Titan ‘escapes’ from Saturn 100 times faster than expected – Space & Astronomy


Titan is on the run: the largest moon of Saturn moves away from its planet by about 11 centimeters per year, with a speed that is 100 times higher than that assumed so far. This was discovered by an international team of researchers, including four from the University of Bologna, thanks to the data of the Cassini-Huygens mission, born from the collaboration between NASA, the European Space Agency (ESA) and the Italian Space Agency (ASI). The study, published in Nature Astronomy, modifies the hypotheses made to date on the evolution of the Saturn system, confirming a new theory that could also be applied to other moons and planets.

Calculating exactly the speed with which Saturn’s satellites move away would solve the mystery of their age, going back to the moment they were formed. In the past 50 years, the orbital migration of the moons has been estimated based on the classical theory of tides, because just as the Moon produces tides on Earth, Titan also does the same on Saturn, since however the planet rotates around its axis faster than Titan rotates around it, the tidal peak on Saturn is not precisely directed towards its satellite, but precedes it. Due to this misalignment, Titan receives a gravitational thrust that takes him away from Saturn. According to tide theory, the outermost moons like Titan should move more slowly than those closest to the planet. Now the hypothesis is questioned by Cassini, who between ten and 2016 made ten flyovers of Titan.

The radio signals sent during these close passages, compared with the photographic images taken by the probe and the observations made with terrestrial telescopes, show that Titan moves away from Saturn a hundred times faster than predicted by the classical theory of tides, about 11 centimeters every year . This surprising result could be explained by a new theory (that of “resonance locking”) conceived four years ago by Jim Fuller, a researcher at the California Institute of Technology and co-author of the research. The theory predicts a rapid orbital migration of the moons of the gas planets caused by particular resonances between the oscillations of the internal structure of the planet and the orbital motion of the moons. These resonances can capture the moons during the evolution of the planet and therefore make them migrate faster than with the classic tide mechanism. Having obtained this important confirmation on Titan, the theory of “resonance locking” could now be applied to study the evolution of other planetary systems, for example that of Jupiter, and also of extrasolar planetary systems and binary star systems.


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