January 9, 2024: The Famous "Magic Islands" Of Titan May Represent Relatively Porous Organic Glaciers According To A New Study
A new research work entitled "The Fate of Simple Organics on Titan's Surface: A Theoretical Perspective", published in Geophysical Research Letters on January 4, 2024 and proposed by a team of researchers involving Xinting Yu, Yue Yu, Julia Garver, Xi Zhang and Patricia McGuiggan suggests that the famous "Magic Islands" of Titan may represent relatively porous organic glaciers. The Magic Islands had been identified in 2014 thanks to radar data taken from the Cassini spacecraft during its orbital dance in the system of Saturn and its numerous moons. In the land of lakes and seas found in the high latitudes of the northern hemisphere of Saturn's largest moon, transient islands seem to be present from time to time. During the long mission of the Cassini orbiter in the Saturn System, from 2004 to 2017, we had obtained a multitude of radar images and we have been in a position to perform an analytical work regarding the evolution of the lakes, seas or rivers found in the high latitudes of the Opaque Moon. In Ligeia Mare or Kraken Mare, new bright patches had appeared inside the pools and they had progressively vanished in just a few weeks.
What do those enigmatic bright patches represent ? Are they really islands ? Do they represent an area of strong waves ? Do they represent a field of bubbles related to cryovolcanic features ? Are they transient icebergs ? Are they related to a biological system within the pool ? The debate is far from being over and several hypotheses can be put forward. In the new study proposed by UTSA professor Xinting Yu and her collaborators, the hypothesis that the Magic Islands could in fact represent relatively porous organic glaciers is rigorously considered. The floating chunks of porous, icy organic solids may be closely related to atmospheric phenomena. There is a complex chemistry in the atmosphere of that giant moon. The haze of the atmosphere is closely related to the light from the Sun. Ultraviolet radiations engender various chemical reactions in the upper atmosphere. The atmosphere of Titan is in fact a soup of elements, molecules or radicals where relatively complex molecules can emerge and fall toward the surface. The atmosphere of that orange world is clearly remarkable because it may look like the atmosphere of the Early Earth. Like the atmosphere of the Blue Planet, the atmosphere of Titan is dominated by molecular nitrogen.
Most moons in the Solar System are devoid of any atmosphere and Titan represents an exception. The moon is heavy enough and cold enough to retain a significant atmosphere. That's not the case for Ganymede, the largest moon in the Solar System. Triton, the largest moon of Neptune, contains a thin atmosphere dominated by molecular nitrogen. That's also the case for Pluto, the largest Dwarf Planet in the Solar System. The infrared or near-infrared images and the radar views captured from the Cassini orbiter have clearly revealed that there is a complex meteorological cycle on Titan. Several types of clouds can form and develop. The nature of the Titanian clouds appears very different from the nature of the clouds we regularly encounter on Earth. The clouds of Titan are not made of water vapor or water ice. The clouds of Titan are generally composed of hydrocarbons like methane or ethane. Methane appears to be the second most abundant gas in the atmosphere of the giant moon. To a certain extent, the meteorological cycle of Titan involving the methane molecules (CH4) looks like the meteorological cycle of the Earth involving the water molecules (H2O).
In the study of the research group, the planetologists analyze the potential mechanisms that lead to the formation and the development of the molecules that are heavy enough to reach the ground or the surface of the lakes, seas or rivers. The scientists suggest that simple hydrocarbons or organics like triple-bonded hydrocarbons, benzene or nitriles can fall to the surface as solids. They note that a few molecules can appear in their liquid phase when they fall to the surface. They also suggest that ethylene (C2H4) will remain in the form of gas. Can the solids falling from the atmosphere accumulate to form icebergs or icy chunks floating on the surface of the pool ? The team of planetologists suggests that this configuration can be envisaged if the glacier is porous enough. The chunk, the iceberg or the glacier will tend to float if its level of porosity is high enough. The first step is to determine the potential composition of the potential glaciers representing the bright features of the Magic Islands in the radar views from the Cassini spacecraft. The hypothetical chunks or glaciers can be composed of hydrogen cyanide ices for instance. The second step is to determine the potential composition of the lake or sea. One can envisage an ethane-rich pool.
