How a Desert Mountain Telescope Revealed Jupiter's Odd New Moon

Rodiano Bonacci
Luglio 18, 2018

The researchers confirmed two new moons among the inner prograde moons.

More than 400 years after Galileo Galilei discovered the first of Jupiter's moons, astronomers have found a dozen more - including one they've dubbed "oddball" - orbiting the planet.

After their observations and more than a year of follow-ups and confirmations, they announced this week that they found 12 new moons.

"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, a researcher at the Carnegie Institution for Science, a private, nonprofit organisation based in Washington, D.C.

Using the Blanco 4-meter telescope at Cerro Tololo Inter-American in Chile, with its highly-sensitive Dark Energy Camera, however, gave the team a distinct advantage.

"It takes several observations to confirm an object actually orbits around Jupiter", Gareth Williams at the International Astronomical Union's Minor Planet Center, said in a statement. Those moons orbit close to Jupiter and travel in the same direction as the planet spins.

The newly discovered moons await naming, a task for which the public may be enlisted, so it's a good idea to brush up on the IAU's naming rules for Jovian moons - and which names have already been taken. Sheppard believes it could be Jupiter's smallest, and it has an orbit unlike any other moon around the planet. The name Valetudo has been proposed for it, after the Roman god Jupiter's great-granddaughter, the goddess of health and hygiene. 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.

The team also discovered one particularly odd moon in the new batch.

The curious find might shed light on how many of Jupiter's current moons were formed. It orbits Jupiter in and amongst where the retrograde moons reside, however, it follows a highly risky prograde orbit as it does so.

The effect of opposition is similar to the effect of the full moon seen once a month when Earth is positioned directly between our natural satellite and the sun. 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. Of the twelve, only three moons orbit in a prograde direction, and are closer to Jupiter. Maybe 100 or more of the really small ones. But the newly discovered moons are tiny, ranging from 1 to 3 kilometers in diameter.

These two groups of prograde and retrograde moons consist of "irregular" satellites, or moons whose orbits have irregular, or noncircular, shapes. Sheppard expects there could be even more small moons lurking out there. If a moon circles in the same direction as a planet's rotation, that moon's orbit is called prograde.

"Jupiter is like a big vacuum cleaner because it's so massive", Sheppard said.

One of these new moons turned out to be a bit of a rebel. "These objects are probably some intermediate-type composition, half-rock and half-ice, something like that". "We think these moons are the last remnants of the material that formed the giant planets".

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