Heating of complex organic matter in the presence of water may be an important source of Titan’s abundant atmospheric nitrogen and methane gases, according to new research from Southwest Research Institute and Carnegie Institution for Science.
Titan’s abundant atmospheric nitrogen and methane gases are notable characteristics of the moon that may help constrain its origin and evolution. Image credit: SwRI.
The origin, age, and evolution of the atmosphere of Saturn’s moon Titan, which is roughly 95% nitrogen and 5% methane, has puzzled scientists since it was discovered in 1944.
“While just 40% the diameter of the Earth, Titan has an atmosphere 1.5 times as dense as the Earth’s, even with a lower gravity,” said Dr. Kelly Miller, a researcher at Southwest Research Institute.
“Walking on the surface of Titan would feel a bit like scuba diving.”
“The presence of methane is critical to the existence of Titan’s atmosphere.”
“The methane is removed by reactions caused by sunlight and would disappear in about 30 million years after which the atmosphere would freeze onto the surface.”
“Scientists think an internal source must replenish the methane, or else the atmosphere has a geologically short lifetime.”
In en earlier study, Dr. Miller and colleagues proposed a theoretical model of how the atmosphere may have developed and is replenished over the years.
They theorized that large amounts of highly complex organic materials are heated up in Titan’s rocky interior, releasing nitrogen as well as carbon gases like methane.
The gas then seeps out at the surface, where it forms a thick atmosphere around the moon.
This theory is corroborated by the team’s new experiments that heated organic materials to temperatures of 250 to 500 Celsius at pressures up to 10 kilobars to simulate the interior conditions of Titan.
The experiments produced carbon gases like carbon dioxide and methane in sufficient quantities to help supply Titan’s atmospheric reservoir.
They are largely based on data from NASA’s Cassini-Huygens spacecraft mission, which launched in 1997 and explored the Saturn system from 2004 to 2017.
“Our results indicate both methane and carbon dioxide are formed, with the ratio between the two depending on a multitude of factors, particularly temperature and, to a lesser degree, the dielectric constant of water and carbonyl abundance in the starting material,” the researchers said.
“Sufficient methane is produced to source Titan’s atmospheric reservoir if temperatures are greater than 250 degrees Celsius.”
“Nitrogen is volatilized, primarily in the form of ammonia, in sufficient abundances to source at least 50 % of Titan’s atmospheric nitrogen.”
“The isotopic characteristics of volatilized material relative to the starting organics are consistent with current constraints for the nature of the accreted complex organics and Titan’s evolved atmosphere.”
The team’s findings appear in the journal Geochimica et Cosmochimica Acta.
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K.E. Miller et al. 2025. Experimental heating of complex organic matter at Titan’s interior conditions supports contributions to atmospheric N2 and CH4. Geochimica et Cosmochimica Acta 390: 38-56; doi: 10.1016/j.gca.2024.12.026
