Liquid at work on Saturn’s largest moon

A joint U.S.-European mission to Saturn has delivered striking images of the planet’s largest moon, Titan. Photo, radar, and spectrometer data reveal features such as hills, lakes, and stream beds, apparently shaped by liquid processes that may involve methane and ammonia as well as water.

ESA/NASA/JPL/ University of Arizona

NASA’s Cassini craft was launched in 1997, arriving at Saturn last July. The Huygens probe, built by the European Space Agency (ESA), left Cassini in December and parachuted to the surface of Titan on 14 January.

Bigger than Mercury, Titan resembles a planet more than a moon in some ways. Its smog-like atmosphere, thick with hydrocarbons, has much in common with the atmosphere envisioned by scientists for Earth’s earliest days, more than 3.8 billion years ago. “Titan is the Peter Pan of our solar system. It’s a little world that never grew up,” said Tobias Owen (University of Hawaii) on 18 February during a news conference at the annual meeting of the American Association for the Advancement of Science.

“I think what’s clear from the data is that Titan has accreted or acquired significant amounts of ammonia, as well as water,” said Jonathan Lunine (University of Arizona). Lunine believes a liquid mixture of ammonia and water may lie below Titan’s frozen surface. Ammonia would lower the mixture’s freezing point and reduce its density to a level close to water ice. Subsurface liquid might also help explain the highly eccentric nature of Titan’s orbit. “This is a very dynamic world with a complex history that Cassini-Huygens is only beginning to elucidate,” said Lunine.

Dozens of U.S. and European institutions are contributing to the Cassini-Huygens effort, led by NASA, ESA, and Agenzia Spaziale Italiana. It has been dubbed one of the most completely integrated and collaborative space missions ever flown.

University of Arizona
University of Hawaii