Because the planet is so big and bright, researchers surmised that unrecorded moons could be faint, or even obscured, or quite far from the gas giant. Sheppard, who is broadly interested in the formation of solar systems and has been involved in the discovery of 48 of Jupiter's known moons, realized this was the flawless opportunity to advance two separate research goals with the same telescope data.
In 2014, this same team found the object with the most-distant known orbit in our Solar System and was the first to realize that an unknown massive planet at the fringes of our Solar System, far beyond Pluto, could explain the similarity of the orbits of several small extremely distant objects. Nine objects, which are in three different groups, are likely the remnants of larger moons that broke apart during collisions. The "oddball" with the proposed name Valetudo orbits in the prograde, but crosses the orbits of the planet's outer retrograde moons.
The 12th moon is being called an oddball because, while it orbits in the same direction as Jupiter's spin, it is much farther away than the others orbiting in that direction and it is comparatively tiny.
A head-on collision between two moons would "grind the objects down to dust", he added.
During a quest to find Planet Nine, a mysterious planet believed to be on the edge of our solar system, astronomers discovered something else: 12 new moons around Jupiter. If moon circles a planet in the opposite direction of a rotating planet, that orbit is retrograde. "This suggests our own Jupiter may have influenced terrestrial planet formation in an atypical fashion".
After the team of scientists initially saw the moons via a telescope at Chile's Cerro Tololo Inter-American Observatory, at least four other telescopes were used to verify the moons.
The chance find brings the gas giant's tally of moons to 79 - 17 more than Saturn, the planet with the second most orbiting moons in the solar system. "So, the whole process took a year". In 2017, the group reported two additional Jovian moons. Aside from the hulking Galilean moons that stretch thousands of miles in diameter, most of Jupiter's moons, including the new twelve, are between a mile and a few tens of miles across. One moon is located in the outer group but orbits in the opposite direction. While the team did discover 12 new moons, two were announced a year ago. The solar system's ocean worlds might be the most promising place to look. Others including the oddball are "pro-grade" moons travelling with the planet's spin.
It is possible the various orbital moon groupings we see today were formed in the distant past through this exact mechanism.
The oddball is also the smallest of the moons that Sheppard and his colleagues found, just 1 kilometer across. The satellite, named for Jupiter's great-granddaughter, could be a bit of unfinished business, the last remnant of the ancient moons that provided the grist for the retrograde cluster, the team theorizes.
During its full opposition the planet was brightest in Britain on May between 9:30pm and 4:30am BST while in the United States it peaked on May 9 between 1:10am and 6:20am ET. "They're going around the planet in the opposite direction that Jupiter rotates", Sheppard says.