It was years after the Cassini-Huygens spacecraft wound down its mission to Saturn, yet scientists have been deriving groundbreaking findings from the treasure trove of data. Now, a group of astronomers from Cornell has published improved knowledge of the mysterious liquid hydrocarbon seas lying near the north pole of Titan, Saturn’s courtesy moon.
The research team, using the bistatic radar experiments, was able to dissect and estimate the composition and surface roughness of the seas on Titan where monostatic radar data could not. This opens the way for full-fledged examinations in the future about the seas on Titan, using the data from Cassini.
Valerio Poggiali, a research associate at the Cornell Center for Astrophysics and Planetary Science (CCAPS), spearheaded the study, which was published in Nature Communications. Co-authors include Alexander Hayes, the Jennifer and Albert Sohn Professor and director of CCAPS, Philip Nicholson, a professor in the Department of Astronomy, and Daniel Lalich, a CCAPS research associate.
Bistatic radar experiments involve aiming a radio beam from the spacecraft at Titan, where it reflects toward a receiving antenna on Earth. This method provides a more complete dataset, sensitive to both the composition and roughness of the reflecting surface. “The bistatic information is a more complete dataset, and is sensitive to both the composition of the reflecting surface and its roughness,” Poggiali explained.
According to Nicholson, “The successful execution of a bistatic radar experiment requires exquisite choreography between the scientists who design it, Cassini mission planners and navigators, and the team who collects the data at the receiving station.”
The team worked with four bistatic radar observations acquired in Cassini flybys occurring in the 2014 and 2016 time periods. Their goal was the three large polar seas on Titan: Kraken Mare, Ligeia Mare, and Punga Mare. Their findings revealed variations in the composition of surface layers of the hydrocarbon seas by latitude and proximity to rivers and estuaries. It was interesting that the highest dielectric constant, which is an indication of better reflection toward the emitter, was returned from the southernmost part of the Kraken Mare.
Researchers also determined that all three seas were generally placid during both flybys, with surface waves never exceeding 3.3 millimeters. Slightly higher roughness levels, up to 5.2 mm, were apparent nearer the coasts, estuaries, and interbasin straits, which may reflect tidal currents.
Poggiali said the rivers going into the seas seem to be mainly methane until they mix with the more ethane-rich open seas, much like Earth’s freshwater rivers mix with salty ocean water. This fits neatly with meteorological models for Titan that predict the rain from its skies is nearly pure methane with a few percent of ethane and other hydrocarbons.
“There is a mine of data that still waits to be fully analyzed in ways that should yield more discoveries,” Poggiali said. “This is only the first step.”
The research was funded by NASA and the Italian Space Agency. Contributors included the Università di Bologna, the Observatoire de Paris, NASA’s Jet Propulsion Laboratory, the California Institute of Technology, the Johns Hopkins University Applied Physics Laboratory, and the Massachusetts Institute of Technology.
As scientists continue to mine Cassini’s rich data, the mission’s heritage lives on, providing new insights about the alien world of Titan and beyond.