# Is Planet Nine shepherding the Kuiper Belt?

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Is it possible Planet Nine is shepherding the Kuiper Belt similar to the way Jupiter shepherds the asteroid belt?

I understand that very little is actually known about Planet Nine at this point, but has it been postulated that it has control over the Kuiper Belt? I don't exactly intend to read any theoretical papers on the existence of Planet Nine because I am sure it will be way over my head, but I understand that it is from the position of several Trans-Neptunian objects that its existence has any merit at all. So, I am wondering if part of that theory includes the Kuiper belt as a whole?

Estimates of Planet 9's orbit currently suggest that it doesn't have any major effect on the Kuiper Belt, because its orbit is too far away and on a different plane than the Kuiper belt, and from the inner Oort cloud, at 200 and 1200 aphelion and perihelion, However it does have an effect on Trans-Neptunian objects that transit through the Kuiper belt. It doesn't get closer than 4 times the distance of Pluto and it transits at a different plane to the Kuiper belt.

Shepherding is the act of actually creating and directing the asteroid belt by providing many objects with a semi stable orbit with too violent collisions to make a planet (biggest is Ceres at $${ m 500 km}$$ diameter), and having a massive effect on the unstable collection of asteroids, like making large stable groups around Jupiter's Lagrangian points at 60 degrees to Jupiter, and making fast resonant orbits that are not round like stable asteroids but periodically go close to Jupiter and then go straight through the inner asteroid belt and back to towards Jupiter actually in a triangle.

Neptune's orbit averages 30AU, and the Kuiper belt is generally held to be between Neptune and Pluto's orbits, Pluto orbits at 31-48AU.

In that sense, Pluto and Neptune are the two objects which have the biggest effect on the Kuiper belt.

The Trans-Neptunian objects all traverse the Kuiper belt, with their Perihelions ranging from 17 to 50 AU, and if Trans-Neptunian objects swing out towards Planet 9, it's a less stable orbit for them, than if they swing out away from planet 9, so all the large Kuiper belt objects swing away from the alledged direction of planet 9, where they can have a stable course without a transiting planet to interfere with them. Trans Neptunians tend to not align themselves with Planet 9's orbit and tend to find a balance away from Planet 9 and away from Jupiter and the majority of them don't get closer than Neptune, about 7/8ths of them are further than Neptune. https://en.wikipedia.org/wiki/List_of_trans-Neptunian_objects

The Trans-Neptunian objects are often referred to as Kuiper belt objects, and they didn't start their course to 100ds of AU's distance because of Planet 9, but now they are affected by planet 9 because they are in its vicinity over millions of years. In a million years, they have about 500 chances to approach planet 9, and 500,000 chances in a billion years.

The shepherding effect is complex, Jupiter accelerates objects very fast in stable orbits that resonate with it, it prevents planets from forming from the asteroid belt, and it disrupts the otherwise stable asteroid belt, sending objects fast through the asteroid belt and wherever, towards and away from the Sun. Jupiter created and maintains the asteroid belt which is unstable space debris, and it protects Earth from comets that want orbits that through its path.

Planet 9's inclination is about 30 degrees, so it can't interact with the inner Oort cloud, and the outer Oort cloud is too far away.

## Mystery Orbits in Outermost Reaches of Solar System not Caused by ‘Planet Nine’

The strange orbits of some objects in the farthest reaches of our solar system, hypothesized by some astronomers to be perturbed by an unknown planet (Planet 9), can instead be explained by the combined gravitational force of small objects in the Kuiper Belt orbiting the Sun beyond Neptune. (Image: movie poster from the film &lsquoPlan 9 From Outer Space&rsquo released in 1959 by Distributors Corporation of America).

What does this poster have to do with the story? Absolutely nothing. But if you get a chance to see this film, do so. Then you can proudly tell your friends that you watched what some movie critics claim is &ldquothe worst film in the history of cinema.&rdquo This movie is so bad on so many levels (and so cheaply made) that it is actually entertaining.

Mystery Orbits in Outermost Reaches of Solar System not Caused by &lsquoPlanet Nine&rsquo

The strange orbits of some objects in the farthest reaches of our solar system, hypothesized by some astronomers to be perturbed by an unknown planet (Planet 9), can instead be explained by the combined gravitational force of small objects in the Kuiper Belt orbiting the Sun beyond Neptune, say researchers.

The alternative explanation to the so-called &lsquoPlanet Nine&rsquo hypothesis, put forward by researchers at the University of Cambridge and the American University of Beirut, proposes a disc made up of small icy bodies with a combined mass as much as ten times that of Earth. When combined with a simplified model of the solar system, the gravitational forces of the hypothesized disc can account for the unusual orbital architecture exhibited by some objects at the outer reaches of the solar system.

