New model suggests Titan lakes are explosion craters

James Marshall
Сентября 11, 2019

Titan is the only planetary body in the solar system other than Earth known to have stable liquid on its surface. However, we're not talking about water but about hydrocarbon lakes, filled with methane and ethane. Titan has about 650 hydrocarbon lakes in its polar regions.

That is based on specialists at NASA, who've urged a substitute for the long-held idea the lakes have been fashioned by liquid methane dissolving the rock under.

Scientists studying Titan think that the frigid moon's liquid methane could have dissolved the ice and organic compounds in the bedrock, and that those reservoirs could have filled with liquid hydrocarbons.

The smaller lakes near Titan's north pole have steep sides with tall rims that reach high into the moon's sky, radar imagery by NASA's Cassini spacecraft has shown. If true, this would mean that there are at least two mechanisms for forming Titanian lakes. But for other lakes-smaller ones only tens of miles across-it doesn't fit.

According to an worldwide team of scientists led by Giuseppe Mitri of G. d'Annunzio University in Italy, that may be true for the larger lakes, but the radar profiles collected by Cassini in 2017 of the smaller lakes that have very steep rims that soar well above sea level suggest that instead of being formed by methane dissolving down, they were formed by methane exploding up. Now a new theory suggests that some of these bodies of liquid may have literally exploded into existence.

False-color mosaic of Titan's northern lakes, made from infrared data collected by NASA's Cassini spacecraft.

Researchers described their new model Monday in the journal Nature Geoscience.

And the raised rims on these lakes have always been a puzzle, according to Ralph Lorenz, a veteran planetary scientist at Johns Hopkins University's Applied Physics Laboratory.

"The rim goes up, and the karst process works in the opposite way", lead author Giuseppe Mitri, of Italy's G. d'Annunzio University, said in a statement. "We were not finding any explanations that fit with a karstic lake basin". In actuality, the morphology was extra per an explosion crater, the place the rim is fashioned by the ejected materials from the crater inside. "It's totally a different process", Giuseppe Mitri, who led the worldwide team behind the study, said in the press release.

What Could've Caused the Explosions?

"[It] is evidence that Titan has experienced at least one episode of climate change from a colder period in the past", he says.

Using radar data from Cassini, scientists have built computer simulations that show how explosions of warming nitrogen within Titan's crust could have formed such basins.

'In addition to Mars, outer planet moons like Enceladus, Europa and even Titan at the moment are prime contenders for all times elsewhere, ' he added.

In the colder periods, nitrogen dominated the atmosphere, raining down and cycling through the icy crust to collect in pools just below the surface, said Cassini scientist and study co-author Jonathan Lunine of Cornell University in Ithaca, New York.

Then when the methane was restored, it would've acted as a greenhouse gas, warming the moon again. These models propose that small pockets of liquid nitrogen available in Titan's crust had warmed, thereby turning into an explosive gas which blew out the craters that were later filled with liquified methane.

The multitude of small lakes have rims that tower hundreds of feet above sea level. Localised warming would have been enough to trigger the liquid nitrogen to vapourise and blow out a crater.

Linda Spilker, Cassini Project Scientist said in a press release by NASA that, "As scientists continue to mine the treasure trove of Cassini data, we'll keep putting more and more pieces of the puzzle together. Over the next decades, we will come to understand the Saturn system better and better".

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