Cassini probe explores some of the secrets of the seas of Saturn's moon Titan

NASA's Cassini-Huygens spacecraft ended its 20-year mission to explore Saturn's vicinity seven years ago, but it's still making more scientific discoveries.

Using Cassini radar data, Cornell astronomers have gathered new information about the liquid ocean of Saturn's largest moon, Titan, which is made up of hydrocarbons, a class of organic chemicals made up of carbon and hydrogen. For example, this class includes chemicals such as methane and ethane.

The team was able to analyze the composition and "roughness" of Titan's sea, which is located near the moon's north pole. The scientists found calm seas of methane gas with a gentle tidal current.

Titan is the largest of the 146 known moons orbiting Saturn, and it captivates scientists and space enthusiasts alike with its unique features and potential to harbor life.

The Cassini data used to achieve these new results were collected by "ballistic radar," which involves the spacecraft pointing a radio beam at Titan that is then reflected back toward Earth.

The effect of this is to polarize the surface reflection from Titan, which provides views from two different perspectives.

Ballistic radar data were collected during four flights on May 17, June 18, and October 24, 2014, and again on November 14, 2016.

For each of these ballistic radar data sets, surface reflections were observed as Cassini approached Titan at its closest point, and then again as it moved away from the moon.

The team 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 depends on location and latitude.

In particular, the materials on the surface of the southern part of Kraken Mare were the most efficient at reflecting radar signals.

Titan's three seas appeared calm when Cassini observed them, with the spacecraft seeing waves about 3.3 millimeters high. Where the hydrocarbon seas met the coast, the waves rose to just 5.2 millimeters, indicating weak tidal currents.

“We 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,” said Valerio Poggiali, a researcher at the Cornell Center for Astrophysics and Planetary Sciences (CCAPS). “It’s like on Earth when freshwater rivers flow and mix with saltwater in the oceans.”

The team said the discovery fits with meteorological models of Saturn's moon, which predicted that Titan's rain is mostly methane, with small amounts of ethane and other hydrocarbons.

Poggiali added that the team continues to work with the data Cassini has generated over its 13 years of studying Titan. “There is a mine of data still waiting to be fully analyzed in ways that will lead to more discoveries,” he concluded. “This is just the first step.”

Cassini was launched from Cape Canaveral, Florida, on October 15, 1997, and spent seven years traveling to Saturn, followed by 13 years orbiting the planet. During that time, it shared the wonders of Saturn and its family of icy moons with Earth before running out of fuel, after 20 years in space and ending its mission by burning up inside the planet’s atmosphere on September 15, 2017, after sending all the data back to our planet.

The research paper was published in the journal Nature Communications.