Orbital evolution of the Neptunian moons Hippocamp and Proteus.

The origin and fate of most of the satellites that now orbit Neptune are reasonably well understood, but the orbital evolution of Hippocamp and Proteus is less clear. Proteus is the second largest moon of Neptune, whereas Hippocamp is much smaller. There is increasing evidence that cosmological expansion, as described by the Hubble-Lemaître parameter, occurs in the Solar System. For Hippocamp and Proteus, orbital analysis based on local cosmological expansion shows that neither can be original moons of Neptune since both have only been outside the synchronous (stationary) orbit of Neptune for about 3.3 x 109years (3.3 Gyr). It has previously been suggested that they represent the residues from the break-up of an earlier moon. Furthermore, the orbits of Hippocamp and Proteus coincided at that time. This supports earlier ideas that these two moons arose from the fragmentation of an original body. It may be noted that this epoch, i.e., 3.3 Gyr ago, is consistent with timings in those theories of the "Late Heavy Bombardment," whereby planets and their satellites experienced major asteroid impacts long after the formation of the Solar System. These results are in conflict with the widely held view that cosmological expansion does not operate at the local level. [ABSTRACT FROM AUTHOR]