2024-08-09 06:00:07
Outside of Earth, the only seas known to date in the Solar System are on Titan, Saturn’s largest moon.
Using data previously collected by the Cassini probe, an international scientific team, including a researcher from the Paris Observatory – PSL, provides new insight into their composition and roughness. The results appear in the journal Nature Communications on July 16, 2024.
The Cassini mission (NASA/ESA) explored the Saturnian system for thirteen years. In particular on Titan, it revealed a fascinating diversity of landscapes: plains, mountains, large dune fields, labyrinthine terrains, rivers… And in 2007, it revealed, in the northern hemisphere, in the polar regions, the existence of three large seas of liquid hydrocarbons – named respectively Kraken Mare (the largest, with a surface area greater than that of the Caspian Sea), Ligeia Mare and Big Bag -.
The large hydrocarbon sea, Ligeia Mare, on Titan Images taken by the Radar instrument aboard NASA’s Cassini spacecraft show the evolution of a transient feature in the large hydrocarbon sea, Ligeia Mare, on Titan. NASAThese seas are accompanied by a multitude of smaller lakes. Theexploration The long-term Cassini mission has provided insight into Titan’s complex hydrological system, similar to that of Earth but dominated by the methane and ethane, rather than water, and with surface temperatures of -181°C.
Nearly seven years have passed since the end of the Cassini mission, but the colossal volume of its data has not yet been fully exploited. Many questions remain, particularly regarding the properties of the methane cycle at work on Titan, and the interactions between its polar seas and its atmosphere.
An international scientific team, led by a researcher from theUniversité from Cornell and including an astrophysicist from the Paris Observatory – PSL, analyzed a data set collected between 2014 and 2016 by an experiment bistatic radar conducted since the Cassini mission.
During its observations, the Cassini probe sent a radio signal to Titan using the antenna usually used to communicate the data collected to Earth. The liquid surfaces of the seas then acted as a mirror to reflect this signal back to Earth. By comparing the signal received to the signal sent, we can find the reflective properties (composition and roughness) of Titan’s seas. This experiment provides an overview of the composition and roughness of Titan’s liquid hydrocarbon seas, as well as some of its estuaries.
These seas exhibit different compositions, active tidal currents, wavelets, and increased roughness near estuaries and inter-basin straits.
At the time of the bistatic observations, the surfaces of Ligeia Mare, Punga Mare, and Kraken Mare were mostly smooth, with no major disturbances. The researchers found variations in the composition of the liquid between the different seas, consistent with differences in the methane-ethane mixing ratio.
Data from estuaries suggest that methane-rich rivers may have lower ethane levels than open seas. Because precipitation is mostly methane, rivers contain little ethane, which is transported and accumulated in the seas, much like rivers on Earth are composed of fresh water, and salt accumulates in the seas.
The authors estimate small-scale roughness (a few millimeters) from sea surface scattering, suggesting the presence of small surface waves. Greater roughness was concentrated in coastal areas near estuaries and interbasin straits, possibly indicating the presence of active tidal currents.
“This is the first time that we have used the bistatic radar data from the Cassini mission, even though it was acquired about ten years ago. Beyond its new scientific conclusions, this study also demonstrates the great discoveries that can be made with the multitude of still unexploited data from past space missions. Given the ecological problems facing society today, it is urgent to reduce the number of new space missions, and to finally look at the data we already have,” emphasizes Léa Bonnefoy, co-author and post-doctoral fellow at the Paris Observatory – PSL at the time of this study, concerned about the carbon impact of the instrumental resources dedicated to astronomy.
Reference:
Article titled “Surface properties of the seas of Titan as revealed by Cassini mission bistatic radar experiments“, by Valerio Poggiali (Cornell University) et al, published July 16, 2024, in Nature Communications.
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