Astronomers searching for signs of a large planet far beyond Pluto have stumbled across 12 previously undetected moons orbiting Jupiter, pushing the giant planet's total to a record 79, the Carnegie Institution reported Tuesday.

"Jupiter just happened to be in the sky near the search fields where we were looking for extremely distant solar system objects," Scott Sheppard, leader of the Carnegie team, said in a statement. "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."

Nine of the newly discovered moons are part of an outer group that orbit in the opposite, or retrograde, direction of Jupiter's spin, taking about two years to complete one trip around the planet. The new moons were found in three distinct clusters and are thought to be debris left over when three larger bodies were broken apart in earlier collisions.

Two previously undetected moons were found closer in, part of a group that orbits in the same "prograde" direction as Jupiter's rotation. With orbital periods of about one year, they also are thought to be the result of earlier collisions.

Sheppard described the 12th new moon as an "oddball" with "an orbit like no other known Jovian moon. It's also likely Jupiter's smallest known moon, being less than one kilometre (0.62 miles) in diameter."

Dubbed Valetudo after the Roman god Jupiter's great-granddaughter, the tiny moon orbits in the prograde direction but at a greater distance from Jupiter, taking about a year and a half to complete one trip around the planet. As such, the orbit crosses those of the outer retrograde moons, raising the possibility of a possible head-on collision at some point in the future.

"This is an unstable situation," said Sheppard. "Head-on collisions would quickly break apart and grind the objects down to dust."</s>10 Moons Orbiting Jupiter Discovered, One 'Oddball' on a Collision Course

In 2014, the same team of scientists found the object with the most-distant known orbit in the Solar System and was the first to hypothesize the existence of a putative planet popularly called Planet X or Planet Nine</s>Ten new moons—including one ‘oddball’—discovered around Jupiter

Jupiter’s orbital family has just rapidly expanded, with scientists today announcing the discovery of 10 new miniature moons around the gas giant. That brings its total known satellites to 79, the most in the solar system.

The new moons, pictured as circles above, were discovered last year by a team of astronomers. After verification, they are being reported today by the International Astronomical Union, based in Paris. At the time, the researchers were searching for a theorized massive planet far beyond Pluto, known as Planet X or Planet Nine, which is thought to be tugging on the orbits of distant solar system objects. Although the scientists’ planet hunt has so far come up dry, the team, using the recently upgraded Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory in Chile, also had Jupiter in view, leading to the discovery. Additional observations over a year confirmed the orbits of the moons, all of which are 3 kilometers or less in diameter.

The moonlets mostly follow Jupiter’s known patterns: Located far beyond the planet’s large primary moons (purple), two of the new moonlets belong to a grouping (blue) that spins in the same direction as the planet, all of which are believed to be the fragments of one large shattered moon. Seven fall in a farther out “retrograde” cluster (red) rotating against the planet’s spin, their opposing path kick-started when ancient moons collided with comets, asteroids, or other moons.

But one moon, tentatively dubbed “Valetudo” (green), is an oddball, orbiting with Jupiter’s spin but within the retrograde cluster. The satellite, named for Jupiter’s great-granddaughter, could be a bit of unfinished business, the last remnant of the ancient moons that provided the grist for the retrograde cluster, the team theorizes. Its path weaving within the retrograde moons is unstable, they add; a collision, at some point, is likely.

*Correction, 17 July, 10:30 a.m: An earlier version of this article misstated the number of new moons discovered. Although the team did discover 12 new moons, two were announced last year.</s>Jupiter, the solar system's biggest planet, still has many mysteries left to uncover. New research finds 12 additional moons orbiting the planet, bringing the total to 79 moons. (Photo : NASA | JPL-Caltech | SwRI | MSSS | Kevin M. Gill)

Jupiter has dozens and dozens of moons in its orbit, but another 12 has just been discovered — including an "oddball" with a precarious orbit.

The gas giant now has a total of 79 known moons, by far the most of any planet in the solar system.

Carnegie Institution for Science reports that out of the 12 newly discovered moons, 11 appear totally normal.

Nine moons are part of the planet's outer swarm of moons, orbiting in retrograde or in the opposite direction of Jupiter's spin rotation. These take two years to orbit the planet. Two are part of the inner moons, orbiting in the prograde or with the planet's rotational direction. This pair of moons take less than a year to orbit Jupiter.

