Astronomers Have Discovered a Dozen New Moons Circling Jupiter

And one of them is quite the oddball.

Astronomers looking for Planet Nine-a celestial body predicted to orbit in the outer reaches of our solar system-stumbled upon 12 new moons orbiting Jupiter.

But why are scientists just now finding these moons? And astronomers have just announced the discovery of a dozen more. Instead, scientists will have to wait for a future spacecraft, either flying past Jupiter or orbiting it.

"It's like driving in a vehicle and looking out the window, with highway signs flying by and a mountain in the background moving slowly", Sheppard explained.

One thing that helped was the especially large camera attached to the Blanco telescope. Where their observations had previously been akin to looking through a straw, their capability now is 10 times bigger. Aside from the hulking Galilean moons that stretch thousands of miles in diameter, most of Jupiter's moons, including the new twelve, are between a mile and a few tens of miles across.

The Italian astronomer Galileo Galilei discovered the first four of Jupiter's moons in 1610. Such a collision would quickly break apart and grind the object down to dust, Sheppard said. Now, with a new announcement from a team of astronomers, led by Scott S. Sheppard from the Carnegie Institution for Science, Jupiter's tally now jumps to a total of 79 known moons. "It's also likely Jupiter's smallest known moon, being less than one kilometer in diameter". Two of the newly discovered moons, the ones closest to Jupiter, have prograde orbits, too. Sheppard and his team believe that these moons are remnants of three larger moons that broke apart when they collided with other moons, asteroids or comets.

An illustration showing how the orbits of the newly discovered moons (bold) fit into the known orbital groupings of the Jovian moons (not bold).

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.

And then there's the oddball moon. "Maybe there will have to be a new definition for the smaller moons". Sheppard's girlfriend came up with a name for it: Valetudo, the great-granddaughter of the Roman god Jupiter. As such, the orbit crosses those of the more distant retrograde moons, raising the possibility of a possible head-on collision at some point in the future. It's essentially driving down the highway in the wrong direction, Sheppard explained. Over the course of a billion years, it may even cease to exist.

But the discovery might be short-lived because Valetudo faces destruction in head-on collisions. The latest count of 79 known planets includes eight that have not been seen for several years.

Researchers in the United States stumbled upon the new moons while hunting for a mysterious ninth planet that is postulated to lurk far beyond the orbit of Neptune, the most distant planet in the solar system. It could be as much as 15 times the size of Earth. This putative planet is now sometimes popularly called Planet X or Planet Nine.

Sheppard, Chad Trujillo of Northern Arizona University and David Tholen of the University of Hawaii are on a quest to find as many faint, distant objects on the edge of the solar system as they can. They found a dozen small moons. "We think these moons are the last remnants of the material that formed the giant planets".

So why is this confirmation so hard?

In the meantime, "we have to speculate about what they [the new moons] are made of", Sheppard said. "If one did happen, we would be able to detect it from Earth, but it is unlikely to happen anytime soon".

During its full opposition the planet was brightest in Britain on May between 9:30pm and 4:30am BST while in the USA it peaked on May 9 between 1:10am and 6:20am ET.

  • Joey Payne