In the first images Methone appeared only as a small bright spot and therefore nothing was known about its physical characteristics.
Instead, it was immediately possible to calculate its orbital parameters. In particular, it was discovered that the semi-major axis of its orbit periodically varies by 20 km due to an orbital resonance with Mimas, another Saturnian moon.
The first close-up images, taken by Cassini in 2012, were full of surprises. In fact, Methone was expected to be an irregular satellite full of craters like most of all of Saturn's small moons.
Methone, however, turned out to be a body with a regular shape with an average diameter of just 3 km and with a very smooth surface without craters.
Its appearance could be explained starting from its composition. Cassini data suggests that Methone has a density of just 0.31 g/cm3, one of the lowest values in the entire Solar System. It would therefore seem that such a light structure is able to explain the observed lack of craters.
Credit: NASA, JPL, SSI.
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