Jupiter's moon count reaches 79, including tiny 'oddball'

This illustration shows the newly discovered moons of Jupiter and their orbits

This illustration shows the newly discovered moons of Jupiter and their orbits

On Tuesday, the International Astronomical Union (IAU) announced the discovery of 10 new moons orbiting Jupiter.

Astronomers spotted the moons in spring 2017 while they were searching for Planet X, a possible planet located beyond Pluto and at least as large as Mars.

That brings the number of moons at Jupiter to 79, the most of any planet.

The initial discovery of most of the new moons were made on the Blanco 4-meter telescope at Cerro Tololo Inter-American in Chile and operated by the National Optical Astronomical Observatory of the United States. "By looking at these outer moons", he said, "we can get an insight into what the objects were like that ended up forming the planets we see today". Measuring less than a mile in diameter, it's the smallest of Jupiter's known moons, and Sheppard describes it as an "oddball". "We think they're something in between the rocky asteroids, which are interior to Jupiter, and the icy comets, which are exterior to Neptune", Sheppard says.

This new "oddball" moon is more distant and more inclined than the prograde group of moons and takes about one and a half years to orbit Jupiter.

Jupiter, the largest planet in the solar system, was hardly short of moons before the latest findings. Like the others, they, too, are thought to be fragments of a larger moon that slammed into something else. "It was a long process", said Scott Sheppard, who led the effort at the Carnegie Institution for Science in Washington DC. "What these other objects were has been a mystery".

Our solar system's oldest and biggest planet, Jupiter, has many moons.

Two of them are pretty straightforward. Two of the newly discovered moons were found among these prograde moons, and take a little less than a year to go around in their orbit once.

But the last moon is a weird one.

One moon detected by Sheppard and his colleagues is the smallest Jovian moon ever discovered. The name Valetudo has been proposed for it, after the Roman god Jupiter's great-granddaughter, the goddess of health and hygiene.

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Astronomers suspect that the retrograde moons may be the remains of larger moons that were destroyed in head-on collisions with prograde objects.

"With the discovery of Valetudo, it seems the collisions that broke apart the retrograde moons were between other prograde Jupiter moons, like Valetudo", Sheppard told ScienceAlert.

A moon is defined as any object, regardless of size, that orbits a planet, not the Sun.

The remaining two satellites others are among a closer, inner group that orbit in the prograde, or same direction.

"What's really cool for me here is what they're calling their oddball", Horner told ScienceAlert.

The curious find might shed light on how many of Jupiter's current moons were formed. Since they are still around, now, that means they formed after that gas and dust had been swept away by the solar wind. These moons orbit in a clockwise direction, in the view above.

The team's results are not yet available in a peer-reviewed journal, as Sheppard's team is now running supercomputer simulations to try and figure out how often Valetudo might collide with a retrograde moon.

"A full paper will likely be written after these simulations are done in a few months".

The so-called "oddball" has such a unique orbit that it is at risk of smashing into the other moons - a cosmic collision that could risk wiping the space rocks out.

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