August 27, 2020 : An Ecosystem In Kraken Mare Or Ligeia Mare Explored By A Submarine In The Coming Decades ?
Beyond Earth, in the Solar System, there is another world where pools of stable liquid can be found on the surface. That world is Titan, the largest moon of the Gas Giant Saturn. The radar views as well as the infrared or near-infrared views of the second largest moon in the Solar System have clearly shown that the polar regions of that enigmatic world contain lakes, seas and rivers. Curiously, the pools of liquid are mostly concentrated in the high latitudes. The most humid area of Titan appears in the high latitudes of the northern hemisphere. The south polar region is dominated by Ontario Lacus, a lake or sea whose shape is reminiscent of a foot. The north polar region is dominated by Kraken Mare, Ligeia Mare and Punga Mare. Those lakes or seas represent key targets to explore in the coming decades. Specialists of Titan are eager to explore those attractive areas via probes, boats, drones or submarines. The exact nature of the liquid found in the pools or rivers of Titan remains a mystery today. However, the key molecules of the lakes, seas and rivers of the Opaque Moon must be methane and ethane. The concentration of each molecule within the liquids may be intimately linked to the period of the Titan year or may be intimately linked to the area of the globe.
A presentation upon the concept of a submarine to explore the lakes or seas of Titan was recently performed by Steven Oleson of NASA's Glenn Research Center in Ohio with the Future In-Space Operations working group from the agency. Steven Oleson pointed out that a submarine to explore the seas or lakes of Titan may represent the first step in the exploration of extraterrestrial lakes, seas or oceans. If the mission which involves a submarine to explore the lakes or seas of the Orange Moon is a success, we will be in a position to develop more complex missions to explore the subsurface lakes, seas or oceans of worlds like Europa or Enceladus. Europa and Enceladus contain an icy crust which represents a barrier for the study or the exploration of the presumed subsurface ocean of liquid water hidden beneath that icy crust which may be relatively thick. Several other worlds in the Solar System may also contain subsurface lakes, seas or oceans of liquid water. One can mention Ceres, Ganymede, the largest moon in the Solar System, Triton or Pluto. Titan may also contain a subsurface ocean of liquid water but the lakes, seas or rivers found on the external crust are likely dominated by a mixture of methane and ethane.
Astrobiologists or planetologists are particularly interested in the exploration of Titan's atmosphere, Titan's surface or Titan's pools of liquids because that world is rich in hydrocarbons and organics. The deep and opaque atmosphere of Saturn's largest moon contains an exotic haze where complex carbon-based molecules can take shape and fall toward the surface. Titan's atmosphere generates clouds which can produce rain. Therefore, a parallel can be drawn between the meteorological cycle of Titan dominated by methane and the meteorological cycle of the Earth dominated by water. Are there exotic microorganisms, bacteria or archaea thriving in the atmosphere, on the surface, inside the crust or in the lakes, seas or rivers of the Hazy Moon ? Are there more complex creatures in the pools of liquid hydrocarbons found in the high latitudes ? One can imagine that the biosphere based on liquid methane or liquid ethane would be quite different from the biosphere based on liquid water in terms of chemistry. In the harsh environment of Titan, water can only appear in its solid form on the surface but the molecules of methane, ethane or propane can appear in their liquid form.
Can methane represent a good solvent for the development of any exotic lifeform ? Could a lifeform based on liquid methane reach the same degree of complexity as the lifeform based on liquid water ? Some researchers advance that there may be a subsurface layer dominated by liquid water beneath the external crust of the giant moon. Therefore, potentially, there can be two types of lifeform on the moon or inside the moon. In the pools or rivers of liquid methane or ethane, there may be a lifeform based on liquid hydrocarbons and in the subsurface lakes, seas or oceans dominated by liquid water beneath the external crust, there may be a lifeform based on liquid water. One can advance that the presumed subsurface ocean of liquid water that may be salty like our own oceans may host an ecosystem that may look like the typical ecosystems of the Earth. Any lifeform based on liquid water must be based on molecules like amino acids, DNA, RNA, proteins, lipids or sugars. Any lifeform based on liquid methane or liquid ethane may contain more exotic molecules. What would replace DNA ? What type of complex molecule representing the genome can there be ? Nature can really be surprising regarding the development of any complex chemistry.
