NASA’s Cassini-Huygens spacecraft may have dramatically ended its 20-year mission to explore Saturn’s neighborhood seven years ago when it plunged into the gas giant, but it continues to deliver scientific results.
Using radar data collected by Cassini, astronomers at Cornell University have gathered new information about the liquid ocean on Saturn’s largest moon Titan, which is composed of hydrocarbons, a class of organic compounds made up of carbon and hydrogen. This class includes, for example, compounds such as methane and ethane.
The team was able to analyze the composition and “roughness” of Titan’s sea, located near the planet’s north pole. The researchers discovered calm methane seas with a weak tidal current. Not only was this phenomenon not revealed by previous examinations of Titan’s seas, but it also lays the foundation for future research on the oceanic moons of the solar system.
The Cassini data used to make these new discoveries was collected using “ballistic radar,” which involved the spacecraft directing a radio beam at Titan that was then reflected back to Earth.
Related: Saturn’s Ocean Moon Titan May Not Be Able to Support Life After All
The effect of this situation is the polarization of the reflection from Titan’s surface, which offers views from two different perspectives. The standard radar that saw the signal reflected back to Cassini offered only one perspective.
“The main difference is that bistatic information is a more complete dataset and is sensitive to both the composition of the reflecting surface and its roughness,” team member Valerio Poggiali, a researcher at the Cornell Center for Astrophysics and Planetary Science (CCAPS), said in a statement.
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a dark orange/brown planet is opened to show different layers.
A diagram showing the interior of Saturn’s moon diagram, including its deep ocean. (Photo credit: AD Fortes/UCL/STFC)
The Cassini spacecraft was launched on October 15, 1997, and took seven years to reach the Saturnian system. NASA sent Cassini into a collision with Saturn in 2017 to prevent the spacecraft from hitting one of the gas giant’s 146 known moons.
The ballistic radar data used by Poggiali and his colleagues were collected by Cassini during four flybys on May 17, June 18, and October 24, 2014, and again on November 14, 2016. For each of these ballistic radar data sets, the surface reflections were observed as Cassini approached Titan and then again as it moved away from the moon.
The researchers examined observations of three of Titan’s polar seas: Kraken Mare, Ligeia Mare, and Punga Mare. They found that the composition of the surface layers of the hydrocarbon seas depended on location and latitude. In particular, materials on the surface of the southernmost part of Kraken Mare were the most effective at reflecting radar signals.
A dark sphere bounded by a thicker yellow-brown ring at the north pole of the sphere
Titan, Saturn’s largest moon, as seen by the Cassini space probe. (Photo credit: NASA/JPL-Caltech/Space Science Institute)
Titan’s three seas appeared calm when Cassini observed them, with the probe seeing waves of about 3.3 millimeters (0.13 inches). Where the oil seas met the coast, wave heights rose to just 5.2 millimeters (0.20 inches), indicating the existence of weak tidal currents.
“We also have indications that the rivers that feed the seas are pure methane until they flow into the open liquid seas, which are richer in ethane,” Poggiali added. “It’s like on Earth, when freshwater rivers flow and mix with the salt water of the oceans.”
The team said the finding fits with weather models of the Saturnian moon, which have predicted that the rain that falls on Titan is mostly methane, with small amounts of ethane and other hydrocarbons.
Poggiali added that the team is continuing to work with data generated by Cassini during its 13-year study of Titan. “There is a wealth of data that is still waiting to be fully analyzed in a way that can lead to new discoveries,” he said. “This is just the first step.”
The team’s research was published Tuesday (July 16) in the journal Nature Communications.
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