Before NASA's Cassini mission ended its study of Saturn in 2017, it also flew by Saturn's moon, Titan. The data provided by the Hyugens probe, which was part of the mission, suggested that Titan was the perfect candidate for further exploration.
And now, that data has helped scientists put together the first global geological map of the intriguing icy moon, according to a new study published Monday in the journal Nature Astronomy.
Larger than both our own moon and the planet Mercury, Titan is unique in our solar system. It is the only moon with clouds and a dense atmosphere of nitrogen and methane, which gives it a fuzzy orange appearance.
That dense atmosphere once obscured a greater understanding of Titan from view. But the Cassini data was able to peel back those layers, which is why it's so valuable.
Data from infrared and radar instruments on Cassini reconstructed and mapped the surface of Titan, showcasing six major geological forms along with their age and distribution, as well as the poles.
Titan also has Earth-like liquid bodies on its surface, but the rivers, lakes and seas are made of liquid ethane and methane, which form clouds and cause liquid gas to rain from the sky. The surface temperature is so cold that the rivers and lakes were carved out by methane, the way rocks and lava helped to form features and channels on Earth.
Titan is also believed to have an internal liquid water ocean, like those on Europa, one of Jupiter's moons, and Enceladus, another of Saturn's moons. A few years ago, NASA announced that Europa and Enceladus' oceans have some or most of the ingredients necessary for life as we know it.
Titan's geology is dependent on latitude. At the equator, young dune fields dominate while lakes can be found at the poles.
But the most prominent feature of Titan is intriguing to scientists: organic plains.
The moon's methane cycle is the driver of its geology -- at the poles, humidity helps methane remain in its liquid state. Around the equator, a more arid climate allows dunes sculpted by wind to remain intact.
"The strong latitudinal dependence of the different units gives us clues about how the methane cycle is operating, though there are still mysteries," said Rosaly Lopes, study author and senior research scientist at NASA's Jet Propulsion Laboratory. "For example, most of the surface is covered by organic materials, particularly plains (65%) and dunes (17%). These are formed, we think, by organic materials falling down from the atmosphere and being moved around by wind. So this tells us that winds have been very important shaping the surface of Titan."
The discovery that much of Titan is covered in organic plains came as a surprise to the researchers.
"People tend to know more about and study the more 'interesting' features on Titan, such as lakes (which cover only 1.5% of the surface)," Lopes said. "The older materials, which we call hummocky, consist mostly of hills and mountains, which we think represent the icy shell or crust poke out here and there. But [they] consist of only 14% of the surface. They have largely been covered over by the organic plains and the dunes."
Earlier this year, NASA announced that the Dragonfly mission will launch in 2026 and explore Titan in 2034.
The ultimate goal is for Dragonfly to visit an impact crater, where they believe that important ingredients for life mixed together when something hit Titan in the past, possibly tens of thousands of years ago.
It may not be like the alien life in science fiction, but in 2017 researchers confirmed the presence of something that may lead to life on Titan, according to a study published in the journal Science Advances.
Vinyl cyanide is a complex organic molecule capable of forming cell membrane-like spheres. While it may sound toxic, this chemical would be right at home on Titan, where significant quantities of it have been detected through data from the Atacama Large Millimeter Array, a group of radio telescopes in Chile.
Dragonfly is about the size of the Mars rover, reaching roughly 10 feet in length. Once Dragonfly lands, it will spend two and a half years flying around Titan. It only has propellers, with skids to land, but no wheels to allow it to roam over the surface.
Dragonfly will also explore Titan's atmosphere, surface properties, subsurface ocean and liquid on the surface.
This new global map can help provide context for anything discovered on Titan by Dragonfly, Lopes said.
"We still have a lot of questions about Titan. To me, the most interesting are the ones connected to habitability," Lopes said. "Dragonfly is a mission that will directly sample the surface and answer many questions about the composition and potential habitability."
Lopes is working on a separate project with the NASA Astrobiology program to understand more about Titan's potential habitability.
"The fact that we have so much organic material on Titan has important implications for life," Lopes said. "The map gives us the global distribution of these organics. We are working on landscape evolution models to understand how the material moves across the surface, and where and how it could penetrate the ice crust -- or penetrated in the past. Organics getting to the ocean, the most likely habitable environment, is key for habitability."