The Cassini mission ended last September and researchers have now finally completed the map of Saturn’s biggest moon, Titan. There are a lot of interesting new pieces of information in the map but perhaps the most tantalizing is that Titan has a global sea level like Earth.
The research is published in two separate Geophysical Review Letters papers, one focusing on the sea levels and the other describing the detailed map of the moon. The map combines all the Titan typography data available from multiple sources, such as high-resolution images, to produce an interpolated analysis of what the full surface of the moon is likely to look like.
Titan is the only other object in the Solar System that has stable liquid on its surface, although instead of being water it's hydrocarbons; mostly liquid methane and ethane. The Cassini probe was able to measure the sea level to a staggering precision and realized that it was consistent around the moon.
“We’re measuring the elevation of a liquid surface on another body 10 astronomical units away from the sun to an accuracy of roughly 40 centimeters. Because we have such amazing accuracy we were able to see that between these two seas the elevation varied smoothly about 11 meters, relative to the center of mass of Titan, consistent with the expected change in the gravitational potential," Professor Alex Hayes, from Cornell University and lead author of the sea level paper, explained in a statement.
"We are measuring Titan’s geoid. This is the shape that the surface would take under the influence of gravity and rotation alone, which is the same shape that dominates Earth’s oceans.”
Having a global sea level has a very important consequence. It implies that liquid hydrocarbons flow under the surface of Titan, just like water flows through porous rocks in aquifers here on Earth. The team considered lakes, ancient lakes, and watersheds across the surface, and the data seems to be in agreement with their hypothesis.
“We don’t see any empty lakes that are below the local filled lakes because, if they did go below that level, they would be filled themselves,” added Hayes. “This suggests that there’s flow in the subsurface and that they are communicating with each other. It’s also telling us that there is liquid hydrocarbon stored in the subsurface of Titan.”
The study doesn’t just answer questions, though, it also creates a new mystery. Most of Titan’s lakes are located in sharp-edge depressions with ridges hundreds of meters high. The peculiar shapes were described by the team as looking like they were created by cookie cutters. Understanding their formation is key to having a clear picture of the methane cycle on the moon.
Only 9 percent of the whole moon has been mapped in high-resolution, while 25 to 30 percent was imaged in lower resolution. The topography for the rest of Titan was interpolated with state-of-the-art algorithms. Armed with this the researchers were able to discover two locations near the equator that could be old lakes or cryovolcanic flows, and a few new mountains, although none taller than 700 meters (2,300 feet).
Cassini is unfortunately not there anymore to collect more data so, for now, researchers will have to use lab simulations and what has been observed so far to work it all out. Although thanks to the confirmation of hydrothermal activity inside fellow moon Enceladus, we might be going back to Saturn, sooner rather than later.