S u m m a r y :
Saturn’s moon Titan has features that bear resemble to those found on Earth. These new findings, published in the Geophysical Review Letters, come from the updated Cassini data set that provides a more detailed outlook of the moon’s landscape.
Cassini spacecraft was sent to orbit Saturn with the aim of collecting data concerning the planet system, with special focus on the largest moon, Titan. The mission is now complete, and scientists are reviewing all the new information. Recently, two new papers have been published, documenting a global topographic map of Titan as well as the implications concluded from its analysis; the studies were performed by astronomers from Cornell University.
The first study, entitled “Titan’s Topography and Shape at the End of the Cassini Mission”, focuses on the map. The latter was made over a course of a year, says first author Paul Corlies; it is the result of the compilation of all the data on Titan topography from various sources. Only around 9% of Titan’s topography has been captured in high resolution; around 30% observed in lower resolution; the rest, mapped with an interpolation algorithm, and a global minimisation process meant to reduce errors.
The final map show many new features of Titan’s. The mountains found on the moon reach no higher than 700 metres. The highs and lows are also represented, allowing the researchers to conclude that two spots situated near to the equator are depressions that might have arisen from ancient seas or cryovolcanic flows. Another interesting finding is that Titan appears to be flatter than initially thought, implying that its crust might be of different thicknesses.
The map is hoped to assist investigators endeavouring to model the shape, climate, and gravity of Titan; it will also be used to test interior models, and to bring a better understanding of its morphological land forms.
The second paper, entitled “Topographic Constraints on the Evolution and Connectivity of Titan’s Lacustrine Basins”, discusses several important observations from the map, the first of which is that the three seas of Titan form a sea level just like the oceans on Earth. This is due to the presence of a flow through the subsurface between the seas or because of the channels between them causing sufficient volumes of liquid to seep through, resulting in the oceans being on the same elevation.
“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. 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,” says senior author Alex Hayes, who is also involved in the first paper.
The second result of the paper confirms a theory that Hayes mentions in another paper: that the lakes on Titan are connected through the subsurface. Upon measuring the lake elevations (both dried up lakes, and liquid-filled ones), the Hayes and his team have found that the lakes are at hundreds of metres above sea level; within a watershed, the dry lakes’ floors are at higher elevations than the nearby filled lakes.
“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. This suggests that there’s flow in the subsurface and that they are communicating with each other,” said Hayes. “It’s also telling us that there is liquid hydrocarbon stored on the subsurface of Titan.”
Another resemblance with the Earth is the presence of sharp-edged depressions beneath the lakes that “look like you took a cookie cutter and cut out holes in Titan’s surface”. The lakes have high ridges all around them, some of which are hundreds of metres high. They appear to be formed in the same way as karst found on Earth in regions like the Florida Everglades; karst constitutes the landscape beneath limestone, creating ridges, narrow openings, towers, among others. Furthermore, just like the karst on Earth, the Titan lakes are topographically closed, bearing no channel that point inwards or outwards. But, it is to be noted that Earth karst has no sharp edges.