October 2, 2020 : A Subsurface Ocean Of Salty Water Relatively Rich In Complex Organics Beneath The External Crust Of Titan ?
The system of Saturn reveals several moons that may contain a subsurface ocean dominated by liquid water. The Ringed Planet gravitationally interacts with its numerous moons and potentially engenders a relatively strong internal activity for Enceladus, Tethys, Dione, Rhea or even Titan. The moons of the Saturn System undergo the gravitational influence of the Gas Giant as well as the gravitational influence of the other moons in orbit around Saturn. Tidal forces are known to play a key role in the remarkable volcanism of Io, one of the major moons of Jupiter, for instance. Enceladus, the bright icy moon of Saturn, unveils geysers in the fractures found in its south polar region. Those regular eruptions or cryovolcanic events may be closely related to the tidal forces generated by Saturn and the other moons. The geysers of the tiny moon imply that there may be a layer or pockets dominated by liquid water beneath the external crust. Most researchers did not expect to observe such a level of internal activity for a tiny moon whose diameter is around 500 km. The geysers of Enceladus were identified during the Cassini-Huygens mission thanks to the Cassini orbiter which had captured many images of the bright moon from 2004 to 2017.
Planetologists have noted that the moons of Saturn are generally remarkably rich in water ice. The surface of the icy moons tends to be heavily cratered. However, the external crust of moons like Enceladus, Tethys, Dione or Rhea may evolve above a layer dominated by liquid water. The study of Saturn and its moons has clearly changed our view of the worlds found in the Outer Solar System. The moons found beyond Mars receive less energy from the Sun than worlds like Venus or the Earth but they can be active in their interior thanks to the tidal forces generated by the Gas Giants or the Dwarf Planets. That's obviously the case for Io and that may also be the case for moons like Europa, Ganymede, Miranda or Triton. The giant moon Titan evolves farther from Saturn than Mimas or Enceladus but researchers believe, on the basis of data acquired from the Cassini spacecraft, that Titan contains a subsurface ocean dominated by salty liquid water. The presumed subsurface ocean may be found at a depth of at least 50 km or 30 miles beneath the ground. The exact nature of the liquid is unknown due to the limited amount of clues. The exact depth of the hypothetical subsurface ocean is also unknown.
Titan is the only moon containing a significant atmosphere among the numerous moons orbiting the second largest Gas Giant in the Solar System. Titan's atmosphere looks like our atmosphere to a certain extent but there are no clouds of water ice or water vapor on Titan. The clouds of Saturn's largest moon are generally dominated by methane or ethane. Those clouds are related to a meteorological cycle involving methane and comparable to the meteorological cycle of the Earth which involves water. Titan is in fact the only extraterrestrial world in the Solar System containing stable lakes, seas or rivers. Methane can condense and form lakes or seas. Evaporation processes can take shape in the lakes, seas or rivers. Like on Earth, clouds can form on Titan thanks to the well-known condensation processes. The exotic clouds of Titan can engender precipitation processes like on Earth as well. In the harsh environment of the Hazy Moon, water can only appear in its solid form on the surface. Stones or pebbles rich in water ice and roughly as hard as the typical rock on Earth can be encountered on the soil of Titan. The Huygens probe had recorded a surface temperature of about minus 179 degrees Celsius, minus 290 degrees Fahrenheit or 94 Kelvin on January 14, 2005.
Our knowledge upon the nature of the presumed subsurface ocean of Saturn's largest moon can become clearer if we identify and study potential cryovolcanoes on that world. The huge amount of data collected from the Cassini orbiter during its long mission in the Saturn System from 2004 to 2017 has allowed us to determine that the landscape of Titan is remarkably diverse but we have not identified clear signs of cryovolcanism. Some bright landscape features composed of sinuous channels may represent potential cryovolcanoes. But they may also represent the outcome of an impact event. If the topographic feature is roughly circular, it can represent a caldera or a cryovolcanic feature but it can also represent an impact crater. The bright, sinuous features can tell us a lot regarding the nature of the crust or even the nature of the presumed internal ocean. If the crust of Titan looks like the crust of most of the other moons of the Ringed Planet, one can advance that Titan's crust may be rich in water ice. A moon like Tethys is clearly rich in water ice for instance. Titan which is much bigger than Tethys appears to be a differentiated world. In other words, several layers composed of different materials can be found inside the giant moon.
