New analysis of Cassini data provides insight into Titan’s seas

A new study of radar experiment data from the Cassini-Huygens mission to Saturn has provided new insights into the composition and activity of liquid hydrocarbon seas near the north pole of Titan, the largest of Saturn’s 146 known moons. .

Using data from several bistatic radar experiments, a research team led by Cornell University was able to separately analyze and estimate the composition and roughness of Titan’s sea surfaces, something that previous analyzes of monostatic radar data had not. able to reach. This will help pave the way for future combined examinations of the nature of Titan’s seas using Cassini data.

Valerio Poggiali, a research associate at Cornell University, is the lead author of “Surface Properties of Titan’s Seas as Revealed by the Cassini Mission’s Bistatic Radar Experiments,” which was published July 16 in Nature Communications.

A bistatic radar experiment involves aiming a radio beam from the spacecraft at the target – in this case Titan – where it is reflected back to the receiving antenna on Earth. This surface reflection is polarized – meaning it provides information collected from two independent perspectives, as opposed to that provided by monostatic radar data, where the reflected signal is returned to the spacecraft.

“The main difference,” said Poggiali, “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.”

The current work used four bistatic radar observations collected by Cassini during four flybys in 2014—on May 17, June 18, October 24, and in 2016—on November 14. For each, surface reflections were observed as the spacecraft made its closest approach to Titan (input), and again as it moved away (output). The team analyzed data from observations of the outflow of Titan’s three large polar seas: Kraken Mare, Ligeia Mare and Punga Mare.

Their analysis found differences in the composition of the surface layers of hydrocarbon seas, depending on latitude and location (near rivers and estuaries, for example). Specifically, the southernmost part of Kraken Mare shows the highest dielectric constant – a measure of a material’s ability to reflect a radio signal. For example, water on Earth is highly reflective, with a dielectric constant of about 80; Titan’s ethane and methane seas are about 1.7.

The researchers also determined that all three seas were mostly calm at the time of the flights, with surface waves no larger than 3.3 millimeters. A slightly higher level of roughness – up to 5.2 mm – was detected near coastal areas, estuaries and interbasin straits, possible indicators of tidal currents.

“We also have indications that the rivers that feed the seas are pure methane,” Poggiali said, “until they flow into the liquid open seas, which are richer in ethane. It’s like on Earth, when freshwater rivers pour out and mix with the salty water of the oceans.

“This fits well with meteorological models for Titan,” said co-author and professor of astronomy Philip Nicholson, “which predict that the ‘rain’ falling from its sky is likely to be almost pure methane, but with small amounts of ethane. and other hydrocarbons”.

Poggiali said more work is already underway on the data Cassini generated during its 13-year examination of Titan. “There is a mine of data still waiting to be fully analyzed in ways that should yield more discoveries,” he said. “This is just the first step.”

Other contributors to this work are from the Università di Bologna; Observatoire de Paris; NASA’s Jet Propulsion Laboratory (JPL); California Institute of Technology; and the Massachusetts Institute of Technology.