The Science Behind Cassini's Titan Flybys
The enigmatic moon is slowly revealing its secrets one flyby at a time.
Titan is a mysterious world full of hydrocarbon lakes, an orange atmosphere replete with tholins, and a liquid cycle similar to Earth's water cycle. Some scientists think this Saturn moon looks a bit like Earth did before life arose.
Cassini has been orbiting Saturn since 2004 and its time there is rapidly approaching an end. Next year, the spacecraft will be put on a deliberate suicide plunge into the ringed planet. Fortunately it's spent a lot of time getting personal with the atmospheric moon and has done many flybys of Titan so far in 2016. Here are a selection of the flybys -- and scientific findings -- of Titan discussed this year:
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On Aug. 10, Cassini flew past Titan to learn more about the moon's deep structure. During flyby, the spacecraft deployed its radio instrument to try to find a global subsurface ocean, narrow down the shape of Titan and figure out how the icy crust flows. Additionally, Cassini's cosmic dust analyzer attempted to watch nanometer-scale dust interacting with Titan's atmosphere. Scientists are trying to follow up on a phenomenon observed in March 2014 when the instrument saw dust particle impacts drop when Saturn set behind Titan's atmosphere.
Image: An artist's illustration of the interior of Titan, as imagined in 2010. Credit: NASA
On July 25, Cassini went in search of evidence of cryovolcanoes in two regions of Titan: Tui Regio and Hotei Arcus. It had made some flybys of those regions in 2008 and mission planners were looking to see what sorts of changes have occurred in the eight years since then. If these are not cryovolcanic areas, it's possible that they are dried-up lakes.
Image: Artist's impression of Hotei Arcus on Titan. Credit: NASA/JPL
How dense is Titan's atmosphere? While it's been measured many times, on April 4 NASA took another look using Cassini. That's because when they tried to compare atmospheric densities at different latitudes -- using measurements made in different areas at different times -- the results were not correlating with what scientists expected. At the time, they were planning to measure Titan's atmosphere with two instruments at the same latitude, to provide less variability.
Image: Sunlight shines through the edges of Titan's atmosphere in this Cassini image. Credit: NASA/JPL-Caltech
During a Jan. 16 flyby, Cassini's composite infrared spectrometer took a look at the limb (edge of Titan) for both the north and south hemispheres. The idea was to contrast how the atmosphere looks at different seasons during Titan's year. Handily, spring is happening in the northern hemisphere and fall in the southern atmosphere. "Rapid changes in atmospheric circulation are occurring in both hemispheres that have planetary scientists riveted to see what will happen next," NASA wrote at the time.
Image: Radar-imaged lakes seen on the surface of Titan by the Cassini spacecraft. Credit: NASA/JPL-Caltech/ASI/USGS
Cassini data is constantly being analyzed to figure out the conditions on Titan in the past and present. Here are some of the major findings released this year:
- Titan's tallest peak (that we know of) was found. It rises 10,948 feet (3,337 meters) above the surface and is located in some mountainous ridges.
- Based on probing of Ligeia Mare, this sea was found to mostly be made up of methane. The methane supply could come from rainfall, or perhaps ethane (which should be in high abundance in the lake, but is not seen) is being removed via the crust.
- Hydrogen cyanide found on Titan could react with other molecules to create polymers, or long chains of molecules. One possibly polymer called polyimine can use the sun's energy as a spark for life.
- The first liquid-filled channels on Titan were found, as well as huge canyons that go hundreds of feet deep.