June 26, 2019 : A Team Of Researchers Led By Morgan Cable Reveals The Potential Presence Of Bathtub Rings Of Acetylene And Butane Around The Pools Of Titan

A new research work led by Morgan L. Cable and involving Tuan Hoang Vu and Robert P. Hodyss from the Jet Propulsion Laboratory of NASA in Pasadena (California) as well as Helen Elizabeth Maynard-Casely from the Australian Nuclear Science and Technology Organization, Kirrawee, NSW in Australia reveals, on the basis of observations and laboratory experiments, the potential presence of rings of acetylene and benzene around the lakes or seas of Saturn's largest moon Titan. The study entitled  The acetylene-butane co-crystal: A potentially abundant molecular mineral on Titan  was presented at the 2019 Astrobiology Science Conference at the Hyatt Regency Bellevue, Evergreen Ballroom in Washington on June 24, 2019. Titan is a really strange world rich in various types of hydrocarbons and organics and planetologists try to imagine or to anticipate the exotic chemistry involving organics that can take shape on the surface or in the atmosphere of the Opaque Moon. Thanks to laboratory experiments, the team of Morgan Cable was in a position to identify exotic minerals or exotic crystals that may exist on the giant moon of the Gas Giant Saturn.

The laboratory experiments were supposed to simulate the exotic environment of Titan where the air is dominated by molecular nitrogen and methane and where various types of organics or hydrocarbons can form. In fact, the composition of Titan's atmosphere is close to the composition of our atmosphere since both atmospheres are dominated by molecular nitrogen. However, oxygen which is relatively abundant in the atmosphere of the Earth is absent or completely absent in the Titanian atmosphere. The environmental temperature of the Orange Moon is extremely low with a surface temperature around minus 180 degrees Celsius, minus 292 degrees Fahrenheit or 93 Kelvin at  sea level . Therefore, water can only appear in its solid form on the surface of the second largest moon in the Solar System. The gravity on Titan is lower than that of the Moon but, curiously, the atmospheric pressure on the surface of Titan is much higher than that of the Earth at sea level. On January 14, 2005, the Huygens probe had recorded an atmospheric pressure of 1,467 hPa on Titan's surface. A parallel can be drawn between the meteorological cycle of the Earth which is based on water and the meteorological cycle of Titan which is based on methane.

During the Cassini mission, we have been in a position to clearly identify, on the basis of infrared, near-infrared or radar data, lakes, seas and rivers in the high latitudes of Titan. The level or the size of the pools of hydrocarbons which may be dominated by methane and ethane may vary during the Titanian year due to seasonal factors. Precipitation processes, condensation processes or evaporation processes can influence the level or the size of the pools like on Earth. The images acquired in the infrared or near-infrared spectrum have revealed what may be deposits of organic evaporite minerals around some lakes or seas found in the high latitudes of the northern hemisphere. Those landscape features may be closely related to evaporation processes of the pools of methane or ethane. The harsh environment of Titan allows methane, ethane and propane to appear in their liquid form on the surface. The pools of hydrocarbons may also contain dissolved nitrogen which can produce bubbles from time to time. Molecules like acetylene and butane can appear in their solid form on the surface of the Opaque Moon. On our planet, molecules like methane, ethane, butane or acetylene represent gases and the molecules of butane and acetylene are used for welding or camp stove fuel for instance.

The new study shows that acetylene and butane can combine to form exotic crystals in the particular environment of the Orange Moon. Morgan Cable advanced that the new mineral studied by her group of researchers may engender the bathtub rings that are thought to take shape around the pools of hydrocarbons. The phenomenon may be encountered around seas or lakes like Ontario Lacus in the high latitudes of the southern hemisphere and Kraken Mare, Ligeia Mare or Punga Mare in the high latitudes of the northern hemisphere. The Equatorial or Tropical areas of the giant moon appear to be dry today. The dark areas of the low or mid-latitudes unveil linear and parallel dunes extending over long distances. However, some ancient lakes or seas may have been identified in those latitudes. Previous analyses based on images and various data obtained from the Cassini orbiter during its relatively long mission in the Saturn System have revealed, at a relatively low latitude, potential lakes unveiling signs of evaporated compounds left behind. Those features can be compared to rings in a bathtub.