While the new theory is not the first to propose that the gravitational forces of a massive disc made of small objects could avoid the need for a ninth planet, it is the first such theory which is able to explain the significant features of the observed orbits while accounting for the mass and gravity of the other eight planets in our solar system.

Beyond the orbit of Neptune lies the Kuiper Belt, which is made up of small bodies left over from the formation of the solar system. Neptune and the other giant planets gravitationally influence the objects in the Kuiper Belt and beyond, collectively known as trans-Neptunian Objects (TNOs), which encircle the Sun on nearly-circular paths from almost all directions.

However, astronomers have discovered some mysterious outliers. Since 2003, around 30 TNOs on highly elliptical orbits have been spotted. They stand out from the rest of the TNOs by sharing, on average, the same spatial orientation. This type of clustering cannot be explained by our existing eight-planet solar system architecture and has led to some astronomers hypothesizing that the unusual orbits could be influenced by the existence of an as-yet-unknown ninth planet.

The &lsquoPlanet Nine&rsquo hypothesis suggests that to account for the unusual orbits of these TNOs, there would have to be another planet, believed to be about ten times more massive than Earth, lurking in the distant reaches of the solar system and &lsquoshepherding&rsquo the TNOs in the same direction through the combined effect of its gravity and that of the rest of the solar system.

&ldquoThe Planet Nine hypothesis is a fascinating one, but if the hypothesized ninth planet exists, it has so far avoided detection,&rdquo said co-author Antranik Sefilian, a PhD student in Cambridge&rsquos Department of Applied Mathematics and Theoretical Physics. &ldquoWe wanted to see whether there could be another, less dramatic and perhaps more natural, cause for the unusual orbits we see in some TNOs. We thought, rather than allowing for a ninth planet, and then worry about its formation and unusual orbit, why not simply account for the gravity of small objects constituting a disc beyond the orbit of Neptune and see what it does for us?&rdquo

Professor Jihad Touma from the American University of Beirut and his former student Sefilian modeled the full spatial dynamics of TNOs with the combined action of the giant outer planets and a massive, extended disc beyond Neptune. The duo&rsquos calculations, which grew out of a seminar at the American University of Beirut, revealed that such a model can explain the perplexing spatially clustered orbits of some TNOs. In the process, they were able to identify ranges in the disc&rsquos mass, its &lsquoroundness&rsquo (or eccentricity), and forced gradual shifts in its orientations (or precession rate), which faithfully reproduced the outlier TNO orbits.

&ldquoIf you remove planet nine from the model and instead allow for lots of small objects scattered across a wide area, collective attractions between those objects could just as easily account for the eccentric orbits we see in some TNOs,&rdquo said Sefilian, who is a Gates Cambridge Scholar and a member of Darwin College.

Earlier attempts to estimate the total mass of objects beyond Neptune have only added up to around one-tenth the mass of the Earth. However, in order for the TNOs to have the observed orbits and for there to be no Planet Nine, the model put forward by Sefilian and Touma requires the combined mass of the Kuiper Belt to be between a few to ten times the mass of the Earth.

&ldquoWhen observing other systems, we often study the disc surrounding the host star to infer the properties of any planets in orbit around it,&rdquo said Sefilian. &ldquoThe problem is when you&rsquore observing the disc from inside the system, it&rsquos almost impossible to see the whole thing at once. While we don&rsquot have direct observational evidence for the disc, neither do we have it for Planet Nine, which is why we&rsquore investigating other possibilities. Nevertheless, it is interesting to note that observations of Kuiper belt analogues around other stars, as well as planet formation models, reveal massive remnant populations of debris.

&ldquoIt&rsquos also possible that both things could be true &ndash there could be a massive disc and a ninth planet. With the discovery of each new TNO, we gather more evidence that might help explain their behavior.&rdquo

## Is ‘Planet Nine’ Actually A Black Hole In The Solar System? There’s Only One Way To Find Out

Is there a “Planet Nine” lurking at the fringes of the solar system? Or could it be something a whole lot more scary—a primordial black hole?

A new paper by Harvard University undergraduate Amir Siraj and theoretical astrophysicist Avi Loeb suggests that a new telescope currently being constructed in Chile could hold the key to discovering whether there is, in fact, a black hole located in our own solar system.

That would be the find of the century, arguably way more fundamental than the discovery of any “Planet Nine.”

