Details of the SATELLITES OF URANUS and NEPTUNE . The radii of all five satellites of Uranus are too small to be measured directly, but values can be calculated from their observed brightness and an assumed albedo. If they are ice-covered, the radii could be as small as 100km (Miranda) to 350km (Titania) whereas extremely dark surfaces give radii as large as 650 to 2000km. The tabulated values are a compromise between these two extremes.

W.Lassell detected Neptune’s larger satellite, Triton, on 10 October 1846, less than a month after the identification of Neptune itself by J.G.Galle. The only other known satellite of Neptune is Nereid, discovered by G.P.Kuiper on 1 May 1949. The two satellites are quite unlike each other. Triton is in retrograde motion in an orbit close to Neptune with no detected eccentricity whereas Nereid is in direct motion in a highly eccentric orbit far from Neptune. This orbit takes Nereid as close as 140 000km to Neptune and as far away as 9 500 000km. From the observed brightnesses, Triton is apparently large and massive and Nereid is the opposite.

Triton’s retrograde motion suggests that it is a captured asteroid whereas its circular orbit suggests that it is a true satellite. This apparent conflict has led to the suggestion that the planet Pluto is an escaped satellite of Neptune, which sent Triton into its peculiar orbit when it escaped. Pluto is not known to have any satellites.

Comments are closed.