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.
"It takes several observations to confirm an object actually orbits around Jupiter", Gareth Williams at the International Astronomical Union's Minor Planet Center, said in a statement. Unfortunately, they couldn't find the hypothesized planet using the Blanco 4-meter telescope at Cerro Tololo Inter-American in Chile, but they did manage to unearth a treasure trove of new satellites around our largest planet.
Scientists classified the findings as 11 "normal" outer moons, and another that they are calling an "oddball" for its unusual orbit.
Outside the orbits of the prograde moons is the largest group, the retrograde moons, which orbit around Jupiter in the opposite direction to the planet's spin.
The 12th new moon is a bit of an oddball, Sheppard said, with "an orbit like no other known Jovian moon".
And he thinks Jupiter might have even more moons just as small waiting to be found. This brings Jupiter's total number of known moons to a whopping 79-the most of any planet in our Solar System.
In June 2017, the same team discovered two mile-wide moons and five lost moons. These satellites are part of a large group of moons that orbit in retrograde far from Jupiter. Confirmation came with help from a variety of observatories, including the 6.5-metre Magellan telescope at Carnegie's Las Campanas Observatory in Chile, the 4-metre Discovery Channel Telescope at Lowell Observatory in Arizona, the 2.2-metre University of Hawaii telescope and the 8-metre Subaru and Gemini Telescopes, also in Hawaii.
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The orbit of "oddball" Valetudo, shown in green, compared to the retrograde moons. It's out where the outer, retrograde moons are, but it's orbiting Jupiter in the prograde direction, driving into the oncoming traffic. Since it's more distant than the other prograde moons, the oddball crosses the path of outer retrograde moons. That means the revolve around Jupiter opposite from the planet's rotation.
It's further away than the prograde moons, taking around one and a half years to orbit around the planet. It was probably right in the middle of the planets we know so well, Sheppard said. Sheppard's team speculates Valetudo could be a remnant of a collision between one or more moons. By this latest count, our solar system's largest planet now has 79 moons, more than any other. "Head-on collisions would quickly break apart and grind the objects down to dust". "They also are fragments of the early solar system before the planets were formed, which makes studying them important to learning about the solar system's history". At the same time, they watched for Planet Nine or smaller, distant dwarf planets in the background. The telescope recently was upgraded with the Dark Energy Camera, making it a powerful tool for surveying the night sky for faint objects.
"Jupiter was well-placed in the sky to kill two birds with one stone", Sheppard said.
This was at a time when the Sun was still surrounded by a rotating disc of gas and dust from which the planets were born.
The twelve moons have been broadly clustered into three groups.
One moon in particular caught the researchers' attention.