December 9, 2019 : A New Laboratory Experiment Proposed By Kendra Farnsworth Reveals A Rapid Development Of Bubbles In A Mixture Of Methane And Ethane Strengthening The Hypothesis Of Bubbles In The Famous  Magic Islands  Of Titan

A new study entitled  Nitrogen Exsolution and Bubble Formation in Titan's Lakes , recently published in the journal Geophysical Research Letters and proposed by a team of researchers from the University of Arkansas, reveals the rapid development of bubbles in a mixture of methane, ethane and nitrogen in a laboratory experiment strengthening the hypothesis according to which bubbles may develop in the famous Magic Islands of Titan. Kendra Farnsworth who is the first author of the research work and who is a doctoral candidate in the Arkansas Center for Space and Planetary Sciences tried to reproduce the atmospheric conditions of Saturn's largest moon in one of the center's five planetary simulation chambers. The environment of the Opaque Moon appears to be rich in molecular nitrogen and in methane. During the Cassini-Huygens mission in the Saturn System, we have been in a position to clearly identify lakes, seas or rivers in the high latitudes of the giant moon. The composition of the pools of liquids can vary depending on the area, on the latitude or on the season. Methane, ethane or propane can appear in their liquid form on the surface of Titan.

Kendra Farnsworth who performs maintenance on the Titan Chamber for the Arkansas Center for Space and Planetary Sciences was in a position to determine that, in a harsh environment resembling the environment of Titan, a combination of methane, ethane and nitrogen generates rapid bubble formation. The formation and the development of bubbles had already been hypothesized to explain the phenomenon of the Magic Islands. The Magic Islands represent transient bright patches inside the major lakes or seas found in the high latitudes of the northern hemisphere in some radar views obtained from the Radar Mapper of the Cassini spacecraft during its long mission in the Saturn System. The Cassini orbiter had performed multiple flybys of Titan collecting a huge amount of data with its various instruments. Planetologists have had the opportunity to compare several radar views of the same pools, lakes or seas in order to understand their dynamics or their nature. Close to the coastline of Ligeia Mare, inside the pool which is relatively dark and quite uniform in radar views, large bright patches had taken shape. Then, those bright patches had evolved and dissipated or disappeared.

The phenomenon of the Magic Island clearly represents one of the biggest mysteries in the field of planetary exploration. Several hypotheses have been advanced to explain the sudden formation or development of the bright patches inside the lake or sea. Were the Magic Islands real islands ? Does the Magic Island correspond to a type of iceberg ? Does the Magic Island correspond to an area of relatively strong waves ? Does the Magic Island correspond to an exotic type of bloom of tiny organisms ? Or does it correspond to a field of bubbles related to cryovolcanism or chemical interactions ? Numerous hypotheses can be advanced to explain that captivating phenomenon. In the extreme environment of the Opaque Moon where the ambient temperature close to the surface is around minus 179 degrees Celsius, minus 290 degrees Fahrenheit or 94 Kelvin, water can only appear in its solid form on the surface but there are liquids on Titan's surface. The Orange Moon seems to have various types of lakes and seas because several hydrocarbons can appear in their liquid form on the surface of that enigmatic moon. Planetologists are particularly interested in the potential interactions between methane and ethane.

Specialists of Titan believe that the three main compounds of Titan's lakes, seas or rivers are methane, ethane and nitrogen. The environmental temperature of Titan is too high or not low enough to allow the presence of liquid nitrogen on the surface but nitrogen can appear within the lakes or seas. Planetologists believe that there is dissolved nitrogen within the pools dominated by hydrocarbons on Saturn's largest moon. That's why methane, ethane and nitrogen are generally mobilized in the laboratory experiments. The interactions are quite complex since they depend on the concentration of each molecule and on the environmental temperature. A limited variation in the environmental temperature can have a significant impact on the activity of the lake or sea. Nitrogen can generate bubbles within the lakes or seas like carbon dioxide within a drink. The lighter molecules tend to go up whereas the heavier molecules tend to go down due to gravity. Kendra Farnsworth and her collaborators advance that the bubbles taking shape within the pools can be strong enough to influence the geology of the moon. They pointed out :  Bubbles may be common in Titan's lakes and may be significant in the geologic processing of Titan's river outlets, such as the development of deltas in Ontario Lacus. 

