.

But not every one of these moons is an equal opportunity extraterrestrial petri dish. Scientists are now debating which might be best for a life-seeking mission. Their attention is focused on a frozen trio: Titan, Enceladus and Europa.

For centuries, these satellites appeared in the sky as mere points of light. Now, the three moony musketeers have personalities. Enormous Titan is exotic, the home of hydrocarbon lakes and a thick atmosphere. Tiny Enceladus spits salty water into the void around Saturn. And deceptively placid, ice-crusted Europa probably hosts a sloshing ocean so deep it tickles the moon’s rocky mantle.

Scientists don’t expect to find Europan plesiosaurs or Titanian redwoods, of course. But some experts think these moons may be the best chance for turning up tiny, animated microbes — or at least their footprints.

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