(CN) – Radar data and images from the only spacecraft to ever orbit Saturn revealed small yet surprisingly deep methane-filled liquid lakes perched atop hills on Titan, the gas giant’s largest moon, NASA revealed Monday.
After setting out to explore the sixth planet from the Sun in 1997, NASA’s Cassini spacecraft sent back more than 450,000 stunning images of Saturn, its rings and its moons, including evidence of ocean worlds on Enceladus and Titan.
Cassini disintegrated in the skies above Saturn in September 2017 after its fuel tanks were depleted, ending a remarkable 20-year journey that stretched across billions of miles of our galaxy.
On its final flyby of Saturn’s largest moon in 2017, Cassini gathered the first radar data on the depth and composition of the liquid lakes on Titan – the only planetary body in our solar system other than Earth known to have stable liquid on its surface.
NASA’s study, published Monday in Nature Astronomy, found that the lakes – which are tens of miles wide, far above sea level and more than 300 feet deep – were likely formed when the surrounding bedrock of ice chemically dissolved and collapsed.
On Earth, water lakes formed by the erosion of surrounding limestone bedrock are known as karstic lakes. Karstic lakes exist in Germany, Croatia and the United States.
Cassini scientist and study co-author Jonathan Lunine of Cornell University said in a statement Monday that while Titan’s hydrologic cycle works similarly to Earth’s, the cycle’s behavior in the Northern hemisphere looks different in the Southern hemisphere.
“It is as if you looked down on the Earth’s North Pole and could see that North America had completely different geologic setting for bodies of liquid than Asia does,” Lunine said.
Unlike on Earth – where water evaporates from seas, forming clouds and rain – the temperature is cold enough on Titan for methane and ethane to behave as liquids, raining on, evaporating from and seeping into the ground, leaving reservoirs of liquid stored below, the study said.
The California Institute of Technology’s Marco Mastrogiuseppe, lead author of the study, said the findings help answer a few key questions.
“Every time we make discoveries on Titan, Titan becomes more and more mysterious,” Mastrogiuseppe said in a statement. “We can actually now better understand the hydrology of Titan.”
Scientists have known that Titan’s northern seas are filled with methane – thanks to images taken by Cassini, which arrived in the Saturn system in 2004 – but said that finding the smaller northern lakes filled mostly with methane was a surprise.
Cassini mapped more than 620,000 square miles of liquid lakes and seas on Titan, using a camera that could penetrate the moon’s thick atmospheric haze and a radio instrument that collected information about the terrain and the liquid bodies’ depth and composition.
Lunine said the crucial data for the study were gathered on Cassini’s final close flyby of Titan, on April 22, 2017.
“This was Cassini’s last hurrah at Titan, and it really was a feat,” Lunine said.