Scientists have discovered 12 new moons orbiting Jupiter, bringing the known total to 79 - the most of any planet in our solar system.
Eleven of the moons found were "normal" outer moons, along with one that astronomers are calling an "oddball".
Led by Carnegie Institution for Science's Scott Sheppard, along with the University of Hawaii's Dave Tholen and Northern Arizona University's Chad Trujillo, the team of scientists first spotted the moons in spring Last year of 2017 while they were looking for very distant Solar System objects as part of the hunt for a possible planet far beyond Pluto, now sometimes popularly called Planet X or Planet Nine.
"Jupiter just happened to be in the sky near the search fields where we were looking for extremely distant Solar System objects, so we were serendipitously able to look for new moons around Jupiter while at the same time looking for planets at the fringes of our Solar System," said Sheppard.
However, it took a year to confirm the satellites were actually moons of Jupiter as it apparently takes several observations to confirm an object actually orbits a planet.
The astronomers said that nine of the new moons are part of a distant outer swarm of moons that orbit it in the retrograde, or opposite direction of Jupiter's spin rotation. These distant retrograde moons are grouped into at least three distinct orbital groupings and are thought to be the remnants of three once-larger parent bodies that broke apart during collisions with asteroids, comets, or other moons.
They found that the newly discovered retrograde moons take about two years to orbit Jupiter.
Two of the new discoveries are also part of a closer, inner group of moons that orbit in the prograde, or same direction as the planet's rotation. These inner prograde moons all have similar orbital distances and angles of inclinations around Jupiter and so are thought to also be fragments of a larger moon that was broken apart.
It's observed that these two newly discovered moons take a little less than a year to travel around Jupiter.
However, there's also a new "oddball" moon that is more distant and more inclined than the prograde group of moons and takes about one and a half years to orbit Jupiter. Unlike the closer-in prograde group of moons, this new oddball prograde moon has an orbit that crosses the outer retrograde moons.
"Our other discovery is a real oddball and has an orbit like no other known Jovian moon," Sheppard explained. "It's also likely Jupiter's smallest known moon, being less than one kilometer in diameter".
As a result, head-on collisions are much more likely to occur between the "oddball" prograde and the retrograde moons, which are moving in opposite directions.
"This is an unstable situation," said Sheppard. "Head-on collisions would quickly break apart and grind the objects down to dust."
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