Scientists were looking for objects on the fringes of the solar system a year ago when they pointed their telescopes close to Jupiter's backyard, according to Scott Sheppard of the Carnegie Institute for Science in Washington.
"It takes several observations to confirm an object actually orbits around Jupiter", Gareth Williams at the International Astronomical Union's Minor Planet Center, said in a statement. The moon, tentatively named Valetudo, also has a more inclined orbit than other prograde moons and is one of the smallest moons of Jupiter discovered to date, measuring less than 1 kilometer in diameter.
"This is an unstable situation", said Sheppard. "Head-on collisions would quickly break apart and grind the objects down to dust".
The researchers believe the oddball may be a leftover fragment from a larger prograde moon that split apart from repeated collisions. It has a prograde orbit like the closer group of moons, but during its trip around Jupiter, it crosses into the paths of those retrograde moons, resulting in an orbit that takes around one-and-a-half years to complete.
This moon, now called Valetudo, moves in a prograde motion, though it is slightly inclined compared to the orbits of the other moons.
"There was no eureka moment", said Sheppard, who led the team of astronomers.
At less than two miles (3.2km) wide, the moons are all very small, which is why they have only now been identified thanks to the team's modern, sensitive telescopes.
"It's not hugely surprising to me, I think as we look deeper, we'll find more of these irregular satellites around Jupiter, Saturn, Uranus and Neptune, but it is cool, and it's great that they've found so many all at once". And with Jupiter being the biggest planet in our solar system, astronomers need to be able to see as much of the space around it as possible.
Nine of the new moons belong to an outer "retrograde" swarm circling against the direction of Jupiter's rotation.
They saw a new group of objects moving around the giant gas planet but didn't know whether they were moons or asteroids passing near Jupiter. Sheppard's team speculates Valetudo could be a remnant of a collision between one or more moons.
While searching for a hypothetical planet at the far edges of our solar system known as Planet Nine or Planet X, a team of astronomers discovered 12 new moons around Jupiter. They are also part of a larger group of small moons thought to be the left-over remnants of a once larger moon.
The moons are now known by their numerical designations, such as S/2016 J2. Valetudo is the name of Jupiter's great-granddaughter and a Roman goddess of health and hygiene, so it fits the bill.
This orbital arrangement means Jupiter appears as the largest disc in the sky and will be visible from sundown to sunrise.
These building blocks of planets can provide a window into the early years of the solar system.
"If we do find this planet in the next few years, it would be a pretty awesome discovery for astronomy". The telescope recently was upgraded with the Dark Energy Camera, making it a powerful tool for surveying the night sky for faint objects. Their existence shows that they were likely formed after this gas and dust dissipated.