The team of Morgan Cable tried to simulate the harsh environment of Titan with the right ingredients that is to say nitrogen, methane, ethane and other hydrocarbons or carbon-containing molecules. The scientists mobilized a custom-built cryostat in order to simulate the particularly harsh environment of Titan where the mean temperatures are much lower than the mean temperatures of the Antarctic for instance. They incorporated liquid nitrogen into the apparatus. Then, the planetologists warmed the chamber a little bit so that nitrogen can appear in its gaseous form. Let's recall that the Titanian atmosphere is dominated by molecular nitrogen and that it contains a haze or a smog rich in organics and hydrocarbons. The next step was to incorporate methane, ethane and other molecules containing carbon atoms into the chamber since the atmosphere of Titan is relatively rich in methane and since it contains various types of hydrocarbons or organics in its haze. Ultraviolet light from the Sun is known to play a key role in the chemistry of Titan's haze.

During the laboratory simulation, the researchers observed that the first molecules to be engendered from the soup or the mixture of hydrocarbons were benzene crystals. Benzene represents a molecule of hydrocarbon whose chemical formula is C6H6 and which is an ingredient of gasoline. Benzene represents a snowflake-shaped molecule composed of a hexagonal ring of carbon atoms connected to hydrogen atoms. The scientists were surprised to see that the molecules had rearranged themselves and that ethane molecules had been captured inside those molecules so that a co-crystal had been produced. Then, the planetologists identified the acetylene and butane co-crystal, a compound that appears to be more abundant than benzene crystals on Saturn's largest moon on the basis of our current knowledge regarding the composition of the Opaque Moon as Morgan Cable pointed out. In the extremely harsh environment of the Orange Moon, the researchers believe that the acetylene-butane co-crystals might produce rings around the pools due to the combined process of evaporation of hydrocarbons like methane or ethane and of accumulation of minerals near the lakes or seas.

A parallel can be drawn between that exotic process and the process of salt formation which results in the development of crusts on the shores of Terrestrial lakes or seas. Morgan Cable and her team believe in that type of process for the lakes or seas on that enigmatic moon of the Ringed Planet. Researchers think that a particularly complex chemistry occurs on Titan thanks to the action of solar radiations and in particular UV light from the Sun and thanks to the action of surface liquids likely dominated by methane and ethane. Morgan Cable and her team will have to wait until a probe, a drone or a lander can explore the shorelines of the Opaque Moon in order to check whether the giant moon unveils the presumed or hypothetical bathtub rings of co-crystals as well as other potential hydrocarbon crystals that we may not have anticipated as Morgan Cable argued. She pointed out :  We don't know yet if we have these bathtub rings.  She added :  It's hard to see through Titan's hazy atmosphere.  The infrared or near-infrared data obtained from the Cassini orbiter have allowed us to discern surface features on the Opaque Moon but the landscape features are often hard to interpret. That's why we have to be cautious in our interpretations.

Many questions regarding the pools of hydrocarbons of Titan must be answered or solved. The Earth and Titan are the only worlds in the Solar System containing stable pools of liquid. Thanks to Titan, we know that one can encounter exotic seas or lakes beyond the Earth. Liquid water is only present on the surface of our planet among the multitude of worlds in the Solar System, from Mercury to Venus, Mars or the Dwarf Planet Pluto. The radar data obtained from the Cassini orbiter have clearly shown that there are seas, lakes and rivers in the high latitudes of the giant moon. Many researchers believe that those pools or rivers are related to seasonal factors and are dominated by methane and ethane with concentrations of both hydrocarbons which can vary geographically or seasonally. Planetologists are wondering what kind of exotic chemistry can take shape in those lakes, seas and rivers. Can a prebiotic chemistry develop in those pools of liquid ? The presumed bathtub rings of hydrocarbons can bring us key information regarding the dynamics and the nature of the lakes or seas on Saturn's largest moon.

The image above represents a false-color mosaic of Titan which clearly reveals the land of lakes and seas in the high latitudes of Saturn's largest moon Titan. The view was generated on the basis of infrared data acquired from the Visual and Infrared Mapping Spectrometer (VIMS) of the Cassini orbiter during its mission in the Saturn System. The orange areas may contain compounds related to evaporation processes. A parallel can be drawn between those areas and salt flats on our planet but the nature of the compounds on the Titanian shorelines is likely completely different from that on the Terrestrial shorelines. Image credit: NASA/JPL-Caltech/University of Arizona/University of Idaho.

- To get further information on that news, go to: https://news.agu.org/press-release/bathtub-rings-around-titans-lakes-might-be-made-of-alien-crystals.



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