Saturn’s moon Titan was explored by NASA’s Cassini spacecraft between 2004 and 2017. Although Cassini revealed much about this Earth-like world, its radar observations provided limited information about Titan’s liquid hydrocarbon oceans: Kraken, Ligeia, and Punga Mare. New paper In the journal Nature CommunicationsCornell University researcher Valerio Poggiali and his colleagues reported the results of their analysis of data from the Cassini radar experiment on Titan’s polar oceans.

“The Cassini spacecraft explored Saturn’s largest moon, Titan, between 2004 and 2017, revealing an Earth-like world with a strange yet very familiar diversity of surface morphologies formed by a methane-based hydrological system operating in a dense nitrogen atmosphere,” said Dr Poggiali and his co-authors.

“Winds in the lower atmosphere move the sediments, forming the vast sand dunes that encircle Titan’s equator.”

“At mid-latitudes, flat, relatively featureless plains form the transition between the eolianite-dominated equator and the lacustrine-dominated poles.”

“In the polar regions, large oceans and small lakes of liquid hydrocarbons dominate the landscape.”

“The channels created by precipitation drain into the ocean, forming estuaries and sometimes deltas and other familiar coastal deposits.”

“Cassini has revealed much about Titan, but this discovery raises even more questions.”

For the study, scientists used data from four bistatic radar observations collected by Cassini during four flybys in 2014 (May 17, June 18, and October 24) and 2016 (November 14).

For each, surface reflections were observed when the probe was closest to Titan (approach) and when it was moving away (exit).

The authors analyzed data from outflow observations of Titan’s three large polar oceans: Kraken Mare, Ligeia Mare, and Punga Mare.

“In a bistatic radar experiment, a spacecraft directs a radio beam towards a target, in this case Titan, where the beam is reflected towards a receiving antenna on Earth,” the researchers explained.

“This surface reflection is polarized, which means it provides information gathered from two independent perspectives, as opposed to the perspective provided by monostatic radar data, where the reflected signal is sent back to the spacecraft.”

“The main difference is that the bistatic information is a more complete data set and is sensitive to both the composition of the reflective surface and its roughness.”

The team found that the composition of the ocean’s surface layers of hydrocarbons varies depending on latitude and location (for example, near rivers or estuaries).

Specifically, the southernmost parts of Kraken Mare exhibit the highest dielectric constant, a measure of a material’s ability to reflect radio signals.

For example, water on Earth is highly reflective and has a dielectric constant of about 80, while Titan’s ethane and methane oceans have a dielectric constant of about 1.7.

The researchers also determined that ocean conditions in all three areas were fairly calm during the flyby, with surface waves measuring less than 3.3 mm.

Slightly higher levels of roughness, up to 5.2 mm, were found in coastal areas, near estuaries and straits, which could be an indication of tidal currents.

“There are also indications that the rivers that feed the oceans are pure methane until they flow into the open ocean liquid, which is rich in ethane,” Dr Poggiali said.

“It’s the same as when freshwater rivers flow into the saltwater of the ocean on Earth and mix together.”

“This fits well with weather models of Titan, which predict that the ‘rain’ falling from Titan’s skies is almost pure methane, with traces of ethane and other hydrocarbons,” said Professor Philip Nicholson of Cornell University.

“Further studies of the data Cassini has collected during its 13-year exploration of Titan are already underway.”

“There’s still a mountain of data waiting to be fully analyzed in a way that will lead to further discoveries. This is just the first step.”

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V. Poggiali others2024. Surface characteristics of Titan’s ocean as revealed by the Cassini bistatic radar experiment. Nat Community 15, 5454; doi: 10.1038/s41467-024-49837-2

This article is a version of a press release provided by Cornell University.