March 13, 2024: High-Resolution Spectra Of Titan Suggest The Presence Of C3 In Its Atmosphere In Particular
A new research work entitled "A study of very high resolution visible spectra of Titan: Line characterisation in visible CH4 bands and the search for C3", published in Planetary and Space Science in January 2024 and proposed by a team involving Rafael Rianco-Silva suggests the presence of C3 in the atmosphere of Titan on the basis of high-resolution spectra in visible CH4 bands. The high-resolution visible spectra of Saturn's largest moon were obtained from Earth with VLT-UVES. The planetologists mobilized and analyzed an empirical high resolution list of methane absorption features at a high resolution between 5250 A and 6180 A. A major goal of the study was to identify the presence of C3 in the opaque atmosphere of the giant moon. The presence of C3 in the Titanian atmosphere had been predicted but never detected. The researchers tried to find it at its 4051 A band. The outcome of the team is consistent with the presence of the tricarbon molecule (C3) in the upper atmosphere of the Orange Moon, with a column density of 10^13 cm-2. The research work based on high-resolution visible spectroscopy allows astronomers to deepen their knowledge regarding atmospheres in which CH4 is the main visible molecular absorber. They are in a position to analyze the CH4 optical properties and the chemistry of that soup of molecules or elements.
The complex atmosphere of Titan is likely to tell us a lot regarding the atmosphere of exoplanets containing methane like Uranus or Neptune for instance. The atmosphere of Saturn's largest moon is dominated by molecular nitrogen like the atmosphere of the Earth or like the atmosphere of the Dwarf Planet Pluto as well. To a certain extent, the atmosphere of Titan may look like the atmosphere of the Early Earth. A major difference between the atmosphere of Titan and the atmosphere of the Earth is related to methane. The second most abundant gas in the atmosphere of Titan is methane rather than oxygen which is absent or almost absent in its harsh atmosphere. The atmosphere of the Earth contains around 21 percent of oxygen thanks to our biosphere. The environmental configuration is very different on Titan. The level of energy received from the Sun at the level of Titan is particularly low so that the environmental temperature at the level of the surface is around -179 degrees Celsius, -290 degrees Fahrenheit or 94 Kelvin. That's a configuration in which water can only appear in its solid form on the surface. Oxygen elements will tend to be trapped within the water molecules or in water ice.
The giant moon of Saturn represents a natural laboratory to study the chemistry of hydrocarbons and organics because there is a relatively significant concentration of methane in its atmosphere. Planetologists are particularly interested in the chemistry of the global haze as well as in the chemistry of the upper atmosphere of that world where ultraviolet light from the Sun interacts with the various elements, molecules or radicals to engender new molecules, elements or radicals. The photochemical haze of the upper atmosphere can produce interesting chemicals rich in carbon. The heaviest molecules will tend to go down or to fall due to their weight. The Cassini-Huygens mission in the Saturn System has allowed us to have a much better insight into the complex chemistry of Titan in particular. Molecules like methane, ethane or even propane can be found on the surface in their liquid form thanks to the extremely low environmental temperatures. The Huygens probe had revealed the presence of bright hills containing dark sinuous channels at a low latitude in the southern hemisphere, in the area of the relatively dark Shangri-La and of the relatively bright Adiri.
The dark sinuous channels identified from the Huygens module during its atmospheric descent on January 14, 2005 may represent drainage channels closely related to major meteorological events like heavy rainstorm events, storms or "monsoon events". In fact, the methane we have clearly identified in the deep and thick atmosphere can produce rainfall events. A parallel can be drawn between the meteorological cycle of the Earth based on water and the meteorological cycle of Titan based on methane. We still have a lot to learn about the climate or the meteorological cycle of Titan and it will take time because a year on Titan is particularly long. It takes almost 30 Terrestrial years for the Saturn System to perform a full revolution around the Sun. Therefore, a year on Titan represents almost 30 Earth years. And a Titanian season is also particularly long. A season on Titan represents around 7 Earth years. The obliquity of Titan is higher than that of the Earth so that seasonal changes can be significant. Furthermore, the distance between Titan and the Sun can significantly vary during a Titanian year. Thus, the meteorology can significantly evolve during a Titanian year.
