The latest data analysis from the Cassini-Huygens space probe has further illuminated the mysterious seas of Titan, Saturn’s largest moon.
Bistatic radar returns from the moon are providing scientists with greater insight into Titan’s northern seas behavior and composition, according to a new study spearheaded by Cornell University, released on Tuesday in the journal Nature Communications.
Collecting Data on Titan
The Cassini-Huygens mission involves a space probe launched in an international cooperative effort between NASA, the European Space Agency, and the Italian Space Agency. Its goal is to collect data regarding the planet Saturn itself, as well as its surrounding rings and moons.
Two implements were used to conduct the mission: the Cassini space probe orbiting Saturn and the Huygens lander that set down on Titan. Cassini orbited the planet from 2004 until it burned up in Saturn’s atmosphere in 2017. Huygens landed on Titan in January 2005, but contact was lost a little over an hour after it touched down due to a communications problem not identified until after launch.
Novel Data Collection Methods
The difference between the new bistatic method of observation and the previous monostatic method is that the new data comes from a polarized reflection. This means that the reflection is viewed from two perspectives, both the sending spacecraft and a receiver back on Earth. Previous monostatic data was returned only to the spacecraft itself.
Valerio Poggiali, lead author of the new study, says the result of the bistatic method “is a more complete dataset and is sensitive to both the composition of the reflecting surface and to its roughness.” While the bistatic data set does provide dynamic new information, the old mono static data is still relied upon for context. Even this new data set has some limitations, as the radar returns are limited to the surface level of bodies and are incapable of providing depth-sounding information.
The data collection for the recent study actually began a decade ago, as the probe collected measurements when it came into its closest proximity to Titan and again when it moved away. These ingresses and egresses occurred on May 17, June 18, and October 24, 2014, and over two years later on November 14, 2016. The team focused on data collected during the egress portions of the flybys, as only on the egress phase did the radar return cross one of the bodies that the team was honed in on, the Kraken Mare, Ligeia Mare, and Punga Mare polar seas.
The Seas of Titan Show to be Quite Different Than Those of Earth
The differences that emerged between the seas corresponded to the sea’s latitude and location. Proximity to other features, such as rivers and estuaries, impacted the seas’ composition. Titan’s tranquil seas only show minor 3.3-millimeter waves, raising to 5.3 mm near regions where bodies of water meet, such as coasts, estuaries, and interbasin straits. This suggests the existence of tidal currents on the moon. On Earth, we typically measure waves in meters, not millimeters. So, while there is some variation, the surface is remarkably calm from our perspective.
Another significant variance with Earth is the dialectic constant of Titan’s liquid bodies. Dielectric constant refers to the ability of a material to store electrical energy instead of conducting it. The water bodies of Earth have a high dielectric constant of about 80. In contrast, the methane seas of Titan have a dramatically lower value of around 1.7, falling even lower in rougher coastal areas and estuaries. That is only a bit higher than air on Earth, which registers about a 1. This impacts the bistatic radar returns because a higher value leads to a more accurate reading from a stronger signal.
The Data Meets Our Predictions, But Discoveries Still Lay Ahead
Although their composition appears to be much different, the seas on Titan appear to be behaving quite similarly to the ones on Earth in certain other respects. On Earth, we are dealing with water and salt, but the methane and ethane existent in liquid form on Titan appear to flow quite similarly. Earth’s freshwater streams pour into salty oceans. On Titan, pure methane rivers flow into oceans mixed with ethane.
The new findings “fit nicely with meteorological models for Titan,” according to the study’s co-author, Philip D. Nicholson, an astronomy professor at Cornell. As predicted, it appears that Titan receives a rain comprised of methane and nitrogen.
However, the team has not concluded its work. Poggiali says, “This is only the first step.” With 13 years in orbit, Cassini has collected a mountain of data that still needs to be sifted. In short, our overall understanding of Titan and its seas is still only beginning.
The new study was made possible by international backing from NASA and the Italian Space Agency. While Cornell led the effort, contributors included the Massachusetts Institute of Technology, California Institute of Technology, NASA Jet Propulsion Laboratory, and Università di Bologna.
The study, titled “Surface Properties of the Seas of Titan as Revealed by Cassini Mission Bistatic Radar Experiments,” appeared in Nature Communications on July 16, 2024.
Ryan Whalen is a writer based in New York. He has served in the Army National Guard and holds a BA in History and a Master of Library and Information Science with a certificate in Data Science. He is currently finishing an MA in Public History and working with the Harbor Defense Museum at Fort Hamilton, Brooklyn.