Crater walls around Titan may be the result of explosions of liquid nitrogen — New discoveries revealed in data from the Cassini orbiter.
Titan is one of the most unique worlds in our Solar System, with an atmosphere thicker than that on Earth, mighty lakes of hydrocarbons near its poles, and sheer rock faces, some reaching hundreds of feet above the surface of the alien moon.
The lakes of Titan are thought to form as liquid methane dissolves a bedrock of solid organic compounds and ice, forming reservoirs which fill with liquid hydrocarbons. This process is thought to be similar to the chain of events which form karstic lakes within limestone deposits on Earth. On both worlds, these formations are marked by sharp boundaries of surrounding material.
However, the presence of tall cliffs around a fraction of these lakes is difficult to explain using the karstic model. Astronomers studying these cliffs in detail have proposed a new idea for smaller lakes (tens of miles across) which could explain the unusual topography.
“We were not finding any explanation that fit with a karstic lake basin. In reality, the morphology was more consistent with an explosion crater, where the rim is formed by the ejected material from the crater interior. It’s totally a different process, stated Giuseppe Mitri of Italy’s G. d’Annunzio University.
As deposits of liquid nitrogen under the surface of Titan warm, increasing pressure might culminate in explosions. These events could lift material from the surface, forming the cliff walls, researchers propose.
Winnipeg Lacus, near the north pole of Titan, is one crater marked by steep walls which may have been formed by such an event, researchers suggest.
Think of the Oceanfront Property!
Titan is the second-largest moon in the solar system — just two percent smaller than Jupiter’s Ganymede. Larger even than the planet Mercury, it is the only moon known to possess a significant atmosphere — thicker than that found on Earth. This dense atmosphere blocks our view, in visible light, of the surface of this mighty moon.
Titan is the only body in our solar system, other than the Earth, known to be home to seas, lakes, and rivers. In place of water, these bodies are filled with hydrocarbons, including methane and ethane. On Earth, these compounds are usually found as gases, but they act like a liquid in the freezing climate found on Titan.
The atmosphere of Titan in the modern age is composed largely of nitrogen (94 percent), mixed with a small amount of methane. Hundreds of millions of years ago, a different atmosphere — one largely devoid of methane — would have driven temperatures far lower than they are today.
“Lakes of liquid nitrogen may have existed during the epochs of Titan’s past in which methane was photochemically depleted, leaving a nearly pure molecular nitrogen atmosphere and, thus, far colder temperatures,” researchers wrote in Nature Geoscience.
Gaseous methane surrounding Titan acts as a greenhouse gas, keeping that moon warmer than it would be without an atmosphere. Over time, methane is depleted, and replenished, by chemical processes.
This cycle results in warmer and cooler temperatures than we see on that world today. Colder eras were marked by atmospheres filled with nitrogen. This gas collected and fell like rain onto the surface, where some of it collected in wells. Warming periods could build up pressure within these deposits, releasing pressure during eruptions, this new study concludes.
The explosions, researchers surmise, would be similar to interactions between magma and water on our own world. Confirmation of these explosive events would suggest one or more warming events during the geological past on Saturn’s largest moon.
“When all else fails: explosions.”
― Laini Taylor, Strange the Dreamer
“These lakes with steep edges, ramparts and raised rims would be a signpost of periods in Titan’s history when there was liquid nitrogen on the surface and in the crust,” said Cassini scientist Jonathan Lunine of Cornell University.
The Cassini spacecraft, which revealed the data utilized in this study, was accompanied on its journey to Saturn by the Huygens spacecraft, which entered the atmosphere of Titan in 2005 on the first mission ever to explore that mysterious moon.
Soon after its last views of Titan, the Cassini spacecraft was extinguished during a planned suicidal fall into the clouds of Saturn in September 2017. Without this maneuver, the vehicle — and any biological samples that may have hitched a ride on the craft (tardigrades, anyone?) could have posed a hazard to the moons in that system.
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