Astronomers find 12 new moons orbiting Jupiter, including an "oddball"

Federico Mansilla
Julio 17, 2018

It was probably right in the middle of the planets we know so well, Sheppard said.

Credit: Carnegie Institution for Science.

The small moon rotates at the distance of the retrograde moons, but it's traveling in the other direction.

The team is calling one of the new moons an "oddball" because of its unusual orbit. It is also likely Jupiter's smallest known moon, being less than one kilometre [0.6 miles] in diameter'. Most likely to be pieces of a once larger moon that was broken up in orbit, they take almost a year to complete a lap around Jupiter.

But Sheppard suspects these moons could be holdouts, the "last remnants" of early solar system objects.

At less than two miles (3.2km) wide, the moons are all very small, which is why they have only now been identified thanks to the team's modern, sensitive telescopes.

Nine of the new moons have retrograde orbits meaning they orbit in the opposite direction of Jupiter's spin. Nine of the new satellites orbit in a distant swarm of outer moons that are thought to be leftover from a series of collisions that might have involved what were once three larger bodies.

Astronomers looking for stuff in the outer Solar System have received a huge and unexpected surprise - the accidental discovery of 12 previously unknown moons in orbit around Jupiter.

The remaining two satellites others are among a closer, inner group that orbit in the prograde, or same direction. Each takes about two years to circle the planet.

Scientists believe moons like Valetudo and its siblings appeared soon after Jupiter formed.

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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. It crosses the orbits of other moons, and that's where things might get dicey.

A greater number of irregular moons because it tells us about a time during Jupiter's formation when the planet was still growing. "New cameras allow us to cover the whole space around Jupiter in a few images, and this camera is well-shaded", Sheppard said. "Head-on collisions would quickly break apart and grind the objects down to dust".

"If we do find this planet in the next few years, it would be a pretty wonderful discovery for astronomy".

Sheppard's team speculates Valetudo could be a remnant of a collision between one or more moons.

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.

As part of that search, Sheppard was using the 4-meter Víctor Blanco Telescope in Chile in March of previous year and realized that Jupiter was right near the part of the sky he wanted to search. With orbital periods of about one year, they also are thought to be the result of earlier collisions. Sheppard added that his team performed similar moon searches at Uranus and Neptune - but came up empty.

And that raises a question: Does an object less than a mile across deserve to be called a moon? Sheppard believes it could be Jupiter's smallest, and it has an orbit unlike any other moon around the planet.

This was at a time when the Sun was still surrounded by a rotating disc of gas and dust from which the planets were born.

But he said he expects astronomers will discover more tiny moons in the coming decades.

The IAU requires moons of Jupiter to have names related to the Roman god Jupiter. So they were likely formed after they had dissipated.

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