The various infrared or near-infrared images as well as the radar views of the giant moon obtained from the Cassini orbiter during its long mission in the Saturn System from 2004 to 2017 have clearly revealed the complexity of the geology, of the meteorology and of the chemistry of that mysterious world. The radar views acquired from the Cassini spacecraft have clearly shown that the surface is far from being uniform. The configuration on Titan is very different from that of the other worlds evolving aroung the Gas Giant Saturn. Impact craters are scarce thanks to a relatively active meteorology in particular. That meteorology implies the action of winds that can engender the formation of dunes as well as the action of liquid methane or liquid ethane that can form clouds and fall as rain. The haze can produce relatively complex molecules containing carbon atoms that will tend to fall to the surface. A dark or orange mud related to the haze can be found on the surface. Planetologists have determined that a type of dark or orange mud or sludge known as tholin can be found on the surface of Terrestrial worlds or icy worlds in the Outer Solar System.
How can we explain that the low latitudes of the Orange Moon are relatively dry compared to the high latitudes which contain lakes, seas or rivers of liquid methane or liquid ethane ? That's a major question the researchers must answer. The radar views of Titan clearly show that the high latitudes of the northern hemisphere contain a relatively significant concentration of lakes, seas and rivers. Is the dichotomy between the north polar region and the south polar region, in terms of humidity, related to seasonal factors ? Is it related to internal factors, to properties of the external crust or to orbital factors ? There may be internal sources to the methane we observe in the atmosphere. Is there a layer of liquid methane or liquid ethane beneath the external crust in the high latitudes of the northern hemisphere ? Is there a network of subsurface lakes and rivers of liquid methane or liquid ethane beneath the external crust of the northern hemisphere ? That would explain that surprising contrast between the north polar region and the south polar region. The size and the level of the lakes, seas and rivers may be higher during the winter season in the northern hemisphere than during the summer season in the area.
Liquid methane and liquid ethane are likely to act as solvents for the development of complex molecules involving hydrocarbons and organics. Can amino acids, proteins, sugars or lipids form in that type of harsh environment where hydrocarbons and organics are widespread ? Thanks to spectroscopy, we have already identified relatively complex molecules like benzene (C6H6). Can the chemistry of Titan's atmosphere lead to a prebiotic chemistry ? Can liquid methane or liquid ethane engender an exotic lifeform ? That hypothesis can't be ruled out even if a methane-based life or an ethane-based life would probably have a very slow metabolism due to the limited amount of energy available in the environment. Our biosphere is mainly composed of liquid water and mobilizes carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur elements. Any lifeform in the environment of Titan would likely be based on liquid methane and could mobilize elements like carbon, hydrogen, oxygen and nitrogen. A multitude of chemical combinations between those elements can be envisaged in the atmosphere of the giant moon of the Ringed Planet Saturn.
The research work involving Rafael Rianco-Silva who is a scientist of the Institute of Astrophysics and Space Sciences and of the Faculty of Sciences at the University of Lisbon in Portugal raises our level of understanding of the chemistry of an atmosphere where molecular nitrogen and methane are relatively abundant. A better understanding of the chemistry of the atmosphere of Titan can help us produce better models of that type of atmosphere and we can anticipate the type of chemistry one could encounter in the atmosphere of exoplanets containing methane. The exploration of the Solar System has allowed us to determine that Gas Giants, Terrestrial worlds or icy worlds found in the Outer Solar System contain relatively significant concentrations of methane in their atmosphere. That configuration can help us extrapolate the type of atmosphere one could find in the relatively cold areas of other star systems. The high-resolution spectra studied by the team of researchers have allowed us to identify 97 new methane absorption lines in visible light and bring a new light regarding the chemistry of the atmosphere of worlds where methane (CH4) and molecular nitrogen (N2) dominate the composition.
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The image in the upper part of the table represents a raw view of Titan acquired on December 12, 2006 from the Cassini orbiter. The view whose file name is W00020588.jpg was obtained on the basis of the CB3 filter and on the basis of the CL2 filter. The image 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. Surface features can be discerned in the disk. The moon appears completely opaque from outer space due to the presence of a complex haze rich in hydrocarbons and organics. The image 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 view: Marc Lafferre, 2024. |
- To get further information on that news, go to: https://ui.adsabs.harvard.edu/abs/2024P%26SS..24005836R/abstract and https://divulgacao.iastro.pt/pt/2024/03/07/tita-testes-vida-fora-sistema-solar/.