Published this week on arXiv is “Searching for Black Holes in the Outer Solar System with LSST,” in which Loeb and Siraj propose that the Rubin Observatory in the thin mountain air at the peak of Cerro Pachón in Chile’s Elqui Valley—whose exciting 10-year survey of the sky is due for “first light” in 2022—will be able to either rule out or confirm Planet Nine as a black hole within a year.

The Rubin Observatory under construction, as seen from inside the Gemini South Telescope dome, in . [+] July 2019.

### What and where is ‘Planet Nine?’

“Planet Nine” is speculated to be a super-Earth—a planet about five to 15 times larger than Earth—that was first theorized in 2016. Its existence would explain why objects in the Kuiper Belt—a doughnut-shaped region of the outer solar system beyond the orbit of Neptune, and home to Pluto—are clustered and aligned in a particular way. If there is an as-yet-undetected planet in the Kuiper Belt, it’s cold, dark, and way too small to see.

“Planet Nine” is considered unlikely to exist because it would be difficult for the solar system to collect enough material at such a distance from the Sun to form a super-Earth-sized planet. Which has led astronomers to think-up some even crazier-sounding theories about what, exactly, the observed “Planet Nine effect” could actually be.

One of the theories is that it is that there is a primordial black hole in our solar system. Gulp.

### Why do some think that Planet Nine could be a black hole?

“If it exists and is not a statistical fluke, ‘Planet Nine’ is most likely a planet, not a black hole,” said lead author Siraj in an email to me last week. “There is no unambiguous evidence showing that black holes exist that are less massive than the about mass of the Sun.”

However, another recent paper showed that the probability of the solar system capturing a free-floating planet at the distance of Planet Nine could be comparable to the probability of gravitationally capturing a black hole with a similar mass.

To be clear, it probably isn’t a black hole. “No primordial black holes have been unambiguously detected, and it is unclear exactly how they would form,” says Siraj, but he thinks it’s worth checking out. “Because of the incredibly exciting implications of a black hole potentially hiding in the solar system, it is worth checking to rule it out,” says Siraj. “Or perhaps to confirm it.”

### How to find Planet Nine or a black hole

The first, very expensive, way to find a black hole in the solar system would be to send 100 specially-equipped spacecraft, as proposed by Edward Written, and Scott Lawrence and Zeeve Rogoszinski at the University of Maryland, to search a vast area of space. Those spacecraft’s high-precision atomic clocks would reveal its presence as they passed through the gravitational field of any “Planet Nine” or black hole, the tell-tale sign being that they would speed up.

However, a recent paper by Loeb showed that drag and magnetic noise from the interstellar medium would likely dominate over any gravitational signal from “Planet Nine.”

“So we need another way to figure out if Planet Nine is a black hole or not, and that was the motivation for my paper,” says Siraj. Siraj and Loeb’s paper focuses on the search for the occasional flares of light that would naturally occur from collisions between Oort cloud objects and the black hole, if it exists.

This illustration shows that the Kuiper Belt is shaped like a disk [see inset diagram] and resides . [+] within the shell-like structure of the Oort Cloud. Located on the outskirts of the solar system, the Kuiper Belt is a "junkyard" of countless icy bodies left over from the solar system's formation. The Oort Cloud is a vast shell of billions of comets. The inset diagram compares Pluto's orbit with a Kuiper Belt binary object called 1998 WW31. The Kuiper Belt [the fuzzy disk] extends from inside Pluto's orbit to the edge of the solar system

NASA/ESA and A. Feild (Space Telescope Science Institute)

### What is the Rubin Observatory?

The paper suggests that the Rubin Observatory—which is now in an advanced state of construction close to the Gemini South telescope—will be able to confirm the existence, or not, of a black hole in the solar system.

The Rubin Observatory is all about wide-angle, real-time astronomy. Its 10-year “Legacy Survey of Space and Time” (LSST) survey of the sky will image the entire southern hemisphere night sky every three nights, with each image covering an area 40 times the size of the full Moon.

By both alerting astronomers to real-time events and constructing a massive data archive, it’s expected to dramatically advance astronomers’ knowledge of the cosmos.

### How to find black hole in the solar system

“The LSST will be unique in its ability to survey the entire sky about twice per week at a remarkable level of sensitivity,” said Siraj. “We calculated that the flares from the accretion of a small body onto a ‘Planet Nine’ black hole would be brightest near the optical band, where LSST operates.”

That makes the Rubin Observatory ideal for confirming whether “Planet Nine” could be a black hole. “Since Planet Nine's position is unknown, the fact that LSST surveys the sky so quickly maximizes its chance of catching a flare.”

