In its final flyby of Saturn's largest moon in 2017, NASA's Cbadini spacecraft collected radar data revealing that the small liquid lakes in the northern hemisphere of Titan are surprisingly deep, positioned at the top of the hills and filled of methane.
The new findings, published on April 15 in Nature Astronomy, are the first confirmation of how deep some of Titan's lakes (more than 300 feet, or 100 meters) and their composition are. They provide new information on how liquid methane rains, evaporates and filters into Titan, the only planetary body in our solar system other than Earth that is known to have stable liquid on its surface.
Scientists have known that Titan's hydrological cycle works in a similar way to Earth's, with a big difference. Instead of water evaporating from the seas, forming clouds and rain, Titan does it all with methane and ethane. We tend to think of these hydrocarbons as a gas on Earth, unless they are pressurized in a tank. But Titan is so cold that they behave like liquids, like gas at room temperature on our planet.
Scientists have known that the much larger north seas are filled with methane, but discovering the smaller northern lakes filled mainly with methane came as a surprise. Previously, Cbadini data measured Ontario Lacus, the only important lake in the southern hemisphere of Titan. There they found an approximately equal mixture of methane and ethane. Ethane is slightly heavier than methane, with more carbon and hydrogen atoms in its composition.
"Every time we make discoveries on Titan, Titan becomes more and more mysterious," said lead author Marco Mastrogiuseppe, a Cbadini radar scientist at Caltech in Pasadena, California. "But these new measurements help answer some key questions, we can now better understand Titan's hydrology."
Adding to the rarities of Titan, with its Earth-like features carved by exotic materials, is the fact that the hydrology on one side of the northern hemisphere is completely different from the other side, said Cbadini co-author and scientist Jonathan Lunine. from Cornell University in Ithaca, New York.
"It's as if you were observing the north pole of the Earth and you could see that North America had a completely different geological configuration for the liquid bodies than Asia," said Lunine.
On the eastern side of Titan, there are large seas with little elevation, canyons and islands. On the western side: small lakes. And the new measurements show the lakes perched on large hills and plateaus. New radar measurements confirm previous findings that lakes are well above sea level, but evoke a new image of landforms, such as tables or specks, that adhere hundreds of feet above the surrounding landscape, with lakes deep liquids at the top.
The fact that these western lakes are small (only tens of kilometers wide) but very deep also tells scientists something new about their geology: it is the best evidence yet that they probably formed when the surrounding ice sheet and organic solids dissolved chemically collapsed On Earth, similar lakes of water are known as karst lakes. Occurring in areas such as Germany, Croatia and the United States, they are formed when water dissolves limestone.
Along with the investigation of deep lakes, a second article in Nature Astronomy helps unravel more of the mystery of Titan's hydrological cycle. The researchers used the Cbadini data to reveal what they call transient lakes. Different sets of observations, from radar and infrared data, seem to show that fluid levels have changed significantly.
The best explanation is that there was a seasonal change in surface fluids, said lead author Shannon MacKenzie, a planetary scientist at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland. "One possibility is that these transient features could have been shallower bodies of liquid that evaporated and infiltrated into the subsoil throughout the season," he said.
These results and the findings of Nature Astronomy's article on Titan's deep lakes support the idea that hydrocarbon rain feeds lakes, which can then evaporate into the atmosphere or drain into the subsoil, leaving liquid deposits stored below.
Cbadini, which arrived in the Saturn system in 2004 and completed its mission in 2017 by deliberately immersing itself in Saturn's atmosphere, mapped more than 620,000 square miles (1.6 million square kilometers) of lakes and liquid seas in the surface of Titan. He did the work with the radar instrument, which emitted radio waves and collected a return signal (or echo) that provided information about the terrain and the composition and depth of the liquid bodies, along with two imaging systems that could penetrate the thick atmosphere of the moon. haze.
Crucial data for the new investigation was gathered on Titini's last Titini closing flight on April 22, 2017. It was the mission's last look at the smallest lakes on the moon, and the team took full advantage of it. . Collecting echoes from the surfaces of small lakes while Cbadini with zipper on Titan was a unique challenge.
"This was Cbadini's last hurray on Titan, and it really was a feat," Lunine said.
The Cbadini-Huygens mission is a cooperative project of NASA, the ESA (European Space Agency) and the Italian Space Agency. NASA's Jet Propulsion Laboratory, a division of Caltech in Pasadena, California, manages the mission for NASA's Science Mission Directorate in Washington. JPL designed, developed and badembled the Cbadini orbiter. The radar instrument was built by JPL and the Italian Space Agency, working with team members from the United States and several European countries.
You can find more information about Cbadini here: https://solarsystem.nasa.gov/cbadini