A team led by Scott S. Sheppard from Washington DC's Carnegie Institution for Science first spotted the moons in 2017 while on the hunt for a possible massive planet beyond Pluto. While the team did discover 12 new moons, two were announced a year ago.
But one of the newly discovered moons - and the strangest - offers a fresh clue. They are prograde moons, meaning that they orbit in the same direction as Jupiter's rotation. The outer moons move in the opposite direction - a retrograde orbit.
The twelfth moon, however, is rather peculiar.
The team is calling one of the new moons an "oddball" because of its unusual orbit.
This twelfth moon has a wide, 1.5-Earth-year orbit around Jupiter and travels among the retrograde moons. It also has an orbit that runs in the opposite direction and crosses the path of other moons, making head-on collisions between space rocks likely. Several telescopes were used to confirm the finds, including the 6.5-meter Magellan telescope at Carnegie's Las Campanas Observatory in Chile; the 4-meter Discovery Channel Telescope at Lowell Observatory Arizona (thanks to Audrey Thirouin, Nick Moskovitz and Maxime Devogele); the 8-meter Subaru Telescope and the Univserity of Hawaii 2.2 meter telescope (thanks to Dave Tholen and Dora Fohring at the University of Hawaii); and 8-meter Gemini Telescope in Hawaii (thanks to Director's Discretionary Time to recover Valetudo).
Using the Blanco four-metre telescope at Cerro Tololo Inter-American in Chile - which had been recently fitted with a new and highly sensitive instrument called the "Dark Energy Camera", which is about the size of a small vehicle - they detected objects that seemed to be moving against the background stars. The new moons are faint, so researchers haven't been able to spot features on their surfaces or clues to what they're made of.
They take about two years to orbit Jupiter, which is the largest planet in the solar system.
The discovery brings Jupiter's total number of known moons to a whopping 79 - the most of any planet in our Solar System. Two of the newly discovered moons, the ones closest to Jupiter, have prograde orbits, too.
Galileo detected Jupiter's four largest moons, Io, Europa, Ganymede and Callisto in 1610. But the moon Sheppard and his colleagues call "oddball" is different - instead of orbiting with the other prograde moons, its orbit takes it out as far as the retrograde moons.
Most moons, including Earth's, have prograde orbits.
Sheppard's team speculates Valetudo could be a remnant of a collision between one or more moons. Valetudo might be a shattered remnant of one such prograde collider.
The team also discovered one particularly odd moon in the new batch.
Researchers would like to get a close-up look at the moons.
Dr Sheppard said: 'This is an unstable situation. "Head-on collisions would quickly break apart and grind the objects down to dust."Some of Jupiter's moons and moon groupings, including the "oddball", could have formed from collisions like this, according to the statement". Given the moons' stable orbits and kilometer-scale sizes, the collisions were likely chance events later in the solar system's history. "Maybe there will have to be a new definition for the smaller moons". The planet must have acted like a vacuum, sucking up all the material that was around it.Some of that debris was captured as moons.
It's been nicknamed Valetudo after the Roman goddess of health and hygiene who is the great-granddaughter of the god Jupiter.