The Odd One Out

Of course, the star of the discovery, presented during the International Astronomical Union on Tuesday, July 17, is the so-called oddball planet. This runt is Jupiter's smallest known moon with a diameter of only 1 kilometer or a little over half a mile.

It orbits in the prograde and takes about a year and a half to circle Jupiter, but it doesn't behave quite like the rest of the group. The oddball is farther and more inclined than the other prograde moons, and its journey takes it through the orbits of the retrograde moons. This strange orbit makes it prone to collisions with the retrograde moons that are moving in the opposite direction.

"This is an unstable situation," Scott Sheppard of Carnegie says in a statement. "Head-on collisions would quickly break apart and grind the objects down to dust."

In fact, scientists suggest that this tiny moon could be the final remnant of a bigger oddball prograde moon that has been ground down to a smaller size after previous collisions. This hypothetical large prograde moon may also have formed some retrograde moon groupings.

The oddball moon is named Valetudo, after the great-granddaughter of the Roman god Jupiter.

Led by Sheppard, a team of scientists were looking at the outer fringes of the solar system for distant objects, and the gigantic planet was simply in their line of sight.

"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," Sheppard says.

According to Wired, astronomers have already searched this region of Jupiter before, but their instrument DECam was able to detect smaller, darker objects that are easy to miss using older equipment.</s>What just happened? In their hunt for Planet Nine, a proposed planet that may lie beyond Pluto, astronomers at the Carnegie Institution for Science discovered 12 moons orbiting Jupiter. The find pushes Jupiter’s total moon count to 79, the most of any planet in our solar system.

Scott S. 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 discovery actually took place in the spring of 2017 but as Gareth Williams at the International Astronomical Union’s Minor Planet Center points out, it takes several observations to confirm an object actually orbits Jupiter. That meant the entire process took a full year.

Nine of the new moons have retrograde orbits meaning they orbit in the opposite direction of Jupiter’s spin. They are thought to be the remnants of larger parent bodies that broke apart as a result of a collision with other bodies like asteroids, comets or other moons.

Two of the new moons are part of an inner group of moons closer to Jupiter that orbit in prograde, or the same direction as the planet’s rotation. Like the others, they, too, are thought to be fragments of a larger moon that slammed into something else.

The final discovery is classified as an “oddball” as it has an orbit unlike any other Jovian moon. It’s small – less than one kilometer in diameter – with a prograde orbit that crosses the outer retrograde moons. Because it’s moving in the opposite direction of the other moons, a head-on collision is much more likely. Such a collision would quickly break apart and grind the object down to dust, Sheppard said.</s>Jupiter got 12 new moons on Tuesday, July 17. Well, not exactly. Those dozen moons have, of course, always been in Jupiter’s orbit, but it was only this week that researchers from the Carnegie Institution for Science announced their discovery. The addition of these 12 brings the total number of moons (that we know of) to a whopping 79. As you might imagine, that’s far more than any other planet in our solar system can boast.

While the research team has suspected the existence of these 12 moons for about a year, it takes several observations in order to confirm that an object is, in fact, orbiting Jupiter. As such, the team took their time in confirming the new Jovian moons.

Scientists made their latest discovery when they were actually looking for another extraterrestrial body — Planet X, the planet that is suspected to exist somewhere beyond Pluto.

“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,” team leader Scott S. Sheppard said in an announcement. Of the 12 new moons discovered, 11 are described as normal moons, while the other is an “oddball.”

What makes it weird? Apparently, it’s just 1 kilometer wide, which means it’s the smallest moon scientists have discovered to date orbiting the planet, and it takes a full year and a half to make a complete trip around Jupiter. Moreover, its orbit crosses that of other moons in retrograde (those that travel in the opposite direction of Jupiter’s rotation), which is to say that at some point, multiple moons could collide. “This is an unstable situation,” Sheppard noted. “Head-on collisions would quickly break apart and grind the objects down to dust.”

