January 29, 2025: Experimental Heating Of Complex Organics Demonstrates That Internal Activity Plays A Role In The Stability Of The Atmosphere Of Titan
A new study entitled "Experimental heating of complex organic matter at Titan's interior conditions supports contributions to atmospheric N2 and CH4", published in Geochimica et Cosmochimica Acta in the volume 390 of February 1, 2025 and proposed by a team of researchers involving Doctor Kelly Miller of the Southwest Research Institute reveals the potential role of the internal chemistry of Titan in the stability of its atmosphere. The largest moon of the Gas Giant Saturn is clearly a unique world in the Solar System due to its remarkable atmosphere that is deep and thick and that may resemble the atmosphere of the Early Earth. The atmosphere of Titan is in fact dominated by molecular nitrogen like the atmosphere of the Blue Planet. Nitrogen represents about 95 percent of the composition of the atmosphere of the giant moon which represents a higher fraction than that of nitrogen in our own atmosphere (around 78 percent). Oxygen that is widespread in our own atmosphere, representing about 21 percent of the composition, is absent or almost absent in the atmosphere of Titan. The atmosphere of that exotic world unveils a relatively high concentration of methane (around 5 percent of the composition at sea level).
How can we explain that Titan contains a significant atmosphere whereas most of the other moons in the Solar System are devoid of any atmosphere ? The largest moon in the Solar System that is to say Ganymede is devoid of any significant atmosphere for instance. Yet, that moon is relatively big and it evolves in a relatively cold environment around the Gas Giant Jupiter. A world like Mercury is also devoid of any significant atmosphere. Yet, Mercury is bigger than our moon, The Moon, but it evolves in a very warm environment around the Sun so that volatiles can more easily escape from the gravity of the planet. The presence of any atmosphere is in fact closely related to the factor of gravity and to the factor of environmental temperature. In principle, there must be the right combination of gravity and environmental temperature for the presence and the stability of any atmosphere. Worlds like Triton and Pluto contain a thin atmosphere. That configuration is probably related to the right combination of gravity and environmental temperature. Their gravity is particularly weak compared to that of the Earth but they evolve in an extremely harsh environment where the ambient temperature is much lower than that of the Earth.
Nature can surprise us and Titan has been a surprise as soon as the discovery of its remarkable atmosphere. The Huygens probe had plunged into that mysterious atmosphere on January 14, 2005 recording a significant amount of data regarding its composition in particular. At sea level on Titan, the atmospheric pressure is about 1.5 times higher than that of the Earth at sea level. One has to keep in mind that the air is particularly dense at sea level on Titan. The Titanian air at sea level is around 4 times denser than the air we have on Earth at sea level. That's surprising for such a small world. Some researchers have imagined or calculated that we could almost take off on that type of environment if we could run fast enough with some equipment ! It is quite hard to imagine what we could feel on that world in terms of physics or dynamics but we could have a better idea if we scuba dive because water is much denser than the air at sea level and because the liquid significantly slows down the fall due to its high density. In principle, it is much easier for a rotorcraft to evolve at a relatively low altitude on Titan than on the Earth or Mars. On Mars for instance, the air at sea level is extremely thin so that the blades of the rotorcraft or helicopter must turn much faster than on Earth for it to take off and fly.
The presence of a relatively high concentration of methane in the atmosphere of Saturn's largest moon is surprising because methane is supposed to disappear over geological time scales due to the action of ultraviolet light from the Sun in particular. The researchers of the study advance that methane is supposed to completely vanish in about 30 million years due to that action of solar radiations. The elimination of methane could have led to a freezing process of the resulting atmosphere onto the surface of that world. The current configuration of the atmosphere of the Orange Moon implies that there may be internal sources to the methane found in that gas blanket. That's a strong hypothesis that planetologists have put forward for a long time. Kelly Miller had already published, in 2019, in the Astrophysical Journal, a research work on a theoretical model regarding the way the atmosphere of Titan had developed and on the way that atmosphere is replenished over time. The study suggests that significant amounts of highly complex organic materials are heated up in the rocky interior of that world engendering nitrogen as well as carbon-made volatiles such as methane.
