From The Editors Science

Astronomers Identify 12 News Moons Orbiting Jupiter – One of them a Real “Oddball”

Researchers at the Carnegie Institute for Science in Washington D.C., on Tuesday (July 17) announced the discovery of a dozen new moons orbiting Jupiter, by far the largest planet in our solar system, in terms of, both, mass and volume.

The discovery was purely accidental, as researchers were, in fact, scanning the edge of the solar system, way beyond Neptune’s orbit, for a mysterious ninth planet when they stumbled upon these 12 moons, taking the tally of known Jovian satellites to 79.

“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 Scott Sheppard – an astronomer in the Department of Terrestrial Magnetism at the Carnegie Institute and the team lead of the group that found the moons.

Now, seventy-nine moons may sound like one too many for a planet to have moving around it, but when you consider Jupiter’s massive size and girth, its diameter 11.2 times that of earth’s, you get the feeling that there are more such moons waiting to be discovered.

Saturn, which measures 116,464 kilometers in a diameter compared to Jupiter’s 139,822 kilometers, has 62 natural satellites, the same number that Jupiter had before the serendipitous discovery of a dozen new ones.

Calling the accidental discovery “fascinating,” planetary scientist Doug Hemingway of the University of California, Berkeley, said that it was “a great reminder that when you build up the capability to study one thing, you never know what else you might discover along the way.”

With two moons having been spotted earlier, ten of the new Jovian satellites were first chanced upon back in March 2017 when Sheppard and his fellow researchers were looking beyond the outer reaches of the solar system for Planet X.

When Sheppard and his colleagues realized that Jupiter happened to be within the range of the  Blanco telescope at Chile’s Cerro Tololo Inter-American Observatory, they decided to make the most of the opportunity while they were at it.

“We’re using a new camera that was only put on the telescope a few years ago,” Sheppard said, adding that the camera’s capability to quickly search large areas made it possible for them to cover the entire area surrounding the huge planet using just four images.

The reason it took as long as it did to announce the findings is that the researchers needed to be absolutely sure that the Jovian bodies were actually locked in orbit around Jupiter, which can be a fairly time-consuming process.

“It was a long process,” Sheppard said.

While the objects circling Jupiter moved at the same rate as the planet itself, which is pretty fast, the far-flung objects in the solar system were much slower in comparison, making it easy for the researchers to differentiate between the Jovian bodies and the distant objects.

“It’s like driving in a car and looking out the window, with highway signs flying by and a mountain in the background moving slowly,” explained Sheppard.

“You can see both at the same time and easily tell the difference between the two,” he added.

Nine of the new satellites move around Jupiter at a distance of 25 million kilometers in retrograde orbits, meaning they move in the opposite direction of the planet’s rotation, completing an orbit in twice the time that earth takes to orbit the sun.

Sheppard and his colleagues have reasons to believe that these moons are parts of three larger ones that disintegrated after colliding with comets, asteroids, or other moons.

Two moons of the remaining three, are closer to the gas giant and move in the direction of the planet’s rotation, known as prograde orbit.

Their angle and distance from their parent planet hint at the possibility of the two also being parts of a larger moon that happened to break up for some celestial reason. Their orbit time is less than an earth year.

We saved the twelfth and the last of Jupiter’s new moons for the end because it is the smallest, yet the most intimidating of the twelve – a rogue moon if you like – and, hence, it deserves a dedicated space.

No larger than half a mile in diameter, this bizarre little moon, which the researchers have named Valetudo, after the Roman god Jupiter’s great-granddaughter, could be the smallest of all of Jupiter’s 79 known moons, not just smallest among the twelve, believes Sheppard

However, as small as it is, it can most likely spell the doom of the other moons, as well as itself, because its distance and incline of orbit take it across the paths of the outer retrograde moons, basically meaning that collision at some point is imminent.

Sheppard uses the ‘driving down the wrong side of the road’ analogy to good effect to explain the clear and present danger of a violent collision.

“It’s like if you’re driving down the highway the wrong way,” he says. “Collisions are very likely to happen.”

There is a high probability that Valetudo has been in some major collisions in the past, losing chunks of mass to become the size it is today; and, at this rate, it won’t take more than a billion years for it to become a swirling mass of debris around Jupiter.

“Valetudo was probably much bigger at one point, perhaps as much as tens of kilometers in diameter, but it likely collided with one of the original parent retrograde objects and broke it apart,” Sheppard said.


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