This discovery could actually give scientists clues into the formation of moons and planets as a whole. As the team noted in its announcement, “Elucidating the complex influences that shaped a moon’s orbital history can teach scientists about our Solar System’s early years.” In this case, determining that there are still several small moons surrounding Jupiter suggests that they were actually created after the planets were formed.</s>Jupiter has had its share of visitors. The Pioneer 10 and 11 spacecraft, as well as Voyagers 1 and 2, flew by the gas giant in the 1970s. Ulysses, Cassini, and New Horizons all passed by the planet for gravity assists to get to their ultimate destinations. The Galileo probe orbited Jupiter from 1995 to 2003, and Juno has been there since 2016.



It may come as a surprise, then, that astronomers still find new moons orbiting the largest planet in the solar system. But 12 more moons were just discovered, bringing the total to 79, the most of any planet that orbits the sun. These small moons were not discovered by a spacecraft, but rather by powerful telescopes on Earth—and by a team, led by Carnegie Institution for Science astronomer Scott Sheppard, that didn't even set out to look for them.

"These moons are the last remnants of the objects that the planets were built from," Sheppard tells Popular Mechanics via email. "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."

11 New Moons and an Oddball

Two of the new moons were actually announced last year, but all of them were spotted at roughly the same time around 2017.

"It takes several observations to confirm an object actually orbits around Jupiter, so the whole process took a year," says Gareth Williams of the International Astronomical Union Minor Planet Center, who calculated the orbits of the new moons, in a press release.

The majority of the new moons, which range from about one to three kilometers in diameter (0.6 to 1.8 miles), were initially discovered with the Blanco 4-meter telescope in Chile. Additional telescopes in Chile, Arizona, and Hawaii were used to confirm their existence and determine their orbits.

The new moons orbit in two separate groups. Two of the small satellites were found orbiting in the "prograde group," a collection of moons that hang out just outside the four large Galilean moons (Io, Europa, Ganymede, and Callisto). The moons are so named because they orbit in prograde, or the same direction that Jupiter spins on its axis, completing an orbit in a little less than a year. The 10 remaining moons orbit in the farther-out "retrograde group"—a group of moons that orbit in the opposite direction of Jupiter's rotation, circling the planet about every two years.

There is one mysterious moon among the retrograde group that goes against the tide, traveling in the prograde direction. This oddball—nicknamed Valetudo for the Roman goddess of health and hygiene, one of Jupiter's great-granddaughters—is possibly Jupiter's smallest moon, less than a kilometer in diameter. It is thought to be the last surviving remnant of a larger moon that broke apart during a series of collisions as the planetary system was forming.

"There appear to be groups of moons with very similar orbital properties, which suggests there were once bigger moons that broke apart and we are now seeing the fragments of once bigger moons," Sheppard says. "We think there were originally three retrograde moons each around 100 km in size, but each of these parent moons were broken apart by collisions in the past with something."



That something could have been Valetudo—or the former large moon that it came from.

"We believe the oddball moon, which we are calling Valetudo, was captured in the opposite direction than the retrograde moons," Sheppard says. "Valetudo is like driving down the highway on the wrong side of the road. ... Valetudo likely has collided with some of the retrograde moons in the past, and what we see today is the last remnant of a once much larger moon that has now been ground to dust."

While the original, larger Valetudo was smashed in violent collisions, the smaller remnant that exists today is probably safe—for now. "Valetudo... is likely to collide with a retrograde object head-on every billion years or so," Sheppard says, which means it could have happened multiple times in the 4.5-billion-year history of the solar system, but is highly unlikely to occur again anytime soon.

The two small moons discovered in the prograde group also likely came from a common original body that was destroyed in collisions. It just goes to show how chaotic and violent planetary formation can be.

Sheppard and his team were not even searching for Jovian moons at first, but hunting for a hypothetical giant planet in the distant realms often called Planet Nine or Planet X. In 2014, Sheppard's team announced the discovery of the celestial body with the most distant known perihelion, or closest approach to the sun. The likely dwarf planet 2012 VP "never gets closer to the sun than 80 AU [Astronomical Units]," he says.

While looking for these extremely distant objects, Jupiter happened to wander into the team's field of view. "We knew Jupiter was near our observations for distant planets and dwarf planets that are beyond Pluto, so we specifically designed our observations to be able to search for new moons of Jupiter while also searching for much more distant solar system objects," Sheppard says.

