Saturn’s moon looks familiar

It has taken nine years, hundreds of millions of dollars and a huge amount of effort, but planetary scientists have finally found another place with a topography quite like Earth’s.

On July 22, they gathered around a screen at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and saw the first detailed pictures of the high latitudes of Titan, one of the moons of Saturn.

The images were eerily familiar. What the scientists saw looked like dunes, hills, valleys and – most unusual – rivers running into lakes. If further studies prove that the dark, ovoid features on the vast landscape are indeed lakes, Titan will be the only body in the solar system besides Earth possessing that geological feature.

The differences between the two places, however, are as striking as their similarities.

Titan’s surface temperature averages 292 degrees below zero Fahrenheit. The landscape, carved by wind and a constant drizzle, is made up largely of ice, not rock. It takes nearly 30 years for Saturn to orbit the sun, so each of Titan’s seasons is a little more than seven years long.

The liquid that falls from the sky and runs down into the lakes isn’t water. It is some form of liquid hydrocarbon – very possibly methane, or what we know as natural gas. In the July 27 issue of the journal Nature, scientists reported methane appears to fall on Titan in a constant, year-round drizzle.

“It is almost a parody of the Earth,” said Jonathan Lunine, a professor of planetary science at the University of Arizona. “It is very funny to go to this place and see all these processes being played out, but with very, very different materials.”

Elsewhere in the solar system – on Mars, for instance – there may once have been the cycles of weather and landscape-building that still exist on Earth. They ended billions of years ago. But they are still taking place on Titan, which is about one-third the size of Earth but nearly 10 times as far from the sun.

“This tells us that we have to go a very long way from Earth to find the processes we have here,” Lunine said.