The team of Xinting Yu was in a position to determine, on the basis of the principles of buoyancy, that flotation for the chunk, for the iceberg or for the glacier can be obtained if the level of porosity of the material is between 25 percent and 60 percent or if there is a capillary force-induced buoyancy in a configuration in which the icy material is composed of hydrogen cyanide (HCN) and in which the pool is rich in ethane (C2H6). If the level of porosity is too low or if the mean density of the material is too high, the glacier, the chunk or the iceberg will tend to sink to fuel the sediments of the lake or sea. The researchers have been in a position to evaluate the level of stability of the presumed chunks or the potential lifespan of those exotic glaciers. Therefore, they are in a position to advance that a flotation phenomenon related to a relatively high level of porosity can exist for millimeter-sized and larger sediments. The Magic Islands observed from the Cassini orbiter could have been transient icebergs, floating chunks or glaciers generated by an accumulation process of those types of compounds or sediments. To a certain extent, the structure of those presumed exotic icebergs can be compared to a sponge.
The composition of the lakes or seas on Titan must be dominated by methane or ethane. Some pools may be richer in methane and some pools may be richer in ethane. Methane, ethane or propane can appear in their liquid form on the surface of that intriguing world. The configuration may be more complex than the configuration of our oceans, seas, lakes or rivers on Earth in terms of interactions between the various elements or compounds of the pool or river. Several layers of liquid can be imagined in the pools of Titan. One can imagine that the denser liquid will be found beneath the liquid whose density is lower. The composition of the lakes or seas on Titan may vary depending on the area or depending on seasonal factors. The pools may contain mixtures of methane, ethane and dissolved nitrogen. The mean density of the most simple hydrocarbons like methane and ethane is particularly low. The mean density of pure liquid methane is much lower than that of pure liquid water so that any iceberg evolving in a lake or sea on a world like Titan must have a particularly low mean density to avoid sinking. The composition and the structure of the chunk must be considered to evaluate its buoyancy.
Xinting Yu and her team advance that the pools are saturated with organic compounds so that the organic clumps reaching the lake or sea will not tend to dissolve, in a relatively short time, in the liquid environment. The phenomenon of capillary forces and the phenomenon of porosity have been analyzed by the group of researchers. The scientists came to the conclusion that the phenomenon of capillary forces had to be ruled out because liquid methane and liquid ethane have a low surface tension and because most of the frozen solids reaching the pool were too dense or not light enough for capillary forces alone to make the Magic Islands possible. The major factor for Xinting Yu and her team turns out to be the level of porosity. If the icy clumps are relatively big and contain the right concentration of holes and narrow tubes, exotic icebergs or chunks floating in the pool can be imagined even if the liquid dominated by methane progressively infiltrates the chunk or iceberg. In that configuration, the chunk can float for a relatively long time until it eventually sinks to fuel the sediments of the lake or sea. The researchers advance that the organic clumps must accumulate to form bigger structures that can become icebergs or glaciers.
Phenomena related to capillary force will tend to take a longer time to make the larger chunks sink than the smaller chunks. The Magic Islands were found relatively close to the shore so that landslides or cryovolcanic events could have engendered those transient bright patches within the lake or sea. The radar views reveal that relatively large bright patches had engendered several smaller bright patches in a matter of days or weeks. Therefore, the Magic Islands may have progressively dissolved over time. The surface dynamics of the lakes or seas of Titan must be relatively quiet or limited since the radar views obtained from the Cassini orbiter suggest a remarkably smooth surface within the lakes or seas. The impressive smoothness of the lakes or seas may be related to the presence of a thin layer of frozen solids evolving above the liquid so that the pool may appear to be almost as smooth as a mirror. That's not what had been anticipated or predicted by other researchers prior to the start of the Cassini-Huygens mission in the Saturn System in 2004. Giant waves of methane or ethane could have been imagined due to a relatively low gravity and due to a remarkably dense atmosphere. Reality is sometimes much beyond what analysts had anticipated or imagined.
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The image above reveals a portion of a radar swath obtained from the Cassini orbiter during the T-104 flyby performed on August 21, 2014. Each side of that portion is approximately 100 kilometers long. The file name of the original view is BIFQI77N241_D261_T104S05_V03.jpg. One can notice a relatively dark and uniform area representing a portion of a pool of hydrocarbons as well as a bright and irregular area representing a portion of the coastline. Several small bright patches can be identified inside the pool. They may correspond to islands, icebergs or glaciers. Are those features stable over time ? Credit for the original image: PDS Image Atlas. Montage credit: Marc Lafferre, 2024. |
- To get further information on that news, go to: https://www.utsa.edu/today/2024/01/story/professor-discovery-new-reality-on-saturns-moon.html and https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023GL106156 .