Fortuitously, the same technique for finding far-flung objects orbiting the sun works to search for small objects orbiting Jupiter. "Both surveys take two images of the same sky location separated by a few hours," Sheppard says. "We then look for objects that have moved between the two images." While distant stars will not move in a few hours, objects beyond Pluto and moons orbiting Jupiter will.



Seventy-nine is an impressive number of Jovian moons, but Sheppard says there are likely more waiting to be discovered. "We think there are some 100 moons larger than 1 km around Jupiter... so a few more left to find."</s>(CN) — After a year of peering deep into the outer edge of space, Carnegie scientists have discovered 12 new moons orbiting Jupiter.

Carnegie Science researchers first spotted the newly discovered moons in the spring of 2017 as they searched for objects at the edge of the solar system, far beyond Pluto.

“Jupiter just happened to be in the sky near the search fields … 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,” Carnegie team leader Scott S. Sheppard said.

Jupiter has at least 79 moons orbiting it — the most of any planet in the solar system.

Scientists said the group of moons includes one “oddball” moon that is more distant than the others and has an orbit that crosses nine other, outer retrograde moons.

Retrograde moons orbit in the opposite direction of their parent planets. Prograde moons orbit in the same direction.

Sheppard said retrograde moons are “captured moons,” captured by Jupiter’s gravity as they approached it from the opposite direction and became retrograde in their orbits. If an object approaches Jupiter from behind, it is captured as a prograde and will orbit Jupiter in the same direction as it rotates.

The fact that the smallest moons in Jupiter’s orbital groups are abundant suggests the collisions that created them occurred after the era of planet formation, when a rotating disc of gas and dust surrounded the Sun.

This is important research, Sheppard said, because the influences that shape a moon’s orbital history provide information about our solar system’s early years.

He said a moon’s retrograde orbital direction means it’s likely to have a head-on collision with nearby prograde moons.

“This is an unstable situation,” Sheppard said. “Collisions would quickly break apart and grind the objects down to dust.”

This tendency to collide may be what caused orbital moon groupings that were formed eons years ago, Sheppard said.

Jupiter’s distant retrograde moons could be the remnants of three parent systems that broke apart during collisions with asteroids, comets or other moons, Sheppard said. The newly discovered retrograde moons take about two years to orbit Jupiter.

The name “Valetudo” has been proposed for the new oddball moon, Sheppard said. Valetudo was the Roman god Jupiter’s great-granddaughter, who was the goddess of health and hygiene.

Valetudo is a small moon, less than 1 kilometer in diameter.

Sheppard’s team in 2014 discovered Planet X — the object that is the farthest away in our solar system, even beyond Pluto.

Carnegie Science teams used the Blanco 4-meter telescope at Cerro Tololo Inter-American in Chile — one of the largest telescopes in the world — in their work to find the 11 new moons of Jupiter.

The discovery took “a lot of hard work,” Sheppard said. “It took over one year of constant observations to determine that these 12 objects were moons of Jupiter.”</s>A dozen new moons have been discovered orbiting Jupiter.

The new finding brings the total number of moons around the gas giant to a whopping 79 – the most of any planet in the solar system.

Astronomers accidentally spotted the tiny satellites while searching for a possible massive planet beyond Pluto.

They said the space rocks were created when three larger bodies that once orbited the planet were obliterated into smaller chunks by collisions with asteroids.

The researchers, from the Carnegie Institution for Science in Washington, DC, picked out one of the 12 moons as an 'oddball'.

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.

Team leader Dr Scott Sheppard said: 'It's a real oddball. It has an orbit like no other known Jovian moon. It is also likely Jupiter's smallest known moon, being less than one kilometre [0.6 miles] in diameter.'

The chance find brings the gas giant's tally of moons to 79 – 17 more than Saturn, which is the planet with the second most orbiting moons in the solar system.

All less than two miles (3.2km) wide, the moons are all very small, which is why they have only now been identified thanks to the team's modern, sensitive telescopes.

Eleven are 'normal' moons, with nine of them part of a distant outer swarm that orbit in the retrograde, meaning they move in the opposite direction to Jupiter's spin.

They are thought to be the remnants of three once larger moons that broke apart during collisions with asteroids, comets or other moons.

They take about two years to orbit Jupiter, which is the largest planet in the solar system.

