A research team from the Carnegie Institution for Science, the University of Hawaii and Northern Arizona University was looking in 2017 for very distant objects in our solar system, well beyond Pluto. The scientists embarked on a yearlong process that involved several observations to confirm the moons' existence, according to a Carnegie Institution for Science press release. While the scientists' planet hunt has so far come up dry, the team, using the recently upgraded Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory in Chile, also had Jupiter in view, leading to the discovery. "It's also likely Jupiter's smallest-known moon, being less than 1km (0.6 of a mile) in diameter". The satellite, named for Jupiter's great-granddaughter, could be a bit of unfinished business, the last remnant of the ancient moons that provided the grist for the retrograde cluster, the team theorizes. But the newly discovered moons are tiny, ranging from 1 to 3 kilometers in diameter. They're calling one moon an "oddball" because of its unusual orbit. Jupiter's moons are getting a sense of what that feels like now, with a newly identified resident careening toward conflict with everyone else.
This new "oddball" moon is more distant and more inclined than the prograde group of moons and takes about one and a half years to orbit Jupiter. "They're going around the planet in the opposite direction that Jupiter rotates", Sheppard says.
Astronomers suspect that the retrograde moons may be the remains of larger moons that were destroyed in head-on collisions with prograde objects.
Sheppard, who led the team, said Jupiter just happened to be in the sky near the search fields where they were looking for extremely distant solar system objects so they were serendipitously able to look for new moons around Jupiter at the same time.
"This simulation takes a few months to run and we expect the answer is between about 100 million years and 1 billion years, which is long in human time but not all that long in astronomical time", Sheppard said.
Because Jupiter is also a bright planet, astronomers have had to deal with the issue of glare and scattered light affecting the space where moons can exist. That brings the total number of Jovian moons to 79.
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For example, the discovery that the smallest moons in Jupiter's various orbital groups are still abundant suggests the collisions that created them occurred after the era of planet formation, when the Sun was still surrounded by a rotating disk of gas and dust from which the planets were born. It's out where the outer, retrograde moons are, but it's orbiting Jupiter in the prograde direction, driving into the oncoming traffic.
Astronomers group Jupiter's moons by their distance from the planet as well as their orbital direction.
Our solar system's giant planet has been hiding something - or 12 things, really.
The giant planet region is where the largest planets in our solar system formed, and it's devoid of objects now because the planets gobbled up all of the material to form. If the collisions had happened earlier, the moons would likely have interacted with dust and gas leftover from forming Jupiter and been dragged into the planet.
"If we do find this planet in the next few years, it would be a pretty fantastic discovery for astronomy".
Valetudo is something of an oddball. That means a head-on collision could occur.