New moon. Jovian satellite S/2001 J3 is seen moving across the starry background in a timespan of about 1.5 hours.

Move Over, Saturn

Thirty nine and counting--that's the latest tally for the number of satellites orbiting Jupiter. The discovery of 11 tiny moons has restored the planet's title as "King of Satellites," and researchers say the giant is unlikely to ever yield the title again.

These moons are nothing like our own. For starters, they're just 2 to 4 kilometers wide. And according to the discovering team, led by University of Hawaii astronomers Scott Sheppard and David Jewitt, the new moons belong to a large group of far-flung satellites that have eccentric orbits and, unlike most satellites, move in the direction opposite Jupiter's rotation. Most of them take almost 2 years to complete one orbit.

The moons probably formed early in the history of the solar system, when a larger object approached nascent Jupiter and was broken up by tidal forces and friction from the gas that enveloped the forming planet. (If the tiny moons formed from the same gas cloud as Jupiter, scientists reason, they would rotate in the same direction as the planet). The new moons were announced 16 May by the International Astronomical Union (IAU).

There are probably many other such satellites to be discovered, as the team has yet to complete its search of the space around Jupiter. In just the last 18 months, the tally of Jupiter's satellites has more than doubled--in January 2001, the same team discovered another batch of 11 Jovian satellites. (Runner-up Saturn has only 30 satellites. Uranus has 20.) Based on the distribution of satellites found so far, the team expects the final number of satellites to be between 80 and 110.

That could present a problem, says Brian Marsden of the IAU Central Bureau for Astronomical Telegrams. In the past, all of Jupiter's satellites have been named after lovers of Zeus (the Greek name for Jupiter). But with the new satellites awaiting official names, finding appropriate mythological ones will prove to be difficult, says Marsden. "Sooner or later, we will run into trouble here," he notes.

Related sites
The IAU announcement

University of Hawaii Jupiter satellite page

Physical and orbital data for all Jovian satellites