The gases produced in extreme conditions in the interior of the moon tend to go up and to seep out at the surface. A relatively significant fraction of the atmosphere may in fact have some internal origins with internal compounds or elements regularly fueling that atmosphere. That hypothesis is in line with the experiments of the planetologists in which organic materials were heated to temperatures of 250 to 500 degrees Celsius at pressures up to 10 kilobars to simulate the potential environment in the interior of that world where gases can be engendered. The experiments revealed the creation of relatively large amounts of molecules containing carbon like carbon dioxide and methane. The quantities of molecules produced in the experiments are sufficient to validate the hypothesis of the team of researchers. One can imagine that the external crust of Titan is rich in water ice or even in carbon dioxide ice due to the extremely low environmental temperature. The Huygens probe had recorded a relatively strong release of methane at the time of the impact on the moon at a relatively low latitude in the Shangri-La / Adiri region. That demonstrates that the landscape can be relatively varied in terms of composition.
What is the source of the molecular nitrogen found in the atmosphere of Titan ? Ammonia ice (NH3) can be found beneath the crust of that world and engender nitrogen as well as hydrogen or molecular hydrogen. Organics and hydrocarbons found beneath the crust can also engender other molecules or particles such as methane, acetylene, ethane, carbon dioxide or hydrogen cyanide. The experiments led by the team of planetologists suggest that the concentration of CH4 and CO2 produced depends on multiple factors such as the factor of temperature that appears crucial and such as the dielectric constant of water and carbonyl abundance in the area of the interior where those molecules or particles can be engendered. The production of CH4 can be strong enough if temperatures are greater than 250 degrees Celsius. The composition of the atmosphere of Titan represents the typical composition of the atmosphere of the icy worlds found in the Outer Solar System containing a thin or thick atmosphere. The thin atmosphere of Triton is also dominated by molecular nitrogen. The thin atmosphere of Pluto is dominated by molecular nitrogen as well and contains a relatively significant fraction of methane.
Triton and Pluto represent relatively small worlds which are big enough in their environment to retain an atmosphere in the long run or periodically. Are there internal sources to their thin atmosphere ? The flyby of Neptune performed by the Voyager 2 probe in 1989 had revealed that Triton contains active geysers or black smokers that may play a role in the development or the stability of the atmosphere. The flyby of Pluto performed by the New Horizons spacecraft in 2015 had revealed an active world containing relatively significant amounts of nitrogen ice and carbon monoxide ice. Landscape features that appear to represent impressive cryovolcanoes had also been identified. Those presumed cryovolcanoes demonstrate the potential role of internal sources in the development or the stability of the atmosphere. The analysis of the atmosphere of those worlds can help us better understand the origin, the nature and the evolution of Titan's atmosphere. That atmosphere appears completely opaque from outer space due to a global complex haze that represents a soup of molecules and particles interacting with solar radiations and in particular ultraviolet light from the Sun.
The Cassini-Huygens mission has allowed us to determine that Titan's atmosphere is particularly dynamic and that the landscape of that world is far from being uniform with landscape features or atmospheric phenomena that are comparable to landscape features or atmospheric phenomena on Earth. Like on Earth, there are lakes, seas and rivers on Titan. However, those lakes, seas or rivers are dominated by liquid methane or liquid ethane on Titan. Water can only be present in its solid form on the surface of Titan due to the extremely harsh environmental temperatures. The dynamics of liquid methane or liquid ethane on Titan is comparable to the dynamics of liquid water on Earth. There are evaporation processes, condensation processes and precipitation processes on Titan. The Cassini spacecraft had clearly revealed the presence of clouds, storms or cyclones on Titan. Strong rainfall events can take shape from time to time in the low or middle latitudes for instance. There is a meteorology involving methane or ethane on Titan and regional factors as well as seasonal factors must play a key role. The atmosphere, the climate and the meteorology of Titan can tell us a lot regarding the origin and the evolution of our own atmosphere.
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The image in the upper part of the table represents a view of Titan acquired on February 20, 2013 from the Cassini orbiter on the basis of the CL1 filter and of the CB3 filter. The image whose file name is N00202903.jpg had not been validated or calibrated at the time of the observation and a validated or calibrated version of the original image had to be archived with the Planetary Data System proposed by NASA. One can clearly notice the presence of a polar vortex in the view of the disk. That vortex appeared above the south polar region of the giant moon. The view in the lower part of the table represents a colorized version of the original image. Credit for the original image: NASA/JPL-Caltech/Space Science Institute. Credit for the colorization process of the original image: Marc Lafferre, 2025. |
- To get further information on that news, go to: https://www.swri.org/newsroom/press-releases/swri-designed-experiments-corroborate-theory-about-how-titan-maintains-its-atmosphere and https://www.sciencedirect.com/science/article/pii/S001670372400677X?via%3Dihub.