Scientists have discovered 12 new moons orbiting the gas giant Jupiter bringing its total number of natural satellites to 79—the most of any planet in the Solar System.
Eleven of the new discoveries are "normal" outer moons, while one has been described as an "oddball" by a team of scientists led by astronomer Scott S. Sheppard from the Carnegie Institution for Science.
The researchers first spotted the moons in the spring of 2017 while they were searching for objects in the farthest reaches of the solar system as part of a project to find a massive hypothetical planet beyond the orbit of Pluto, known as Planet Nine or Planet X.
Jupiter just happened to be in the sky near the fields-of-view in which the team were searching, enabling them to also look for new moons.
"Our survey [used] a new powerful camera on a large telescope that allowed us to image around Jupiter deeper than others have to date," Sheppard told Newsweek. "Thus we could find fainter and smaller objects that previous surveys could not."
After the discovery of the moons, scientists from the International Astronomical Union's Minor Planet Center used the team's data to calculate their orbits—a process that required several observations taken over the course of a year.
Of the new moons, nine are part of a group that orbit Jupiter every two Earth years at a large distance and in the opposite direction to the planet's spin rotation (retrograde orbit). Because these "retrograde" moons have coalesced into three different orbital groupings, they are thought to be the remnants of three larger, precursor worlds that broke up as a result of collisions with asteroids, comets or other moons.
Meanwhile, two of the moons form part of an inner group that orbit Jupiter closer and in the same direction as the planet's rotation (prograde orbit), taking just less than an Earth year to complete a full cycle. Because these "prograde" moons all orbit Jupiter at similar distances and angles of inclination, scientists think that the pair may originate from a single larger moon that also broke apart.
The final, newly discovered moon—which has been dubbed "Valetudo" after the great-granddaughter of the Roman god Jupiter—is the most intriguing, according to the researchers.
"Our other discovery is a real oddball and has an orbit like no other known Jovian moon," Sheppard said in a statement. "It's also likely Jupiter's smallest known moon, being less than one kilometer in diameter."
The "oddball" is a prograde moon and takes around an Earth year-and-a-half to orbit Jupiter, at a greater distance and inclination than the other prograde moons. Intriguingly, its orbit crosses those of the outer retrograde moons.
"Valetudo is driving down the highway on the wrong side of the road," Sheppard said. "That is, it is moving prograde while all the other objects at a similar distance from Jupiter are moving retrograde. Thus head-on collisions are likely."
Valetudo likely collided with some of the retrogrde moons in the past and what we see today is the last remnant of a once, much larger world that has slowly been ground down.
Understanding the history of moons such as these can provide scientists with insights into the early years of our Solar System.
"These moons are the last remnants of the objects that the planets were built from," Sheppard said. "So understanding these moons helps us understand what the planets were originally made from."
This article has been updated to include additional comments from Scott S. Sheppard.
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