Data collected by NASA’s Cassini probe has allowed scientists to estimate the depth of Kraken Mare – the largest methane sea on Saturn’s moon Titan.
New Research published in the Journal of Geophysical Research expands our knowledge of Titan’s hydrocarbon seas, particularly Kraken Mare. This sea, about 1000 km long, is larger than all five of the Great Lakes of North America combined and contains about 80% of the moon’s surface liquids. The seas on Titan are high in methane and ethane and are comparable to liquefied natural gas on Earth.
Titan is the only moon in the solar system known to host an atmosphere. The thick, nitrogen-rich blanket that covers the moon hides a complex hydraulic system at the surface, but instead of liquid water, the rivers, lakes and seas on Titan are made of oily black methane. Titan has other curiosities too, such as gigantic dust storms, ice volcanoes, and huge dunes.
As the new research shows, the deepest parts of Kraken Mare could be more than 300 meters deep. T.the team, led by Valerio Poggiali, a research associate at the Cornell Center for Astrophysics and Planetary Science, can’t really be sure of that figure, because the radar pings used to determine the depth of the sea never reached the sea floor.
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NASA’s Cassini spacecraft orrbited Saturn from 2004 to 2017, and scientists already have studied some of the smaller seas on Titan using Cassini’s on board altimeter. On August 21, 2014, Cassini flew to within 600 miles (970 km) of Titan surface and was able to send radar pings in Kraken Mare. Interestingly, this was the same flyby that resulted in the discovery of Ligeia Mare – one “Magical” disappearing island on Titan.
Researchers from Cornell and NASA’s Jet Propulsion Laboratory have come up with a handy technique to determine the depth of Titan’s seas, measuring the differences between the time it takes for the radar to bounce off the sea surface as opposed to the sea floor. This technique helps to estimate the depth of the sea, but the researchers have to make certain assumptions about the density of liquids on Titan and how fast radio waves pass through them.
Using this technique, the team measured the depth of Moray Sinus, a northern mouth of Kraken Mare, which they found was 280 feet (85 meters) deep. The absorption rate of the radar waves suggests that the liquid in this part of the sea consists of 70% methane, 16% nitrogen and 14% ethane. The scientists expected more methane than this due to the size and location of the sea, but this discovery suggests a more uniform distribution of chemicals across the moon’s different bodies of water.
Altimeter scans performed over most of Kraken Mare were less convincing. As the authors write in the study, the NASA probe found “no evidence of signal return from the seafloor, suggesting that the liquid is too deep or absorbent for Cassini’s radio waves to penetrate.” That said, if the liquid in this part of the sea is similar in composition to the liquid found at Moray Sinus, then it must be deeper than 330 feet (100 meters) and possibly as deep as 300 meters, according to the study.
Poggiali hopes that one day a robotic submarine will be sent to Titan to explore Kraken Mare or another body of water. And in fact, he sees the new research as a step in that direction.
“Thanks to our measurements, scientists can now derive the density of the liquid with greater precision, and thus better calibrate the sonar on board the [future robotic submarine] and understand the directed currents of the sea, ”explained Poggiali at a Cornell University statement.
A conceptual plan from 2015 showed what such a mission could look like, but nothing has actually been approved on this point. That said, NASA will send a drone into the sky, called Dragonfly, to Titan, which is supposed to arrive on the moon sometime in the mid-2030s.