With 79 moons, Jupiter has by far the greatest number of moons of any planet in our solar system. With the announcement of twelve new moons, eleven of these are classed as ‘normal’ outer moons. The other moon, however, is far more unusual, gaining the term ‘Oddball.’
The moons were first cataloged in 2017 by astronomers, although it has taken another year for the data to be confirmed and for the moons to be internationally ratified. The study that detected the moons was not deliberate; the goal was to look for objects at the very far end of the solar system, to prove or disprove the theory that there is a massive planet out there beyond Pluto. This could be a body nearly the size of Neptune, but as yet unseen.
Detecting moons around Jupiter is challenging. As the largest planet in our solar system, Jupiter has a very large area of influence, which means that there is considerable space where moons could potentially be.
The ‘Oddball’ moon is to be officially called Valetudo, named after the Roman god Jupiter’s great-granddaughter. The reason this Jovian object attracts such interest is because it displays a prograde orbit that crosses the retrograde orbits. With satellites, a retrograde orbit is one where a satellite revolves opposite to its parent body’s direction of rotation. Whereas, a prograde orbit is its opposite; here a satellite revolves in the direction of rotation of the parent object.
The new moon is also probably Jupiter’s smallest known moon, at less than 1 kilometer (0.6 miles) in diameter. While some other moons of Jupiter follow a prograde orbit, these are all inner moons. The newly discovered “Oddball” moon orbits farther from Jupiter than the other moons in the larger prograde group. The moon takes about one and a half Earth years to complete an orbit of the giant planet.
The discovery, which comes from the International Astronomical Union’s Minor Planet Center, is important given that studying the complex influences that shaped a moon’s orbital history can potentially teach scientists more about the solar system’s early years.
