Published: Wed, July 18, 2018
Science | By Joan Schultz

By Jove! Astroboffins spot 12 new spanking moons around Jupiter

By Jove! Astroboffins spot 12 new spanking moons around Jupiter

The Cerro-Tololo Inter-American Observatory in Chile is "magnificently desolate", according to astronomer Scott Sheppard.

This image shows the different groupings of moons orbiting Jupiter, with the newly discovered moons displayed in bold.

And that raises a question: Does an object less than a mile across deserve to be called a moon? It's more serious than an icy glare from the front stoop.

"This is an unstable situation", Sheppard said. "It's going to slap into something". Whether that be an exoplanet orbiting a distant star or perhaps a still-unseen planet lurking at the edge of the Solar System, it's a challenging endeavor.

Valetudo, as spotted through the Magellan telescope in May 2018.

As part of that search, Sheppard was using the 4-meter Víctor Blanco Telescope in Chile in March of previous year and realized that Jupiter was right near the part of the sky he wanted to search.

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.

The Blanco 4-meter telescope Sheppard was using is uniquely suited to spotting potential new moons both because the camera installed on it can photograph a huge area of sky at once and because it's particularly good at blocking stray light from bright objects nearby - say, Jupiter - that might wash out fainter ones.

"Our other discovery is a real oddball and has an orbit like no other known Jovian moon", Sheppard explained.

The moons were first discovered during the search for Planet X, the hunt for a massive planet beyond Pluto.

Nine of them, found in the most distant orbits of Jupiter, are in three distinct groups, taking around two Earth years to orbit Jupiter.

As a whole they're not so unusual or remarkable, except, perhaps, for that rogue, Valetudo. They saw a new group of objects moving around the giant gas planet but didn't know whether they were moons or asteroids passing near Jupiter.

Jupiter's moons are arranged in a specific pattern that the giant planet has worked out over time. The largest Galilean moon, Ganymede, is bigger than the planet Mercury. They are prograde moons, meaning that they orbit in the same direction as Jupiter's rotation.

The so-called "oddball" has such a unique orbit that it is at risk of smashing into the other moons - a cosmic collision that could risk wiping the space rocks out. In their recent observations, Sheppard's team documented nine of these (along with two prograde, closer-in moons). Because it is inclined, every so often it crosses the moons that are in retrograde. But every so often, the planets seem to align (no pun intended) and a new discovery just falls right into their laps.

The team suspect the "oddball" is the last-remaining remnant of a once-larger prograde moon that formed some of the retrogrades during past head-on collisions. Along with two found through the same research project but announced in June 2017, this brings the roster of Jupiter's known natural satellites to 79. Over the course of a billion years, it may even cease to exist.

The view from the Chilean mountaintop taught researchers a lot, but there's more to learn. It's not clear when Valetudo will get a close-up, but it ought to be before anything goes splat.

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