The remaining two satellites others are among a closer, inner group that orbit in the prograde, or same direction.

They are also believed to be fragments of a larger moon that was broken apart and take just under a year to circle Jupiter.

It's further away than the prograde moons, taking around one and a half years to orbit around the planet.

This means, unlike those closer to Jupiter, it crosses the outer retrograde moons.

As a result, head on collisions are much more likely to occur between this 'oddball' prograde moon and its retrograde cousins moving in opposite directions.

Dr Sheppard said: 'This is an unstable situation. Head-on collisions would quickly break apart and grind the objects down to dust.'

It is possible the various orbital moon groupings we see today were formed in the distant past through this exact mechanism.

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.

The name Valetudo has been proposed for it, after the Roman god Jupiter's great-granddaughter, the goddess of health and hygiene.

The initial discovery of most of the new moons were made on the Blanco 4-meter telescope at Cerro Tololo Inter-American in Chile and operated by the National Optical Astronomical Observatory of the United States.

Several other telescopes were used to confirm the finds, including the 6.5-meter Magellan telescope at Carnegie's Las Campanas Observatory, also in Chile.

Elucidating the complex influences that shaped a moon's orbital history can teach scientists about our solar system's early years.

For example, the discovery that the smallest moons in Jupiter's various orbital groups are still abundant suggests the collisions that created them occurred after the era of planet formation.

This was at a time when the Sun was still surrounded by a rotating disc of gas and dust from which the planets were born.

Due to their sizes - just 0.6 to 1.9 miles (1 to 3km) in diameter - these moons are more influenced by surrounding gas and dust.

If these raw materials had still been present when Jupiter's first moons collided to form its current clusters, the drag exerted on the smaller ones would have made them spiral inwards. So they were likely formed after they had dissipated.</s>Scientists have discovered twelve new moons orbiting Jupiter, bringing the total number of natural satellites circling around the king of planets to a whopping 79. The findings include 11 “normal” outer moons, and one that scientists call an “oddball.” Researchers, led by Scott S Sheppard from Carnegie Institution for Science in the US, first spotted the moons in last year while they were looking for a possible massive planet far beyond Pluto.

“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 Sheppard. “It takes several observations to confirm an object actually orbits around Jupiter. So, the whole process took a year,” said Gareth Williams from the International Astronomical Union.

Nine of the new moons are part of a distant outer swarm of moons that orbit it in the retrograde, or opposite direction of Jupiter’s spin rotation. These distant retrograde moons are grouped into at least three distinct orbital groupings and are thought to be the remnants of three once-larger parent bodies that broke apart during collisions with asteroids, comets, or other moons.

The newly discovered retrograde moons take about two years to orbit Jupiter. Two of the new discoveries are part of a closer, inner group of moons that orbit in the prograde, or same direction as the planet’s rotation. These inner prograde moons all have similar orbital distances and angles of inclinations around Jupiter and so are thought to also be fragments of a larger moon that was broken apart.

These two newly discovered moons take a little less than a year to travel around Jupiter. “Our other discovery is a real oddball and has an orbit like no other known Jovian moon. It’s also likely Jupiter’s smallest known moon, being less than one kilometer in diameter,” Sheppard explained. This new “oddball” moon is more distant and more inclined than the prograde group of moons and takes about one and a half years to orbit Jupiter.

So, unlike the closer-in prograde group of moons, this new oddball prograde moon has an orbit that crosses the outer retrograde moons. As a result, head-on collisions are much more likely to occur between the “oddball” prograde and the retrograde moons, which are moving in opposite directions. “This is an unstable situation. Head-on collisions would quickly break apart and grind the objects down to dust,” said Sheppard.

It’s possible the various orbital moon groupings we see today were formed in the distant past through this exact mechanism. The team think this small “oddball” prograde moon could be the last-remaining remnant of a once-larger prograde-orbiting moon that formed some of the retrograde moon groupings during past head-on collisions. The name Valetudo has been proposed for it, after the Roman god Jupiter’s great-granddaughter, the goddess of health and hygiene.
Ten new moons are discovered around Jupiter, raising the count to 79 confirmed moons. One of these new moons, S/2016 J 2, nicknamed Valetudo, is notable for orbiting backwards compared to the other moons in its vicinity, and may collide with one of them in the future.