In the distant future, a billion miles from Earth, like a 21st-Century version of Jules Verne’s Twenty Thousand Leagues Under the Sea, a robotic, motor-less NASA submarine facsimile of Verne’s Nautilus, will probe the depths of Kraken Mare, the largest lake on Saturn’s, Earthlike moon, Titan, shrouded in a golden haze of gaseous nitrogen. This immense 1000-foot-deep body of methane is nearly the size of all five Great Lakes combined.
“The depth and composition of each of Titan’s seas had already been measured, except for Titan’s largest sea, Kraken Mare – which contains about 80% of the moon’s surface liquids,” said Valerio Poggiali, research associate at the Cornell Center for Astrophysics and Planetary Science (CCAPS) referring to findings in the data from Cassini’s T104 flyby of Titan on Aug. 21, 2014 –one of the mission’s final Titan flybys.
The spacecraft’s radar surveyed Ligeia Mare – a smaller sea in the moon’s northern polar region – to look for the mysteriously disappearing and reappearing “Magic Island.” Titan represents a model environment of a possible atmosphere of early Earth, lead-author Poggiali said, adding that In the distant future, a submarine – likely without a mechanical engine – will visit and cruise Kraken Mare.
Cassini’s Radar Reveals Depths
While Cassini cruised at 13,000 mph nearly 600 miles above Titan’s surface, the spacecraft used its radar altimeter to measure the liquid depth at Kraken Mare and Moray Sinus, an estuary located at the sea’s northern end. The Cornell scientists, along with engineers from NASA’s Jet Propulsion Laboratory, had figured out how to discern lake and sea bathymetry (depth) by noting the radar’s return time differences on the liquid surface and sea bottom, as well as the sea’s composition by acknowledging the amount of radar energy absorbed during transit through the liquid.
It turns out that Moray Sinus is about 280 feet deep, shallower than the depths of central Kraken Mare, which was too deep for the radar to measure. Surprisingly the liquid’s composition, primarily a mixture of ethane and methane, was methane-dominated and similar to the composition of nearby Ligeia Mare, Titan’s second-largest sea.
Earlier scientists had speculated that Kraken may be more ethane rich, both because of its size and extension to the moon’s lower latitudes. The observation that the liquid composition is not markedly different from the other northern seas is an important finding that will help in assessing models of Titan’s Earth-like hydrologic system.
Scientists Baffled by Origin of the Methane
Titan’s solar light – about 100 times less intense than on Earth – constantly converts methane in the atmosphere into ethane; over roughly 10 million-year periods, this process would completely deplete Titan’s surface stores, according to Poggiali.
“Thanks to our measurements,” he said, “scientists can now infer the density of the liquid with higher precision, and consequently better calibrate the sonar aboard the vessel and understand the sea’s directional flows.”
The Cornell University researchers detailed their findings in “The Bathymetry of Moray Sinus at Titan’s Kraken Mare,” published in the Journal of Geophysical Research.
Image credit: An artist’s rendering of the surface of Saturn’s largest moon, Titan. Benjamin de Bivort, debivort.org / CC BY-SA 3.0.