PASADENA, Calif. (CN) – NASA researchers said Monday that explosions of heated nitrogen in the crust of Titan, Saturn’s largest moon, created the deep basins that later became methane-filled lakes, currently the only other sites of stable liquid in our solar system.
On Titan, liquid doesn’t rain down from the heavens and fill bodies of water. Instead, the moon’s frigid climate force gases there – methane and ethane – to act as liquids.
Scientists believe some lakes on Titan likely formed after methane dissolved ice and other solid organic compounds and carved reservoirs into the moon’s surface. On Earth, karstic lakes formed similarly after water dissolved surrounding limestone.
But a team of scientists led by Giuseppe Mitri of Italy’s G. d’Annunzio University believed the karstic model could not explain the origin of smaller lakes on Titan that feature steep rims towering above sea-level.
In a study published Monday in Nature Geosciences, the researchers said that new radar data from the Cassini spacecraft allows them to turn the karstic model “theory upside down.”
Smaller lakes – such as Winnipeg Lacus near Titan’s north pole – likely formed after liquid nitrogen in the moon’s crust warmed and turned into an explosive gas that blew craters into the surface, the researchers say.
Mitri said in a statement that the karstic process is the “opposite” of what forms smaller lakes on Titan.
“We were not finding any explanation that fit with a karstic lake basin,” Mitri said. “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.”
Cassini disintegrated in the skies above Saturn in 2017 after its fuel tanks were depleted, ending a remarkable 20-year journey that stretched across billions of miles of our galaxy.
The Cassini mission – operated by NASA’s Jet Propulsion Laboratory in Pasadena, California – captured data of Titan’s smaller lakes during its final flyby of the moon.
Cassini scientist and study co-author Jonathan Lunine of Cornell University said in the statement that nitrogen likely dominated Titan’s atmosphere in cooler periods over the last billion years and was kept warm by methane in other eras.
“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,” Lunine said. “Even localized warming would have been enough to turn the liquid nitrogen into vapor, cause it to expand quickly and blow out a crater.”