lunar image of the month

may: new moons

Keeping track of the number of moons in the solar system has become quite a challenge lately. During 2000 a record 22 new satellites were reported. For a while, following discoveries in 1997 and 1999, Uranus had the largest family - 21 moons. Now that has been overtaken by Saturn, the current leader with no fewer than 30, and Jupiter, close second with 28.

The newly discovered moons are invariably small, with diameters in the region of 4-30km, and have irregular orbits (highly elliptical, tilted out of the plane of the ecliptic and even retrograde) so they are probably captured asteroids. It will take many more measurements to establish the precise orbits of the new satellites before the International Astronomical Union (IAU) will officially recognise their status and allow them to be given proper names.

This image shows the provisionally-named S/2000 S 1 (meaning first satellite of Saturn reported in 2000) and was taken on 7th August 2000 from the European Southern Observatory in Chile.

Image: B. Gladman et al., Observatoire de la Cote d'Azur), European Southern Observatory.