For nearly twenty years, the scientific community has considered Titan, Saturn’s largest moonas one of the most promising places for the search for extraterrestrial life: an “ocean world”, moving tens of kilometers under a thick layer of ice. Apparently, however, this image could be wrong. A new research published on Nature and presented at the annual meeting of the American Geophysical Union is calling this certainty into question, suggesting that Titan could be more solid and less “aquatic” than we thought.
The new study on Titan
The study Titan’s strong tidal dissipation precludes a subsurface oceanled by Flavio Petricca, a planetary scientist at NASA’s Jet Propulsion Laboratory (JPL), says that although Titan may have hosted a global ocean in the past, today that world would be almost completely frozen.
This discovery not only rewrites the geological history of Saturn’s moon, but opens a heated debate among experts who have analyzed the data of the historic Cassini mission. It was precisely thanks to the data from this mission that, at the end of the 2000s, they had proven the existence of this underground ocean. These were mainly radio experiments: by measuring the tiny variations in the speed of the probe, caused by the moon’s gravity, the researchers observed that Titan underwent significant elastic deformations, such as tides induced by the attraction of Saturn. This rising and lowering of the surface could only be explained by the presence of a liquid layer.
Yet the conclusion, today, seems to be wrong. Petricca and his team found some inconsistencies: “If Titan had an ocean, the moon shouldn’t emit so much heat [circa 4 terawatt, ndr]: Most of the frictional heat generated by its bending would instead go to keeping the ocean warm and liquid.”
But not only that. Again according to what is reported in the new study, the presence of an internal ocean should have acted as a sort of “brake”, making Titan’s orbit circular over the millennia. Orbit that still remains elliptical.
The new model
So what’s on Saturn’s largest moon? The proposed new model describes a world with about 500 kilometers of ice resting directly on a 2,000 kilometer rocky core. Petricca explains that this scheme is the only one capable of explaining the previous and latest observations: “This is the first time that everything is explained simultaneously by a single model. This is the most convincing evidence we have.”
The research team hypothesizes that the ocean is solidified in geologically recent times (tens or hundreds of millions of years ago) and that water is still present in the form of “melt zones” or isolated chambers within the ice. A “blotchy” configuration that could be potentially more interesting for the search for extraterrestrial life. Ashley Schoenfeld, a planetary geologist at JPL, explains it: “The oceans are very large and very dilute, and are not necessarily a great way to concentrate materials important for life. A world full of small molten chambers is an even more convincing argument in support of the astrobiological potential of Titan”.
The new model appears solid, but there are those who have doubts. The researchers’ challenge now is only one: understanding what physical mechanism would prevent these molten zones from merging back into a global ocean, absorbing frictional heat. It will have to wait until 2034when NASA’s Dragonfly mission lands a helicopter drone on Titan.
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