SAN FRANCISCO — Three icy volcanoes line up on Saturn’s moon Titan, giving some of the best evidence yet that explosive eruptions are possible on worlds beyond Earth.

The volcanic peaks and pits lie in a region called Sotra Facula on Titan’s southern hemisphere. The mountains rise more than 3,000 feet into the air, and the deepest hole sinks nearly 5,000 feet below the surrounding plains, geologists announced in a press conference here at the American Geophysical Union meeting Dec. 14.

“It’s a combination of features that you really can’t make any way other than volcanism,” said geophysicist Randolph Kirk of the U.S. Geological Survey. “That’s what really has excited us: We finally have some proof that Titan is an active world.”

Titan is the only body in the solar system other than Earth to have lakes, rivers, clouds, and a cycle of evaporation and mist or rainfall connecting them all. But on Titan, where temperatures hover around minus 300 degrees Fahrenheit, the flowing liquids are hydrocarbons like methane and ethane, not water.

The frigid moon is shrouded in a dense, hazy atmosphere of methane and other hydrocarbons. But astronomers think all the methane should have been broken apart by sunlight millions of years ago, suggesting that something on Titan is constantly pouring fresh methane into the atmosphere.

An icy volcano, also known as a cryovolcano, could be the methane pump scientists sought. But until now, the telltale peaks and flows indicating a volcanic eruption had been hidden.

New radar data from NASA’s Cassini spacecraft has helped astronomers build a 3-D topographical map of Sotra Facula. They saw three mountains lined up in a row. The most obvious one, which the scientists dubbed the Rose, is a single peak with a bite taken out of it and a crater 5,000 feet deep to its side. A second peak, shaped like a football stadium, lies nearby, and a third is to the north.

Measurements from Cassini’s spectrometer show evidence of some kind of magma flowing from the volcanoes to cover the surrounding planes, though what the magma is made of is still unclear. It could be a combination of water and ammonia, or it could be hydrocarbons similar to molten asphalt, candle wax or polyethylene, says planetary scientist Jeffrey Kargel of the University of Arizona, who was not involved in the new work.

“In my opinion, Sotra Facula is the best example of a cryovolcanic mountain on Titan and in the outer solar system,” Kargel said.

If the volcanic material is water-based, it could provide a comfortable place for life to take hold, Kargel suggested.

“Volcanoes on Earth are destroyers of life,” he said. “But on Titan, cryovolcanism could represent perhaps the very liquids that would form the habitat for life, and very conveniently for us, the means by which these very speculative life forms are brought to the surface and made accessible.”

Video: NASA/JPL-Caltech/USGS/University of Arizona

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