Published: Sat, July 21, 2018
Sci-tech | By April Francis

Jupiter Now Has 79 Moons, Astronomers Say

Jupiter Now Has 79 Moons, Astronomers Say

This new "oddball" takes about one and a half years to orbit Jupiter.

It is not a new fact that Jupiter has dozens of moons.

Illustration showing the newly discovered moon (in bold).

The orbit of "oddball" Valetudo, shown in green, compared to the retrograde moons. The moons were accidentally discovered while looking for massive planets beyond Pluto.

Dr Sheppard and colleagues first spotted the moons in spring a year ago while they were looking for very distant Solar System objects as part of the search for the suspected planet on the fringes.

When you're scanning space for a distant planet, that's potentially lurking at the far edges of our solar system, it certainly pays off to keep an eye on what's going on a little closer to home! If there's another planet orbiting the Sun way, way far out - the so-called Planet Nine - then its gravity may affect the orbits of these KBOs, allowing astronomers to figure out where this possible planet is. "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".

Last spring, the scientists were scouring the sky with the Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory in Chile and Jupiter popped in their view, said team leader Scott Sheppard, an astronomer with the Carnegie Institution for Science.

The Carnegie team led by Dr Sheppard first spotted the moons past year while they were searching for a giant planet orbiting the sun beyond Pluto.

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

The study suspects that Valetudo is the final remnant of a once much larger moon that has been ground to dust by collisions in the past. It's essentially driving down the highway in the wrong direction, Sheppard explained. Astronomers believe that prograde moons form around a planet from the same cloud of dust and gas, which is why they tend to have closer orbits and matching rotation. If moon circles a planet in the opposite direction of a rotating planet, that orbit is retrograde. This swarm may have originally been three separate moons that broke apart after collisions.

It takes around 18 months to orbit Jupiter, and its orbit passes that of the retrograde moons, which makes collisions pretty likely. The moon Valetudo is in the retrograde cluster, but it orbits in a prograde direction and crosses the orbits of several other satellites.

The researchers believe the oddball may be a leftover fragment from a larger prograde moon that split apart from repeated collisions.

Finding lots of these small moons also tells us about conditions in the early solar system. Surprisingly, some unknown and very faint objects appeared around the gas giant.

"The giant planets formed out of material that used to be in that region".

Sheppard says Jupiter's prograde moons probably formed from the same spinning disk of stuff that eventually coalesced to form the planet. What's truly weird is that this set up prone to four moon-to-moon collisions.

If we were to host a system-wide beauty contest among the planets and accepted natural satellites as a valid skill, Jupiter would have a pretty unfair advantage. "Most of the small objects that helped build the planets we see today were incorporated into the planets themselves, and these moons are all that remains", Sheppard wrote.

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