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. And astronomers have just announced the discovery of a dozen more.
All the newly identified moons are relatively small.
That brings the number of moons at Jupiter to 79, the most of any planet.
But cosmic serendipity placed the moons in front of their telescope.
Using the 4-meter Víctor Blanco Telescope in Chile, the team really hit the moon jackpot.
From Jupiter's entire collection of 79 moons, Sheppard has been involved in the discovery of 54 of them, including most of the known retrograde moons. "It was a long process", said Scott Sheppard, who led the effort at the Carnegie Institution for Science in Washington DC.
It means Jupiter, the oldest and largest planet in the solar system, has more moons than any of the other seven.
Galileo detected Jupiter's four largest moons, Io, Europa, Ganymede and Callisto in 1610.
Two of the new moons are found closer to Jupiter, orbiting the gas giant in prograde - in the same direction as Jupiter's spin. The smallest moon is just over a half-mile across, while the largest is about three miles in diameter.
Scientists have discovered 12 previously unknown moons orbiting Jupiter, and one of them is a real oddball. Researchers at the International Astronomical Union's Minor Planet Center used Sheppard's team's data to estimate when another collision might happen. They also are thought to be the result of an earlier collision and take about a year to complete one orbit.
Size isn't a requirement to be a moon - there's no such thing as a dwarf moon.
"Valetudo is like driving down the highway on the wrong side of the road", said Sheppard.
A research team from the Carnegie Institution for Science, the University of Hawaii and Northern Arizona University was looking in 2017 for very distant objects in our solar system, well beyond Pluto.
If these raw materials had still been present when Jupiter's first moons collided to form its current clusters, the drag exerted on the smaller ones would have made them spiral inwards. But then there was one more, a moon the researchers term the "oddball" of the bunch. Understanding that smaller moons still exist in the outer regions of Jupiter's orbital regions suggests to astronomers that they formed after the planets.
Two of the new discoveries are part of a closer, inner group of moons that orbit in the prograde, or same direction as the planet's rotation.
There are outer prograde moons, as well. They have proposed to call the new moon Valetudo, named after the great-grandaughter of the Roman god Jupiter, the goddess of health and hygiene.
Finally, there are retrograde moons.
Valetudo is something of an oddball. They are part of a larger group, all with similar distances and angles of inclination, taking little less than a year to orbit Jupiter. What's more, those orbits intersect.
It doesn't behave like the other moons, which tend to fall into a few categories.
They all turned out to be moons of Jupiter.
The realm of the giant planets - between Jupiter, Saturn, Uranus and Neptune - is largely devoid of small objects. By contrast, retrograde moons were probably objects that once were wandering around the solar system and got snared by Jupiter's gravity.