The International Astronomical Union (IAU) has announced the discovery of 12 new moons orbiting the largest planet of our solar system - Jupiter. This discovery came from a totally different research project. With 12 more in the cap, the total number of moons orbiting the gas giant has gone up to 79. One of these new moons turned out to be a bit of a rebel. Of the 12 latest moons to join Jupiter’s family, it’s a maverick whose odd orbit may give astronomers crucial insights to understanding how the moons of Jupiter came to be.
Scott Sheppard, an astronomer at the Carnegie Institute of Science, is on a mission to discover Planet Nine, a mysterious object thought to have its orbit beyond Pluto. His team photographs the sky with the finest telescopes of the world, to get a glimpse of the Planet Nine, lurking in the outer reaches of the Solar System. In the spring of 2017, Jupiter was in the part of the sky they wanted to photograph for their research. Sheppard had already been a part of the discovery of 48 moons of Jupiter and is keen researcher of the origin of the Solar System. He realised this was the perfect opportunity to advance two separate research goals with the same telescope data.
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.
“It’s allowed us to cover the whole area around Jupiter in a few shots, unlike before, and we’re able to go fainter than people have been able to go before,” says Sheppard.
Once the Blanco telescope spotted previously unidentified objects near Jupiter, the research team used other telescopes to follow up on these moon candidates and confirm that they were orbiting Jupiter.
The Problem Child
Of all the 12 moons that were discovered, one caught the attention of the team. They're calling it Valetudo. "It’s like it’s going down the highway in the wrong direction." - Sheppard says.
The Jovian moons orbit the planet in a similar fashion as their neighbouring moons. The moon closer to Jupiter - including the 4 Galilean Moons (Ganymede, Io, Callisto, Europa) - orbit Jupiter in the direction of the planet's rotation. Scientists call it prograde motion. The moons far away orbit Jupiter in the opposite direction of its motion - retrograde motion.
Eleven out of twelve moons follow this convention. Valetudo, however, is an exception. It is on the outer orbit of the planet, where the retrograde moons are, and is orbiting in the direction of Jupiter's rotation - prograde motion, driving into the incoming traffic.
Because of it's unusual orbit, astronomers think that Valetudo might have rammed into a retrograde moon, fragmenting into smaller pieces. They're, however, not sure of this theory and need to run supercomputer simulations to calculate how many times an object with Valetudo’s orbit could have collided with the retrograde moons in the solar system’s lifetime.
What Does This Discovery Tell Us?
This observation will give information about the solar system formation and the birth of natural satellites. When Jupiter and the other giant planets were forming, the solar system was a disk and gas and dust that surrounded the infant Sun.
“The giant planets formed out of material that used to be in that region. They were like vacuums, they sucked up all that material and that created the planets,” Sheppard explains. “We think these moons are the last remnants of the material that formed the giant planets.”
When the formation of the Solar System was taking place, chunks of dust and rocks orbited the young Sun. Over the course of time, these chunks formed planets. If any such moon was there around that time, it would have been sucked in my the might gas giant, never to be found again. It is only after the solar system formed, there was enough vacuum, for moons like Valetudo, to orbit this monstrous planet freely.
Once they finish running and analyzing the simulations, the team plans to publish the results in early 2019. In the meantime, they’re waiting for the IAU to formally accept “Valetudo” as the name for the oddball moon.
The IAU requires moons of Jupiter to have names related to the Roman god Jupiter. Valetudo is the name of Jupiter’s great-granddaughter and a Roman goddess of health and hygiene, so it fits the bill. But why hygiene? Sheppard says it comes from an inside joke with his girlfriend.
“I kind of always jokingly say that she’s a very cleanly person; she likes to take multiple showers a day,” Sheppard says. “And so when she told me about Valetudo, which is the goddess of hygiene, I said ‘That’s it, that’s what we’re naming it.’”