Scientists have discovered 12 previously unknown moons orbiting Jupiter, and one of them is a real oddball.
While hunting for the proposed Planet Nine, a massive planet that some believe could lie beyond Pluto, a team of scientists, led by Scott Sheppard from the Carnegie Institution for Science, found the 12 moons orbiting Jupiter. With this discovery, Jupiter now has a staggering 79 known orbiting moons — more than any other planet in the solar system.
Of the 12 newly discovered moons, 11 are “normal,” according to a statement from the Carnegie Institution for Science. The 12th moon, however, is described as “a real oddball,” because of its unique orbit and because it is also probably Jupiter’s smallest known moon, at less than 1 kilometer (0.6 miles) in diameter, Sheppard said in the statement. [Photos: The Galilean Moons of Jupiter]
In the spring of 2017, these researchers were searching for Planet Nine in the region past Pluto, and “Jupiter just happened to be in the sky near the search fields where we were looking,” Sheppard said. This gave the team a unique opportunity to search for new moons around Jupiter in addition to objects located past Pluto, according to the statement.
Nine of the newly discovered moons have retrograde orbits, meaning that they orbit in the opposite direction of the planet’s spin. These satellites are part of a large group of moons that orbit in retrograde far from Jupiter. In fact, of Jupiter’s 67 previously discovered moons, the 33 outermost moons all have retrograde orbits.
Two of the newly discovered moons orbit much closer to Jupiter and have a prograde orbit, meaning that they orbit in the same direction as the planet. These are part of a group of prograde moons that orbit closer to Jupiter than the retrograde moons do. Most of these prograde moons take less than a year to travel around the planet.