Some topographic fractures have already been identified on Titan thanks to the Radar Mapper of the Cassini orbiter. If the fractures of Titan are similar to the fractures encountered in the south polar region of the tiny moon Enceladus, one can envisage the potential presence of geysers spewing methane, ethane, propane or water ice for instance. In the high latitudes of the northern hemisphere or in the north polar region of Titan, a multitude of lakes, seas and rivers has been identified thanks to the Radar Mapper of the Cassini orbiter in particular. Among the pools of liquids found in the high latitudes of the northern hemisphere, some lakes may be found in cryovolcanic depressions. Therefore, is the presence of methane in those lakes related to subsurface pockets of liquid methane or related to a subsurface sea or ocean dominated by liquid methane ? The analysis of the hydrology of Titan appears more complex than previously believed. How can we explain the dichotomy in the distribution of lakes, seas and rivers on Saturn's largest moon ? Is that geographical dichotomy or asymmetry related to meteorological cycles or related to physical or orbital factors ?
Researchers often say that Titan represents a natural prebiotic laboratory. In fact, the atmosphere of the Opaque Moon may look like the atmosphere of the Early Earth. Titan's atmosphere is dominated by molecular nitrogen like our own atmosphere. However, oxygen is absent or almost absent in the atmosphere of the Orange Moon. In fact, the haze of Saturn's largest moon is rich in organics and hydrocarbons. In Titan's upper atmosphere, complex photochemical reactions occur under the influence of ultraviolet light from the Sun in particular. Methane, ethane, acetylene, ethylene or hydrogen cyanide interact in that photochemical soup to form new molecules or particles. Heavier molecules tend to fall toward the surface. Remarkably complex organics or hydrocarbons have already been found in the exotic atmosphere of the giant moon. Can molecules like amino acids, proteins, sugars or lipids take shape in the harsh environment of the Hazy Moon ? Researchers have reported the presence of natural plastics on Titan. Thanks to the Atacama Large Millimeter/submillimeter Array (ALMA) located in Chile, we have been in a position to identify acrylonitrile in Titan's upper atmosphere.
Acrylonitrile which is also known as vinyl cyanide or propenenitrile and whose chemical formula is C2H3CN is likely to form potential cell membranes. In other words, that molecule can favor complex chemical reactions and lead to the development of life. Titan's haze can produce a type of snow that can form dunes on the surface. Planetologists imagine a red or dark sludge or mud composed of hydrocarbons or organics. The radar data obtained from the Cassini orbiter have clearly revealed the presence of linear and parallel dunes extending over long distances in the dark areas of the low or mid-latitudes of the Opaque Moon. Those dunes may be rich in hydrocarbons like benzene. Can they engender more complex molecules like proteins ? The typical lifeform we encounter on Earth can't be envisaged on the surface of Titan because there are no stable pools of liquid water on the surface. A solvent is needed for the formation and for the development of any lifeform. If there is a lifeform evolving on the surface of Titan, it will probably be based on liquid methane or liquid ethane. But chemical reactions will probably be very slow.
Some planetologists or biologists have envisaged the potential presence of two different types of lifeform in the environment of Saturn's largest moon. In the harsh environment where methane can appear in its liquid form, the hypothetical lifeform is likely to be based on liquid methane. Beneath the external crust, in the presumed liquid layer dominated by water or by a mixture of water and ammonia, the lifeform may look like the lifeform of our biosphere. Nobody really knows whether that configuration is possible because we only know living creatures based on liquid water. Our biosphere is extremely dynamic thanks to the relatively large amount of energy received from the Sun. Thus, chemical reactions involving carbon, water or elements like nitrogen, phosphorus or sulfur occur in a very fluid way. In the harsh environment of Titan, the potential chemical reactions may be much more limited and much slower. The drone of the Dragonfly mission is likely to collect key information regarding the secrets of organic chemistry. If we find a water-based life in the presumed subsurface ocean of liquid water above the presumed rocky core, we will probably be in a position to establish a new principle of mother nature.
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The image above reveals bright crescents of Titan and Saturn, two enigmatic worlds of the Solar System. Titan's atmosphere appears completely opaque from outer space due to the haze of hydrocarbons and organics in particular. Titan looks like a Gas Giant from outer space to a certain extent but the giant moon has a solid surface whereas Saturn roughly represents a ball of gas or plasma dominated by hydrogen and helium. The view was obtained in visible green light with the Wide-Angle Camera of the Cassini spacecraft on May 22, 2015. At the time of the observation, the orbiter was evolving 0.3 degrees below the ring plane of the Gas Giant and was moving at a distance of about 1.4 million miles or 2.2 million kilometers from the Ringed Planet. Image credit: NASA/JPL-Caltech/Space Science Institute. |
- To get further information on that news, go to: https://solarsystem.nasa.gov/news/1517/saturn-and-titan-resources/?page=0&per_page=40&order=created_at+desc&search=&tags=Saturn%2CTitan%2CCassini%2CEnceladus&category=324.