Abstract Titan, Saturn’s largest satellite, is one of the most intriguing moons in our Solar System, in particular because of its dense and extended nitrogen-based and organic-laden atmosphere. Other unique features include a methanological cycle similar to the Earth’s hydrological one, surface features similar to terrestrial ones, and a probable under-surface liquid water ocean. Besides the dinitrogen main component, the gaseous content includes methane and hydrogen, which, through photochemistry and photolysis, produce a host of trace gases such as hydrocarbons and nitriles. This very advanced organic chemistry creates layers of orange-brown haze surrounding the satellite. The chemical compounds diffuse downward in the form of aerosols and condensates and are finally deposited on the surface. There is very little oxygen in the atmosphere, mainly in the form of H2O, CO, and CO2. The atmospheric chemical and thermal structure varies significantly with seasons, much like on Earth, albeit on much longer time scales. Extensive analysis of Titan data from ground, Earth-orbiting observatories, and space missions, like those returned by the 13-year operating Cassini-Huygens spacecraft, reveals a complex system with strong interactions among the atmosphere, the surface, and the interior. The processes operating in the atmosphere are informative of what occurs on Earth and give hints as to the origin and evolution of our outer Solar System.
Titan is the only moon or planet other than Earth where we have found evidence of bodies of surface liquids. The 1980 Voyager flyby of Titan determined that the surface density of its atmosphere is four times greater than that on Earth. The atmospheric pressure on this moon is 1.6 bars, higher than that on any other moon and, remarkably, even higher than that of the terrestrial planets Mars and Earth. The atmospheric composition is primarily nitrogen, an important way in which Titan’s atmosphere resembles Earth’s. Also detected in Titan’s atmosphere were carbon monoxide (CO), hydrocarbons (compounds of hydrogen and carbon) such as methane (CH4), ethane (C2H6), and propane (C3H8), and nitrogen compounds such as hydrogen cyanide (HCN), cyanogen (C2N2), and cyanoacetylene (HC3N). Their presence indicates an active chemistry in which sunlight interacts with atmospheric nitrogen and methane to create a rich mix of organic molecules. There are also multiple layers of hydrocarbon haze and clouds in the atmosphere, as illustrated in Figure 12.12.
We study the interaction of atomic and molecular hydrogen with a surface of tholin, a man-made polymer considered to be an analogue of aerosol particles present in Titan's atmosphere, using thermal programmed desorption at low temperatures below 30 K. The results are fitted and analyzed using a fine-grained rate equation model that describes the diffusion, reaction and desorption processes. We obtain the energy barriers for diffusion and desorption of atomic and molecular hydrogen. These barriers are found to be in the range of 30 to 60 meV, indicating that atom/molecule-surface interactions in this temperature range are dominated by weak adsorption forces. The implications of these results for the understanding of the atmospheric chemistry of Titan are discussed.
The atmosphere of Titan is the dense layer of gases surrounding Titan, the largest moon of Saturn. Titan is the only natural satellite of a planet in the
The atmosphere of Titan is the dense layer of gases surrounding Titan, the largest moon of Saturn. Titan is the only natural satellite of a planet in the Solar System with an atmosphere that is denser than the atmosphere of Earth and is one of two moons with an atmosphere significant enough to drive weather (the other being the atmosphere of Triton). Titan's lower atmosphere is primarily composed
The atmosphere of Titan is the dense layer of gases surrounding Titan, the largest moon of Saturn. Titan is the only natural satellite of a planet in the Solar System with an atmosphere that is denser than the atmosphere of Earth and is one of two moons with an atmosphere significant enough to drive weather (the other being the atmosphere of Triton). Titan's lower atmosphere is primarily composed of nitrogen (94.2%), methane (5.65%), and hydrogen (0.099%). There are trace amounts of other hydrocarbons, such as ethane, diacetylene, methylacetylene, acetylene, propane, PAHs and of other gases, such as cyanoacetylene, hydrogen cyanide, carbon dioxide, carbon monoxide, cyanogen, acetonitrile, argon and helium. The isotopic study of nitrogen isotopes ratio also suggests acetonitrile may be present in quantities exceeding hydrogen cyanide and cyanoacetylene. The surface pressure is about 50% higher than on Earth at 1.5 bars (147 kPa). This is higher than the pressure at the triple point of methane, which allows there to be liquid methane on the surface in addition to the gaseous methane in the atmosphere. The orange color as seen from space is produced by other more complex chemicals in small quantities, possibly tholins, tar-like organic precipitates.
Evidence that Titan's atmosphere contains over a thousand times more methane than carbon monoxide would appear to rule out significant contributions from cometary impacts, because comets are composed of more carbon monoxide than methane. That Titan might have accreted an atmosphere from the early Saturnian nebula at the time of formation also seems unlikely; in such a case, it ought to have atmospheric abundances similar to the solar nebula, including hydrogen and…
Everything we examined (4)
This check searched the claim as stated. It did not run a separate search for evidence against it.