However, there is one small problem with hunting a black hole. SpaceX Starlink and other upcoming mega-constellations of satellites are said to be particularly problematic for the Rubin Observatory’s plans to survey the night sky.

### Could SpaceX Starlink and other mega-constellations jeopardize the search for a black hole?

“It certainly is possible for mega-constellations to harm such a search,” said Siraj. “They could be easily distinguished from a ‘Planet Nine black hole’ because of their large proper motions—resulting in streaks of light across the image, as opposed to a dot—but if a satellite happened to interfere with the line-of-sight to ‘Planet Nine’ at exactly the moment a flare was occurring, then that could prevent us from seeing the flare.”

## No Planet Nine? Weird Orbits of Distant Objects May Have Different Explanation

The weirdly clustered orbits of some far-flung bodies in our solar system can be explained without invoking a big, undiscovered "Planet Nine," a new study suggests.

The shepherding gravitational pull could come from many fellow trans-Neptunian objects (TNOs) rather than a single massive world, according to the research.

"If you remove Planet Nine from the model, and instead allow for lots of small objects scattered across a wide area, collective attractions between those objects could just as easily account for the eccentric orbits we see in some TNOs," study lead author Antranik Sefilian, a doctoral student in the Department of Applied Mathematics and Theoretical Physics at Cambridge University in England, said in a statement. [The Evidence for 'Planet Nine' in Our Solar System (Gallery)]

The hunt for Planet Nine &mdash or, as some prefer to call it, Planet X or Giant Planet Five &mdash began in earnest in 2014. That year, astronomers Chad Trujillo and Scott Sheppard proposed the existence of a large, unseen "perturber" beyond Neptune, whose gravitational influence could explain oddities in the orbits of distant objects like the dwarf planets Sedna and 2012 VP113.

In January 2016, Konstantin Batygin and Mike Brown contributed more evidence, announcing that other TNOs also appeared to bear this gravitational imprint. Batygin and Brown estimated that the perturber is perhaps 10 times more massive than Earth and lies about 600 astronomical units (AU) from the sun on average. (One AU is the Earth-sun distance &mdash about 93 million miles, or 150 million kilometers.)

The case has been building ever since, as astronomers have found more and more "clustered" TNOs the tally is up to about 30 at the moment.

But Planet Nine's existence isn't a slam dunk: Some astronomers think the orbit-shaping tug is more likely coming from many small bodies. The new study, which Sefilian conducted with Jihad Touma of the American University of Beirut, explores this latter scenario.

The duo's modeling work suggests that the strength-in-numbers explanation does indeed work &mdash if the mass of the Kuiper Belt, the ring of bodies beyond Neptune, is a few to 10 times that of Earth. This is a pretty big "if," given that most estimates peg the Kuiper Belt's mass at less than 10 percent that of Earth (and one recent study put the figure at 0.02 Earth masses).

But other solar systems are known to harbor massive disks of material in their outer reaches, Sefilian and Touma noted. And our failure to spot one around our own sun doesn't mean it doesn't exist, they stressed.

"The problem is, when you're observing the disk from inside the system, it's almost impossible to see the whole thing at once. While we don't have direct observational evidence for the disk, neither do we have it for Planet Nine, which is why we're investigating other possibilities," Sefilian said.

"It's also possible that both things could be true &mdash there could be a massive disk and a ninth planet," he added. "With the discovery of each new TNO, we gather more evidence that might help explain their behavior."

## The Best Guess at What 'Planet Nine' Looks Like

The astronomical community is abuzz with the possibility that a ninth planet exists in the far reaches of the solar system. A new study by European scientists imagines what this hypothetical planet might look like, revealing important insights as to how we might actually find it.

To quickly recap, astronomers haven’t actually proven the existence of Planet Nine, but its existence is inferred by the unlikely orbits of distant Kuiper belt objects . This data strongly suggests that something is way out there far beyond Pluto, leading scientists to wonder what it might look like and how we might ever be able to find it.

###### How Astronomers Are Going to Find Planet Nine

Ten years ago, billions of humans had their worldview upended when a group of astronomers announced

Astrophysicist Christoph Mordasini from the University of Bern and his PhD Student Esther Linder are planet modeling specialists, and they recently applied their expertise to the figuring out what Planet Nine might look like. Their ensuing analysis , which has been accepted by the science journal Astronomy & Astrophysics, paints a fascinating portrait of a dark and cold planet in the far reaches of the solar system.

