Astronomers find 12 new moons around Jupiter

Pablo Tucker
July 18, 2018

Three groupings of Jupiter's moons with a dozen newly discovered ones shown in bold.

But Sheppard suspects these moons could be holdouts, the "last remnants" of early solar system objects.

Valetudo, as spotted through the Magellan telescope in May 2018. With a total of 79 moons, Jupiter is now the most lunar-rich planet in the solar system. Of the twelve, only three moons orbit in a prograde direction, and are closer to Jupiter.

These new moons probably formed in a place in our solar system known as the giant planet region, which is between the asteroid belt, dominated by rocky asteroids, and the Kuiper belt, dominated by icy comets.

The 2 new regular prograde moons join 15 other previously discovered prograde satellites that typically orbit Jupiter in about an Earth year or less. 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.

"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", Scott Sheppard, an astronomer at the Carnegie Institution for Science, said in a news release. The 12th moon, however, is described as "a real oddball", because of its unique orbit and because it is also probably Jupiter's smallest known moon, at less than 1 kilometer (0.6 miles) in diameter, Sheppard said in the statement.

It doesn't behave like the other moons, which tend to fall into a few categories. "It is moving prograde while all the other objects at a similar distance from Jupiter are moving retrograde".

In addition to these two groups, Jupiter has "regular" satellites, or moons with almost circular orbits.

This moon, now called Valetudo, moves in a prograde motion, though it is slightly inclined compared to the orbits of the other moons.

Sheppard, whose report appears in the International Astronomical Union Minor Planet Electronic Circular, suspects that Valetudo is the final remnant of a once much larger moon that has been ground to dust by collisions in the past.

In June 2017, the same team discovered two mile-wide moons and five lost moons. TheyÂre calling one moon an ‘oddball because of its unusual orbit.

"Valetudo's going down the highway the wrong way, so it's very likely it will collide with these other objects". Confirmation of the moons required multiple observations, and those data enabled a calculation of the moons' orbits. Given the moons' stable orbits and kilometer-scale sizes, the collisions were likely chance events later in the solar system's history. The best forecast, for now, is some time in the next billion years. If you said 69, you were right.

The view from the Chilean mountaintop taught researchers a lot, but there's more to learn.

"It's not hugely surprising to me, I think as we look deeper, we'll find more of these irregular satellites around Jupiter, Saturn, Uranus and Neptune, but it is cool, and it's great that they've found so many all at once".

But the researchers realized that Jupiter happened to be in a spot that allowed them to examine the area around the gas giant for any unknown natural satellites. They could be rock, ice or a mixture. It's not clear when Valetudo will get a close-up, but it ought to be before anything goes splat.

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