Moon Number 60 for Saturn
The Cassini imaging team announced today the discovery of Saturn’s 60th known natural satellite (going along with the one man-made satellite). This little fellow, provisionally known as S/2007. That’s up from 18 known moons when Cassini was launched in October 1997. The moon is about 2 km in diameter and orbits between Mimas and Enceladus (and between the tiny moons Methone and Pallene discovered earlier in Cassini images). That is fairly close to the rings and raises anew the question of the lifetime of such small moons. The problem is that interplanetary meteoroids (small comets in this part of the solar system) would have a fairly easy time blasting such a small moon to smithereens. Based on estimates of the flux of such comets near Saturn, such moons would not be expected to survive longer than a tiny fraction of the age of the solar system. So, where are these small moons coming from? Or, are our estimates for the (so far unseen) small comets way too high? This moon is in a resonance with Mimas, making it likely that tidal forces caused its orbit to migrate to its present location from somewhere else. Perhaps this is a chunk off the old block, where the old block is one of the more massive nearby moons. If it is part of the debris of a disrupted moon, then we face the unsatisfying proposition of having to assume that we arrived on the scene at Saturn just in time to see these final few fragments. The more we see, the more questions we have.