Saturn’s largest moon, Titan, looks a lot like Earth, except in deepfreeze. It’s got a nitrogen atmosphere, along with lakes and seas, channels sculpted by rivers, and even mudflats and rain clouds. The moon is so much like our planet that it’s a frequent setting for sci-fi: the (spoiler alert) promised land for Tom Cruise’s character in Oblivion, as well as the setting for Kurt Vonnegut’s second novel.
But while Titan appears so earthlike in so many ways, it's still a very alien place. The moon’s lakes and seas are not made of H2O -- at minus 290 degrees Fahrenheit, Titan’s surface is way too cold for liquid water. Researchers believe their water is actually a mixture of hard-to-freeze hydrocarbons like methane. And Titan’s lakes are eerily smooth: where are the waves? After all, "We know there is wind on Titan," says Alex Hayes of Cornell University. "The moon's magnificent sand dunes [prove] it."
NASA's Cassini spacecraft may have found the answer. Cassini, which has been in Titan’s neighborhood since 2004, completed its 100th flyby earlier this month. Soon, and for the first time since Cassini arrived, spring will be turning to summer in Titan’s northern hemisphere (where most of the seas are), with the solstice in 2017. (Saturn takes about 29 Earth years to go around the Sun.) Scientists are really excited for this upcoming change in seasons, hoping that waves and winds on northern Titan will pick up.
Now, after years of searching for some telltale ripples, researchers say they may have detected waves in two of Titan’s lakes. If confirmed, this would be the first discovery of ocean waves beyond Earth, Nature News reports.
In 2012 and 2013, Cassini spied “specular reflections" of the Sun, or glints of sunlight off the surface of Punga Mare, one of Titan’s seas. Those reflections may come from tiny ripples no more than a couple of centimeters high disturbing the otherwise flat ocean, according to University of Idaho’s Jason Barnes, who presented at a conference on Tuesday.
Four pixels in the images taken by an onboard spectrometer are brighter than you’d expect from reflecting sunlight, Barnes explains, which means they could represent something particularly rough on the surface, like a wave or set of waves.
Another talk at the conference also hinted at waves. In 2013, Cassini spotted a mysterious island in another sea, Ligeia Mare, that appeared and then disappeared. It looked like a bright reflection in one image but couldn’t be found in any photographs taken since, according to Cornell’s Jason Hofgartner. The team concluded that the mysterious island is probably a set of waves, a group of bubbles rising from below the surface, or even a suspended mass, like an iceberg.
However, while a Cassini flyby later this summer should be able to image this particular area of Ligeia Mare again, there’s no guarantee that the probe will pass by Punga Mare in the right position again before the end of its mission in 2017.
Regardless, “Titan may be beginning to stir,” says Ralph Lorenz of the Johns Hopkins University Applied Physics Laboratory. “Oceanography is no longer just an Earth science.” Lorenz, Barnes, Hayes, and the Cassini RADAR team published a global topographic map of Titan last year.
The findings [abstracts here and here] were presented at the Lunar and Planetary Science Conference taking place in Texas this week.
Image: Titan’s hydrocarbon lakes taken by Cassini / NASA/JPL-Caltech/University of Arizona/University of Idaho