Web Desk (July 18, 2018): Astronomers found a dozen of new moons orbiting Jupiter, 11 normal outer moons and one “oddball,” adding the planet’s total number of known moons to 79, the largest of any planet in the Solar System.
A team led by Carnegie Institution for Science’s Scott S. Sheppard first spotted the moons in the spring of 2017 and Gareth Williams at the International Astronomical Union’s Minor Planet Center used the team’s observations to calculate orbits for the newly found moons.
“It takes several observations to confirm an object actually orbits around Jupiter,” Williams said. “So, the whole process took a year.” According to Carnegie Institution for Science’s news release, nine of the new moons are part of a distant outer swarm of moons that orbit it in the retrograde, or opposite direction of Jupiter’s spin rotation.
These distant retrograde moons are grouped into at least three distinct orbital groupings and are thought to be the remnants of three once-larger parent bodies that broke apart during collisions with asteroids, comets, or other moons.
The newly discovered retrograde moons take about two years to orbit Jupiter. Other two of those new discoveries are part of a closer, inner group of moons that orbit in the prograde, or same direction as the planet’s rotation.
These inner prograde moons all have similar orbital distances and angles of inclinations around Jupiter and so are thought to also be fragments of a larger moon that was broken apart.
These two newly discovered moons take a little less than a year to travel around Jupiter. “Our other discovery is a real oddball and has an orbit like no other known Jovian moon,” said Sheppard. “It’s also likely Jupiter’s smallest known moon, being less than one kilometer in diameter.”
The 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.