Outer Satellites Discovered Around Jupiter in 2002




University of Hawaii astronomers announce the discovery of 11 satellites of Jupiter. These satellites, when added to the eleven discovered in 2000 by the Hawaii team, bring the total of known Jupiter satellites to 39. Jupiter now has more known satellites than any other planet.


Discovery of the satellites

The satellites were discovered during mid-December of 2001 by a team led by Scott S. Sheppard and David Jewitt and including Jan Kleyna. They used the Canada-France-Hawaii (3.6 meter) telescope with one of the largest digital imaging cameras in the world, the "12K" camera, to obtain sensitive images of a wide area around Jupiter. The digital images were processed using high speed computers and then searched with an efficient computer algorithm. The program looked for objects with movements characteristic of objects that are near Jupiter. When an object was detected by the program visual confirmation was made by eye. If the candidate looked good it was observed during succeeding months at the University of Hawaii 2.2 meter telescope to confirm their orbits. Orbits for the satellites were fitted by both Robert Jacobson at the NASA Jet Propulsion Laboratory and Brian Marsden at the Minor Planet Center. The satellites were formally announced by the International Astronomical Union on Circular No. 7900 on May 16, 2002.

Figure 1: A movie of the discovery images of the Jupiter satellite S/2001 J3. Click on the above image to see the individual images and learn more about them.


Sizes of the satellites

All the discovered satellites are between about 2 and 4 kilometers in diameter. These estimates are based on the albedo or amount of Sun light reflected from the satellites suface as being about 4% of what they receive. The sizes could be slightly bigger or smaller depending on their surface properties and albedos which have yet to be measured for the satellites.

Orbital data on the Jupiter Satellites


Orbits of the satellites

The 11 satellites are all irregular satellites of Jupiter. That is they have large orbits, eccentricities and inclinations. In particular these 11 new satellites also orbit in retrograde orbits, or opposite the rotation of the planet. They all have similar semi-major axes (about 300 Jupiter radii) and inclinations (about 150 degrees). These characteristics are the same as the other 14 known retrograde satellites of Jupiter. Jupiter appears to have 5 distinct groups of satellites: small inner regulars, Galileans (both shown in Figure 3), prograde irregulars 1, prograde irregulars 2, and retrograde irregulars (shown in Figure 4).

FIGURE 5: A schematic of Jupiter showing the irregular satellite orbits. Click on the above figure to see an enlarged version.


To learn more about the satellites of Jupiter visit The Jupiter Satellite Page.

Scott S. Sheppard