10 new moons discovered around Jupiter, but something strange is going on

18 Jul 2018

Image: Vadim Sadovski/Shutterstock

A new bumper haul of moons has been discovered by accident around Jupiter, with one of them described as an ‘oddball’.

Following on from the discovery of two new moons around Jupiter last year, a team of astronomers from Carnegie Mellon University has announced a bumper haul of 10 new moons, bringing the gas giant’s total number to 79.

It now has the largest amount of known moons around a planet in the solar system, but there’s something very peculiar about one of the recently discovered Jovian satellites.

Being less than 1km in diameter, this moon is more distant and more inclined than those found orbiting in the same direction as Jupiter’s rotation (prograde) and would also likely be the planet’s smallest.

Scott S Sheppard, who led the team, described this moon as “a real oddball” because unlike the closer-in prograde group of moons, this particular one has an orbit that crosses the outer moons orbiting in the opposite direction of Jupiter’s rotation (retrograde).

This creates a situation where prograde and retrograde moons are likely to have head-on collisions.

“This is an unstable situation,” Sheppard said. “Head-on collisions would quickly break apart and grind the objects down to dust.”

The team said the likelihood is that the peculiar moon could be the last remnants of a once-larger group of prograde-orbiting moon that would have formed some of the retrograde moon groupings during previous head-on collisions.

Illustration of the new moons orbiting Jupiter

Various groupings of Jovian moons with the newly discovered ones shown in bold. Image: Roberto Molar-Candanosa, courtesy of Carnegie Institution for Science

Finding a name

In terms of what it should be called, one of the leading suggestions has been Valetudo, the goddess of health and hygiene, and the great-granddaughter of the Roman god Jupiter.

The discovery of this collection of moons was actually made by accident as the team had been observing further into space in the hope of finding ‘Planet Nine’, the so-far theoretical planet that could exist at the farthest-flung part of our solar system.

“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,” Sheppard said.

While the hunt for this planet continues, this major moon haul could help piece together more parts of the jigsaw that is the history of the solar system’s earliest years, as elucidating the complex influences that shaped a moon’s orbital history can help reveal this.

Colm Gorey was a senior journalist with Silicon Republic