Astronomers discover 12 more moons of Jupiter

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Our solar system's oldest and biggest planet, Jupiter, has many moons. And astronomers have just announced the discovery of a dozen more.

On Tuesday, the International Astronomical Union’s Minor Planet Center published the orbits for 12 newfound Jovian moons — bringing Jupiter's total to 79 moons, said Scott Sheppard, a scientist at the Carnegie Institution for Science in D.C.

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Most moons, including Earth's, have prograde orbits. Two of the newly discovered moons, the ones closest to Jupiter, have prograde orbits, too.

The other nine moons, grouped in clusters of three, have retrograde orbits. Those moons were probably once part of much larger moons that splintered into smaller objects, Sheppard said. The astronomers are currently running computer simulations to determine how the ancient moons fragmented.

Valetudo is something of an oddball. It has a prograde orbit at a distance where the rest of Jupiter's moons have retrograde orbits. What's more, those orbits intersect. The stage is set, in other words, for possible moon-moon collisions.

The astronomers do not know the composition of the dozen newly identified moons. They could be rock, ice or a mixture. “The only thing that we know at the moment are the orbits and the approximate size,” Williams said. “We know nothing, really, more than that.”