Is Titan Baking its Own Atmosphere? Origin of Mysterious Gases Revealed

Titan, the largest moon of Saturn, is the only satellite in the solar system known to have a thick atmosphere. First studied in detail by the Voyager 1 spacecraft in 1980, the origin of Titan’s atmosphere has puzzled astronomers for decades. But, new research may shed some light on this engaging mystery.

A recent study from the Southwest Research Institute (SwRI) suggests conditions on Titan may bake organic material found in the interior of the world, giving rise to an atmosphere even denser than that found on Earth. Like our own atmosphere, the gases surrounding Titan are mostly nitrogen.

“Titan is a very interesting moon because it has this very thick atmosphere, which makes it unique among moons in our solar system. It is also the only body in the solar system, other than Earth, that has large quantities of liquid on the surface. Titan, however, has liquid hydrocarbons instead of water. A lot of organic chemistry is no doubt happening on Titan, so it’s an undeniable source of curiosity,” said Kelly Miller, research scientist in SwRI’s Space Science and Engineering Division.

Titan Orbiting Saturn
Titan seen orbiting Saturn in a photograph from the Cassini-Huygens mission. Credit: NASA/JPL-Caltech/Space Science Institute

One previous theory postulated that comets placed ammonia (composed of nitrogen and hydrogen) on the surface of Titan. There, chemical processes would break down the ammonia, releasing nitrogen. However, this theory neglects the effects of complex organic materials, which we now know to be common in comets. Investigation of the comet 67P/Churyumov-Gerasimenko by the Rosetta spacecraft revealed 25 percent of the mass of that body was organic materials.

Another odd feature of Titan’s atmosphere is that roughly five percent of it is methane. This gas would rapidly react with other gases, and fall to the ground as organic material. So, that begs the question of how methane in the atmosphere of Titan is replenished.

This new study from SwRI suggests that comets and other small bodies may have delivered vast amounts of organic material to the warmer interior of Titan. There, physical conditions are slowly cooking the material, releasing methane and nitrogen to the atmosphere.

An artist’s concept of the interior structure of Titan, based on data from Cassini. Credit: A. D. Fortes/UCL/STFC

Organic materials do not necessarily develop into life – the term merely refers to complex carbon-rich molecules. But, their presence on Titan makes that world one of the more promising places in the Solar System to search for extraterrestrial life. Space agencies, including NASA, are currently developing plans to explore this giant moon, utilizing drones, gliders, and submarines.

Titan Infrared
Using infrared cameras, it is possible to show surface details beneath the hazy atmosphere of Titan, including seas of sand at the equator, and liquid hydrocarbon seas near the poles. Credit: NASA/JPL-Caltech/University of Arizona

“Titan’s atmosphere also contains an array of more complex organic molecules, including vinyl cyanide… Under the right conditions, like those found on the surface of Titan, vinyl cyanide may naturally coalesce into microscopic spheres resembling cell membranes,” the National Radio Astronomy Observatory announced in July 2017.

Titan is roughly three-quarters the size of Mars, making it the second-largest satellite in the Solar System. Only Ganymede, orbiting Jupiter, is larger. In 1997, NASA launched the Cassini-Huygens mission to Saturn, which arrived at the ringed planet in June 2004. On January 14, 2005, the Huygens probe became the first spacecraft to ever plunge through the atmosphere of Titan.

Analysis of the geothermal and chemical properties of materials in the atmosphere of Titan was published in The Astrophysical Journal.

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