Bouncing off of Titan's Lakes
On June 18th, NASA’s Cassini spacecraft successfully completed a flyby of Titan. In the process, the craft performed some tricky maneuvers and collected new data about the moon’s surface and atmosphere. Cassini passed just 3,659 kilometers above the surface and bounced a radio signal off of Titan toward Earth. The signal was then received by ground stations in NASA’s Deep Space Network. It was a complicated stunt, but the Cassini mission team pulled it off.
The team essentially used Titan’s surface as a mirror in the experiment (known as bistatic scattering). By studying the signal that was bounced to Earth, scientists gathered information about the nature of Titan’s surface, including its composition. The same technique was used this past May to ricochet signals off of Titan’s two largest bodies of liquid – Ligeia Mare and Kraken Mare.
A second experiment during the flyby sent precision-tuned radio frequencies through Titan’s thick and dynamic atmosphere. This technique is known as radio occultation, and the data will tell scientists how temperatures vary with altitude. This is done by carefully sending a signal from Earth to Cassini, but making sure it passes through the atmosphere of Titan en route. Cassini then sends an identical signal back to Earth, also shooting it through the moon’s atmosphere. Because Cassini is a moving target, this type of measurement takes very careful timing.
Titan is a truly unique world and, like Earth, it has a thick atmosphere and bodies of liquid on its surface. However, Titan is so cold that these lakes and seas are not made of water. Instead, they are filled with liquid hydrocarbons like methane and ethane. But these hydrocarbon lakes are still part of a dynamic ‘methane cycle’ on Titan that is somewhat akin to Earth’s water cycle.
Recent studies have even identified potential waves or bubbles at the surface of Titan’s lakes. When studying Cassini observations from July of 2013, Jason Hofgartner of Cornell University and colleagues found bright features that appeared in Ligeia Mare, a sea in Titan’s northern polar region. The features then seemed to disappear in later observations.
“We suggest that these bright features are best explained by the occurrence of ephemeral phenomena such as surface waves, rising bubbles, and suspended or floating solids.” – J.D Hofgartner et al. (2014) doi:10.1038/ngeo2190
Astrobiologists study the active methane cycle and atmospheric processes on Titan in order to learn new details about similar processes on Earth. This is an area of study known as comparative planetology, and can help determine the conditions that led to habitability on our planet. For instance, the active chemistry of Titan’s atmosphere could provide important clues about the behavior of the early atmosphere of Earth.
Soaring Over Titan: Extraterrestrial Land of Lakes. Credit: NASA JPL (YouTube), Dec 12, 2013