NASA’s Cassini-Huygens spacecraft may have dramatically ended its 20-year mission to explore Saturn’s surroundings seven years ago when it plunged into the gas giant, but it’s still delivering the science bounties.
Using radar data collected by Cassini, Cornell University astronomers have gathered fresh information about the liquid ocean on Saturn’s largest moon, Titan, which is composed of hydrocarbons, a class of organic chemicals composed of carbon and hydrogen. For example, this class includes chemicals such as methane and ethane.
The team was able to analyze the composition and “bumps” of Titan’s sea, which is located near the world’s north pole. The researchers found calm seas of methane with a gentle tidal current. Not only is this something that previous studies of Titan’s seas have failed to reveal, but it also lays the foundation for future studies of the oceanic moons of the Solar System.
The Cassini data used for these new discoveries was collected using a “ballistic radar,” which involved the spacecraft pointing a radio beam at Titan that was then reflected back to Earth.
Connected: Saturn’s ocean moon Titan may not be able to support life after all
The effect of this is to polarize the surface reflection from Titan, offering views from two different vantage points. Standard radar, which saw the signal reflected back to Cassini, offered only one perspective.
“The main difference is that the bistatic information is a more complete data set and is sensitive to both the composition of the reflecting surface and its roughness,” Valerio Pojali, team member and researcher at the Cornell Center for Astrophysics and Planetary Sciences (CCAPS ), said in a statement.
Cassini launched on October 15, 1997, then took seven years to travel to the Saturn system. NASA collided Cassini with Saturn in 2017 to prevent the spacecraft from crashing into one of the gas giant’s 146 known moons.
The ballistic radar data used by Poggiali and colleagues were collected by Cassini during four flybys on May 17, June 18, and October 24, 2014, and then again on November 14, 2016. For each of these ballistic radar sets data, the surface reflections were visible when Cassini made its closest approach to 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 hydrocarbon seas depends on location and latitude. In particular, the material on the surface of the southernmost part of Kraken Mare is most efficient at reflecting radar signals.
All three of Titan’s seas appeared calm when Cassini observed them, with the spacecraft seeing waves of about 3.3 millimeters. Where the hydrocarbon seas met the shore, wave heights rose to as little as 5.2 millimeters, indicating the presence of weak tidal currents.
“We also have indications that the rivers feeding the seas are pure methane until they flow into the open liquid seas, which are richer in ethane,” Pojali added. “It’s like on Earth when freshwater rivers flow in and mix with the salt water of the oceans.”
The team said this finding fits with weather models of Saturn’s moons, 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 continues to work with data generated by Cassini during its 13 years of studying Titan. “There is a mine of data still waiting to be fully analyzed in ways that should lead to more discoveries,” he concluded. “This is only the first step.”
The team’s research was published Tuesday (July 16) in the journal Nature Communications.