Titan is really a fascinating world because it looks like the Earth to a certain extent. There are cloud formations, cyclones or vortices, rainfall events and probably snowfall events. The Titanian lakes or seas composed of molecules which represent gases on Earth undergo the influence of seasonal factors during the particularly long year at the level of Saturn and its moons. Methane plays the same role in the Titanian environment as water in our own environment. Water is widespread in the form of ice on Titan. And there may even be a subsurface ocean dominated by liquid water beneath the external crust of the second largest moon in the Solar System. Specialists of Titan are particularly interested in the interactions between the atmosphere, the soil, the crust and the hypothetical subsurface ocean. The humid areas tend to be found in the high latitudes or in the polar regions of the giant moon and we want to know why. The radar images and the infrared or near-infrared views acquired from the Cassini orbiter during its orbital dance around the Ringed Planet have clearly shown that the lakes or the seas are mainly found in the high latitudes of the northern hemisphere.

The first pool of liquids identified on Titan was Ontario Lacus, a lake or sea located in the high latitudes of the southern hemisphere. Researchers had clearly spotted a dark patch in infrared or near-infrared views taken from the Cassini spacecraft. Later, we obtained radar data of that lake or sea which looks like a foot or a kidney. Ontario Lacus was first observed during the Summer season in the southern hemisphere. The southern hemisphere turns out to be less humid than the northern hemisphere. Planetologists believe that the dichotomy in the distribution of lakes, seas and rivers between the southern hemisphere and the northern hemisphere is related to seasonal factors and the particular physical or orbital configuration. The orbit of the Saturn System around the Sun is far from being circular. Like the orbit of the Earth around the Sun, the orbit of Saturn and its numerous moons is elliptical. The Earth evolves at its closest point from the Sun during the Summer season in the southern hemisphere whereas it evolves at its farthest point from the Sun during the Summer season in the northern hemisphere. Obviously, the environmental temperature depends on the obliquity of the planetary body but it also depends on the variation in the distance between the planetary body and the Sun during the orbital dance.

The amount of solar energy received by Saturn's largest moon during its orbital dance around the Sun can significantly vary during the Saturn year which is very long since it lasts almost 30 Earth years. A Titanian season lasts approximately 7 Earth years. The Cassini spacecraft has obtained data for 3 different Titanian seasons from 2004 to 2017. We know that seasonal factors play a significant role in the dynamics or the chemistry of the lakes, seas or rivers of Titan but the interactions between the pools of liquids and the crust or the subsurface layers represent a big question mark. Are there internal sources for the methane present in the rivers, in the lakes, in the seas or in the atmosphere ? Is there a subsurface layer dominated by liquid methane ? We know that the haze of Titan's atmosphere can produce various molecules such as organics or hydrocarbons. We know that the heavier molecules will tend to fall toward the surface and can generate a type of mud known as tholin. The dunes found in the low or mid-latitudes of the giant moon may have been engendered by the organic haze. The ultraviolet light from the Sun plays a key role in the chemistry of that exotic haze.

The chemistry of organics and hydrocarbons on Titan may tell us a lot regarding the chemistry of organics on our own planet. The lakes, seas and rivers of the Opaque Moon are likely to accelerate chemical reactions and to engender complex molecules like sugars or even amino acids. That's why the study of the Titanian pools of liquid hydrocarbons appears particularly fundamental. The phenomenon of the Magic Island demonstrates that the lakes or seas found in the high latitudes of the northern hemisphere are not always quiet like a lake at a high altitude in the mountains. Kraken Mare or Ligeia Mare may contain active areas where special chemical reactions take shape. One can imagine the potential phenomena occurring in those exotic pools or one can perform laboratory experiments like the laboratory experiment proposed by Kendra Farnsworth and her team. Nitrogen that dominates the Titanian atmosphere and our own atmosphere can interact with liquid methane and liquid ethane to produce bubbles. However, that's only one hypothesis among other hypotheses which must be considered to explain the phenomenon of the Magic Island. For instance, are there portions of the soil beneath the lake or sea that can go up toward the surface to form icebergs ? Are the lakes or seas sleeping above cryovolcanoes ?

The image above represents a portion of the radar swath obtained from the Cassini spacecraft on May 12, 2007 during the T30 Flyby of Saturn's largest moon. The portion is 100 km wide and 100 km high. A portion of Kraken Mare, the largest pool of liquids on Titan, can be clearly seen. One can notice numerous islands in particular. The phenomenon of the Magic Island may not be related to the presence of a real island. The new research work strengthens the hypothesis of a field of bubbles producing the radar signature of an island. Credit for the original radar view: NASA/JPL/Cassini RADAR Team/Jason Perry. Credit for the montage: Marc Lafferre, 2019.

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