Saturn’s moon Titan sports phantom hydrocarbon lakes

Three lakes on Saturn’s moon Titan have up and vanished.

Researchers previously had seen evidence that Titan’s lakes, filled with hydrocarbons like methane and ethane, shrink during the moon’s summer. But a new analysis of data from the defunct Cassini spacecraft offers the first glimpse of lakes completely disappearing off the face of the moon. The discovery of these phantom lakes offers new insight into the only other solar system body known to host a hydrological cycle, researchers report online April 15 in Nature Astronomy.

Planetary scientist Shannon MacKenzie and colleagues uncovered the disappearing lakes by comparing Cassini observations from two different seasons of Titan’s year, which lasts 29.5 Earth years. In the midst of Titan’s winter in 2006, Cassini’s radar observations indicated that all three lakes were filled with liquid. But when Cassini’s infrared cameras were trained on the lakes in 2013, during the moon’s spring, all three had dried up.

“The fact that they just do not look like liquids at all to the [infrared] instruments is so weird,” says MacKenzie, of Johns Hopkins University Applied Physics Laboratory in Laurel, Md. These lakes may have been extremely shallow, perhaps just centimeters deep, and evaporated or seeped into the ground as winter turned to spring.

Not all of Titan’s lakes are so fragile. Planetary scientist Marco Mastrogiuseppe of Caltech and colleagues examined Cassini radar data from 2017 and found that some of the moon’s other lakes may be more than 100 meters deep. The team reported these results in the same issue of Nature Astronomy.

“We can’t really say from Cassini data” whether the phantom lakes are gone for good or will reemerge next winter, MacKenzie says. To fully understand the phantom lake effect, “what we would really need in the future is some kind of Titan orbiter — something like what we have at Mars with the [Mars Reconnaissance Orbiter], or the Lunar Reconnaissance Orbiter on the moon, giving us repeat observations.”