July 17, 2024: Bistatic Radar Experiments Allow Us To Evaluate The Roughness And The Composition Of The Pools Found In The North Polar Region Of Titan
A new study entitled "Surface properties of the seas of Titan as revealed by Cassini mission bistatic radar experiments", proposed by a team of researchers involving Valerio Poggiali, Alexander Hayes and Philip Nicholson and published in Nature Communications on July 16, 2024 reveals that bistatic radar experiments involving the data acquired from the Cassini spacecraft and from a receiving antenna on Earth regarding the land of lakes and seas in the north polar region of Titan bring significant clues upon the nature and the roughness of the pools in the area. Planetologists had already determined that the lakes and seas of Saturn's largest moon appeared remarkably quiet or smooth during the long mission of the Cassini probe in the Saturn System from 2004 to 2017. The composition and the roughness of the lake or sea can vary depending on the latitude, the area or the season. The new research work reveals or suggests a difference in the composition of the liquid between the rivers, the estuaries, the lakes or the seas found in the north polar region of the giant moon. Several types of molecules or elements can be encountered in those exotic pools.
The Cassini-Huygens mission in the Saturn System has allowed us to collect a huge amount of information regarding Saturn, Titan and the other major moons of the Gas Giant. The Huygens probe had revealed a diverse landscape with bright hills, a brown or dark plain and dark channels that may represent drainage channels related to meteorological phenomena. The radar views as well as the infrared or near-infrared views obtained from the Cassini spacecraft have clearly revealed the presence of lakes, seas or rivers in the high latitudes of each hemisphere of Titan. In the harsh environment of that intriguing world, methane, ethane or propane can be found in their liquid form on the surface. Prior to the Cassini-Huygens mission in the Saturn System, planetologists had anticipated the potential presence of lakes, seas or oceans dominated by methane or ethane. Some researchers had imagined that the relatively dark areas which mark a sharp contrast with relatively bright areas in the low or middle latitudes could represent seas or oceans of methane or ethane. The radar views have clearly shown that those relatively dark areas are in fact dominated by linear and parallel dunes that extend over long distances.
The first active pool of liquids was identified in the high latitudes of the southern hemisphere during the Summer season in the southern hemisphere. That pool whose shape looks like the shape of a foot is known as Ontario Lacus. Later, we found a land of lakes, seas and rivers in the northern hemisphere. Kraken Mare, Ligeia Mare and Punga Mare represent the major pools of that region in the high latitudes of that hemisphere. Is the composition of those pools relatively uniform ? Are there differences in their composition or in their dynamics depending on the latitude, the area or the season ? Bistatic radar experiments bring a new light regarding the dynamics and the composition of those pools. They allow the researchers to evaluate the effective relative dielectric constant and the small-scale roughness of the surface of the lake or sea. Bistatic radar experiments allow better analyses of the composition and the dynamics of the pools, lakes or estuaries compared to the usual analyses based on monostatic radar data. The team of scientists managed to identify relatively significant variations in effective dielectric constant or in the composition of the liquid depending on the latitude. The concentration of methane and ethane will tend to vary depending on the area.
The outcome of the study regarding the estuaries reveals that the concentration of methane in the liquid tends to be higher in estuaries than in the open lakes or seas. That configuration implies the presence of methane-rich rivers connected to pools containing a lower concentration of methane (CH4) and a higher concentration of ethane (C2H6). The planetologists were in a position to evaluate the potential height of the waves in the pool. The small-scale roughness is evaluated at a level of a few millimeters on the basis of the almost purely coherent scattering from the surface of the pool. That configuration implies the presence of capillary waves. That level of roughness is clearly observed near estuaries and inter-basin straits. That's a configuration which implies active tidal currents. A parallel can be drawn between the variations in the composition of the rivers and the seas or oceans on Earth. The rivers of Titan unveil a high concentration of methane or "fresh methane" and the rivers of the Earth unveil fresh water or pure water. The composition of the major pool on Titan is more diverse with a higher concentration of ethane. That's also the case for the seas or oceans on Earth which contain salty water.