Our knowledge of Titan is essentially based on data acquired by the Cassini orbiter and the Huygens lander during the Cassini-Huygens mission in the Saturn System from 2004 to 2017. Unfortunately, the Huygens probe did not land in an area of lakes or seas on January 14, 2005. However, the radar views obtained from the Cassini spacecraft have clearly shown that the lakes, seas and rivers are found in the high latitudes of the giant moon. A new project to send an eight-rotor drone to the environment of Titan is now starting for a launch scheduled in 2026 and for a landing onto the surface of Titan scheduled in 2034. The project is known as Dragonfly. The drone will study, in particular, the land of dunes which may be rich in organics or hydrocarbons. Will it find complex organics or a prebiotic chemistry ? A major goal is obviously to send a probe to study the land of lakes, seas and rivers in the north polar region of Titan. Steven Oleson and his collaborators have obtained two rounds of funding from the NASA Innovative Advanced Concepts (NIAC) program. The two NIAC grants must allow the development of clear concepts or ideas to explore the lakes, seas or rivers of Saturn's largest moon.
Steven Oleson pointed out that the main purpose of the research work was to produce a basic engineering blueprint of a potential submarine to explore the seas or lakes of Titan. The technological challenge to send a submarine to the lakes or seas of that world is far from being easy. One has to anticipate the particularity of the exotic environment of the moon. The gravity of Titan is much lower than that of the Earth. The gravity of the Opaque Moon is even lower than that of our moon. Therefore, the natural downward movement of the submarine is likely to be slower than in the oceans of the Earth. Since the mean density of methane or ethane is lower than that of liquid water on Earth, the submarine would not undergo a strong resistance in its movement. The liquids of the lakes or seas are transparent to radio signals so that the submarine could easily communicate with the orbiter or with the control stations on Earth. Several configurations have been imagined by Steven Oleson and his team. In the configuration in which the submarine directly communicates with the control stations on Earth, the submarine must be big and heavy. The submarine is approximately 20 feet or 6 meters long and its weight on our planet is around 3,300 lbs or 1,500 kilograms.
In the configuration in which there is also an orbiter to transmit data to the submarine or to collect data from the submarine, the submarine is lighter and would be 6.5 feet or 2 meters long with a weight of approximately 1,100 lbs or 500 kilograms. It contains the same instruments as in the first configuration but the communications equipment is lighter. Planetologists and engineers envisage, at least, a chemistry package to analyze the liquid samples, a surface imager, a depth sounder, a weather station and a device to determine the physical properties of the sea or lake. Other instruments can also be added like a device to analyze the samples found at the bottom of the lake or sea or a special imager to acquire images of the bottom of the lake or sea. Another configuration which appears less complex or risky is a configuration in which there is a boat that would release, from time to time, dropsondes to study the environment beneath the surface of the lake or sea. That option may be less fruitful because the analysis of the lake or sea would be quite limited. Clearly, the configuration of the big submarine that directly communicates with the control stations on Earth and the configuration of the smaller submarine that communicates with an orbiter appear to be the most interesting options.
The most interesting configurations may represent Flagship missions like the Cassini-Huygens mission, the Mars rover Curiosity mission or the Mars 2020 rover Perseverance. Several billion dollars must be mobilized but is it too much to study an extraterrestrial lake or sea ? New Frontiers missions can also be selected by NASA. A boat for the lakes or seas of Titan may be envisaged for that class of missions whose cost must be below the limit of 850 million dollars without the cost related to the launching phase and without the cost related to mission operations. The source of energy for the boat, for the submarine or for the orbiter would represent nuclear power because the Saturn System evolves too far away from the Sun so that the level of energy received at that distance from our star is particularly low. Solar panels appear useless in that type of environment. Kraken Mare and Ligeia Mare are clearly key targets to explore. Kraken Mare is the biggest pool of liquids on Titan. It covers approximately 154,000 square miles or 400,000 square kilometers whereas Ligeia Mare covers approximately 50,000 square miles or 130,000 square kilometers. The maximum depth of Ligeia Mare represents 560 feet or 170 meters and Kraken Mare is at least 115 feet or 35 meters deep. The perfect time to explore those pools of liquids will be during the Summer season in the northern hemisphere in the 40's.
The image above reveals a radar portion of the famous sea Kraken Mare and of the famous island Mayda Insula. The view represents a portion of a radar swath obtained from the Cassini orbiter on February 22, 2007 during the T25 Flyby. Kraken Mare represents a captivating environment for any mission to explore the enigmatic environment of the Hazy Moon. The view is about 100 km wide and about 100 km high. Credit for the original radar view: NASA/JPL/Cassini RADAR Team/Jason Perry.
- To get further information on that news, go to: http://fiso.spiritastro.net/telecon/Oleson_7-22-20/ and https://www.space.com/saturn-moon-titan-submarine-concept-mission.html .