This now brings the total number of moons around the planet to 79 - the largest number of moons of any planet within our solar system. Only the two innermost planets in the solar system, Mercury and Venus, have none.
The researchers, from the Carnegie Institution for Science in Washington, DC, picked out one of the 12 moons as an "oddball".
It's easy to understand why these 12 new additions had been missed so far.
Astronomer Scott Sheppard of the Carnegie Institution for Science is on the hunt for Planet Nine, a hypothetical planet many astronomers think should exist in the distant reaches of our Solar System, beyond Pluto.
Jupiter as seen from Hubble. The circumstances of the moons' orbits lend further support to the view that they were formed long after Saturn and its larger moons coalesced from a primordial cloud of gas and dust. Two of the discoveries are part of an inner group in the prograde that orbit in the same direction as the planet's rotation.
Our solar system is full of moons of many different kinds, just as diverse and incredible as the planets they orbit.
But these moons orbit clockwise, indicating a different formation mechanism. Because they are most likely clues to the origins of the planet itself. When moons move all in the same direction, collisions are less likely, like when a bunch of cars are all driving in the same direction on one side of the highway. It was probably forming in the giant planet region and grew to be several Earth masses in size, and then it got close to one of the giant planets and was thrown out into the outer solar system. The other three are prograde, which orbit in the same direction.
Once they finish running and analyzing the simulations, the team plans to publish the results in early 2019.
The team is calling one of the new moons an "oddball" because of its unusual orbit.
"It's also likely Jupiter's smallest known moon, being less than one kilometre in diameter".
Valetudo, as the team calls this oddball moon, is named after the Roman goddess of health, cleanliness and hygiene. What makes it odd, however, is its maverick orbit: it is the only prograde Jovian satellite discovered to date to orbit at the same distances as the retrograde moons.
Before Sheppard's team conducted their survey, there were 69 known Jovian moons, but there's always been reason to believe there are quite a few more. This means it crosses paths with the outer retrograde moons and could collide with them. "Magnificent desolation", Sheppard says, is the ideal.
These distant "retrograde" moons are thought to be the remnants of three once-larger bodies that broke apart during collisions with asteroids, comets, or other moons. Scientists believe it could be the last remaining remnant of a once larger moon that was involved in past collisions.
Astronomers are still finding moons at Jupiter, 400 years after Galileo used his spyglass to spot the first ones.
Overall, this was a tough, but very rewarding discovery. "We know nothing, really, more than that".