The other nine moons, grouped in clusters of three, have retrograde orbits.
The find came when scientists were looking for objects on the outer edge of the solar system but then turned the telescopes toward Jupiter, according to Scott Sheppard of the Carnegie Institute for Science in Washington. But in practice, astronomers only count objects whose orbits they can determine.
The moons had not been spotted before because they are tiny. So the researchers had to continue observations.
One of these new moons turned out to be a bit of a rebel. Jupiter is not in the frame and is off to the upper left. But, the faith had other plans for the scientists and exposed 12 new moons orbiting Jupiter to them. However, during the hunt, researchers caught glimpse of the moons back in March of 2017 but needed to confirm whether they were actually locked in orbit with Jupiter. Valetudo is the goddess of health and hygiene, which can not help with this little oddball moon's self-confidence. These moons include the famous Galileans: Io, Europa, Ganymede, and Callisto. "It took a year to figure out what these objects were".
There are outer prograde moons, as well.
The 10th new moon is the oddball. They are part of a larger swarm of moons orbiting a long distance out from Jupiter.
Astronomers think retrograde moons have a different origin story from prograde moons, which travel in the same direction that their planet rotates. This individualistic path could lead to more head-on collisions between the "oddball" prograde and the retrograde moons, which are moving in opposite directions. But every so often, the planets seem to align (no pun intended) and a new discovery just falls right into their laps.
Carnegie Institute MYSTERY The new'oddball moon has intrigued boffins
Most of the moons are the size of large asteroids, measuring between one and three kilometers (about two-thirds of a mile to two miles) in diameter.
"It's basically driving down the highway in the wrong direction", Sheppard said.
Even better, they were found as a kind of bonus. The astronomers are now running computer simulations to determine how the ancient moons fragmented.
"Over a human lifetime, it doesn't happen".
However, don't hold your breath waiting to witness Valetudo crash with one of its neighbors-Sheppard has said that collisions only occur about once in a billion years.
Interestingly, the astronomers believe that this is what happened in the past. Sheppard says these retrograde moons were probably objects that were once wandering around the solar system.
"This just shows how chaotic our solar system was in the past". Understanding that smaller moons still exist in the outer regions of Jupiter's orbital regions suggests to astronomers that they formed after the planets. They're thought to have formed after the gas and dust from the earliest stages of planetary formation had dissipated.
The realm of the giant planets - between Jupiter, Saturn, Uranus and Neptune - is largely devoid of small objects. Sheppard expects there could be even more small moons lurking out there.