Titan evolves in an environment where water ice is everywhere. The ingredients of the meteorology and of the hydrology of the Opaque Moon appear clearly exotical to us. That's why the chemistry and the dynamics of the rivers, of the lakes, of the seas, of the soil and of the atmosphere of that intriguing moon are likely to tell us a lot regarding the working of nature and the chemistry of hydrocarbons and organics. Clouds can develop and engender rain on Titan like on Earth but the clouds of Titan will tend to be dominated by methane or ethane. Water can only appear in its solid form on the surface of that world where the environmental temperature evolves around -179 degrees Celsius, -290 degrees Fahrenheit or 94 Kelvin. What type of chemical interactions can take shape in a pool dominated by liquid methane or liquid ethane ? Can a prebiotic chemistry take shape and develop even if the chemical interactions are very slow compared to the typical chemical interactions of our seas or oceans ? The lakes and seas of methane or ethane of that world clearly represent a natural laboratory to study the chemistry of hydrocarbons and organics in a harsh environment.
The atmosphere of Titan can also be fruitful in terms of chemistry. There is a global haze that prevents us from discerning the surface from outer space in the visible spectrum. That haze is closely related to the action of ultraviolet light from the Sun that engenders complex interactions between ions, elements, molecules or radicals in the upper atmosphere. Heavier molecules will tend to fall due to their weight. A type of snow rich in hydrocarbons or organics can reach the surface to engender dunes, to form a dark or brown mud or sludge or can reach the seas, lakes or rivers to feed their chemistry. The analysis of the chemistry and of the dynamics of rivers, lakes and seas on Titan is clearly a challenge due to the relatively limited amount of key data we have at our disposal today. We managed to gather new clues regarding the dynamics and the chemistry of those pools found in the high latitudes of the northern hemisphere thanks to bistatic radar experiments. Bistatic radar experiments allow researchers to study the radio beam emitted by the Cassini spacecraft, reflected on the surface of Titan and received by an antenna on our own planet. That configuration implies two perspectives, one from the spacecraft and one from our antenna on Earth.
The bistatic radar experiment implies two perspectives whereas the monostatic radar experiment only implies one perspective, the perspective from the Cassini spacecraft. Bistatic radar experiments are clearly better than monostatic radar experiments. They imply a perfect coordination between the researchers, the planners and the navigators of the Cassini mission and the scientists or engineers who collect the data at the receiving antenna on Earth. Bistatic radar information informs us upon the composition, the roughness and the reflecting surface of the pool. The study of the planetologists was performed on the basis of four bistatic radar observations carried out with the Cassini spacecraft during four flybys in 2014 and in 2016. The first flyby was performed on May 17, 2014, the second flyby was performed on June 18, 2014, the third flyby was performed on October 24, 2014 and the fourth flyby was performed on November 14, 2016. The surface reflections were captured as the probe neared its closest approach to the giant moon (ingress) and as it moved away (egress). The researchers focused their attention on the analysis of Kraken Mare, Ligeia Mare and Punga Mare on the basis of the egress observations.
The composition will tend to be related to the factor of latitude and to the factor of location. The team found that the southernmost part of Kraken Mare reveals the highest dielectric constant. The dielectric constant of water on the Blue Panet is particularly high since its value is around 80 compared to only around 1.7 for the ethane and methane pools of Saturn's largest moon. Thus, water is very reflective compared to methane and ethane. The planetologists also found that the three major pools of the north polar region were relatively quiet at the time of the observations with waves no larger than 3.3 millimeters. Coastal regions, estuaries and interbasin straits appeared rougher with waves that could reach a height of 5.2 millimeters. That's a sign of tidal currents in those particular areas. Those rivers, lakes or seas are clearly exotical and mysterious but the study of those rivers or pools reveals similarities with the rivers, seas or oceans on Earth. The key molecule of the meteorology of the Earth is water whereas the key molecule of the meteorology of Titan is methane. The sea on Earth is mainly composed of a mixture of water and salt (NaCl) whereas the major lakes or seas of Titan will tend to be composed of a mixture of methane and ethane that can appear in its liquid form in that harsh environment. Dissolved nitrogen may also be present in those exotic rivers, lakes or seas.
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The image above represents a portion of a radar swath of Saturn's largest moon obtained from the Cassini spacecraft during the T30 Flyby of May 12, 2007. The radar swath revealed a portion of Kraken Mare, the major pool of Titan found in the northern hemisphere in its high latitudes. Each side of the image represents approximately 100 kilometers. The file name of the original view is BIUQI61N250_D131_T030S01_V02.jpg. A particularly irregular shoreline as well as many islands can be clearly discerned in the view. Erosional processes related to the liquid must be relatively strong in the area. Credit for the original view: NASA/JPL/Cassini Radar Team/Jason Perry. Montage credit: Marc Lafferre, 2024. |
- To get further information on that news, go to: https://news.cornell.edu/stories/2024/07/new-analysis-cassini-data-yields-insights-titans-seas and https://www.nature.com/articles/s41467-024-49837-2 .