S/2003 J 20 - Definition and Overview

S/2003 J 20 is a natural satellite of Jupiter. It was discovered by a team of astronomers from the University of Hawaii led by Scott S. Sheppard, et al. in 2003. It orbits Jupiter at a distance of roughly 17,100,000 km. S/2003 J 20 is about 3 kilometers in diameter.

Like Themisto, this moon seems to be the lone member of a unique class, which makes it particularly interesting. The orbital inclination of satellites such as this one is limited by the Kozai effect, discovered by Yoshihide Kozai in 1962. This effect induces a periodic exchange between the inclination and eccentricity of the orbit; if the inclination is large enough, the eccentricity can in turn grow so large that the perizene of the satellite would be in the immediate vicinity of the galilean moons (Io, Europa, Ganymede and Callisto). The satellite would eventually collide with one of these, or a close encounter would eject it altogether from the jovian system.