The purpose of the exercise was to create ballpark estimates for the planet’s radius, temperature, brightness, and most importantly level of thermal radiation. The last item is of particular interest because while Planet Nine may be too dim to be seen with our current telescopes, it’s thermal signature might be detectable by other means. Encouragingly, the simulations created by Mordasini and Linder suggest this may very well be the case.

With very little data to go on, the researchers decided to simulate several different scenarios. For the study, the astrophysicists assumed that Planet Nine is a smaller version of Uranus and Neptune. They modeled hypothetical planets that were five, 10, 20 and 50 times heavier than Earth, and at distances of 280, 700, and 1,120 AU from the Sun (1 AU being the average distance of the Earth to the Sun for comparison, Pluto is about 40 AU from the Sun). One particular simulation jumped out at the researchers as plausible.

“For me candidate Planet Nine is a close object, although it is about 700 times further away as the distance between the Earth and the Sun,” noted Linder in a statement. The “ideal” Planet Nine, according to the models, features a mass ten times heavier than Earth, and a radius 3.7 times wider than our planet. Similar to Uranus and Neptune, it has an outer envelope of helium and hydrogen, a layer of gas (also consisting of helium and hydrogen), a water ice layer, a silicate mantle, and an iron core.

The models also projected a temperature of 47 Kelvin (-374 degrees Fahrenheit, -226 degrees Celsius). Planet Nine is bitterly cold—but this data suggests that it’s being heated from the inside.

“This means that the planet’s emission is dominated by the cooling of its core, otherwise the temperature would only be 10 Kelvin,” explained Linder.“Its intrinsic power is about 1,000 times bigger than its absorbed power.”

So, Planet Nine’s reflected sunlight contributes a very tiny part of the total radiation that could be detected on Earth (it’s exceptionally dim, less than 1 percent as bright as Jupiter). But it also means that this nominal planet is much brighter in the infrared than in the visual. As the researchers put it, Planet Nine is a “self-luminous planet.”

That’s good news for astronomers, who can now scan the heavens for these thermal signatures. All this is quite remarkable even though we’ve never actually seen this thing, it’s actually starting to take shape.

## Planet Nine: Astronomers Uncover Evidence for mini-Neptune in Outer Solar System

A team of astronomers at the California Institute of Technology has found strong evidence of a massive gaseous planet – informally named Planet Nine – tracing an extremely elongated orbit in the outer Solar System.

Planet Nine is thought to be gaseous, similar to Uranus and Neptune hypothetical lightning lights up the night side. Image credit: R. Hurt, IPAC / Caltech.

Planet Nine is likely a gas giant about 10 times more massive than Earth, according to the astronomers – Dr. Konstantin Batygin and Prof. Mike Brown, both of Caltech’s Division of Geological and Planetary Sciences.

The planet orbits 20 times farther from the Sun on average than does Neptune. It would take this gas giant approximately 15,000 years to make just one full orbit around the Sun.

The scientists discovered the planet’s existence through mathematical modeling and computer simulations but have not yet observed the object directly.

“This would be a real ninth planet. There have only been two true planets discovered since ancient times, and this would be a third. It’s a pretty substantial chunk of our Solar System that’s still out there to be found, which is pretty exciting,” Prof. Brown said.

“The planet is sufficiently large that there should be no debate about whether it is a true planet.”

Unlike the class of smaller objects now known as dwarf planets, Planet Nine gravitationally dominates its neighborhood of the Solar System.

In their study, Prof. Brown and Dr. Batygin realized that the six most distant known objects in the Solar System – 2007 TG422, 2013 RF98, 2004 VN112, 2012 VP113, 2012 GB174, and the minor planet 90377 Sedna – all follow elliptical orbits that point in the same direction in physical space. That is surprising because the outermost points of their orbits move around the Solar System, and they travel at different rates.

The six most distant known objects in the Solar System – 2007 TG422, 2013 RF98, 2004 VN112, 2012 VP113, 2012 GB174, and the minor planet 90377 Sedna – mysteriously line up in a single direction. Also, when viewed in three dimensions, they tilt nearly identically away from the plane of the Solar System. Image credit: R. Hurt, IPAC / Caltech.

“It’s almost like having six hands on a clock all moving at different rates, and when you happen to look up, they’re all in exactly the same place. The odds of having that happen are something like 1 in 100,” Prof. Brown said.

The orbits of these distant objects are also all tilted in the same way – pointing 30 degrees downward in the same direction relative to the plane of the eight known planets. The probability of that happening is about 0.007%.

The scientists describe their work in the Jan. 20 issue of the Astronomical Journal and show that a massive planet in a distant eccentric orbit anti-aligned with the other six objects is required to maintain this configuration.

“We find that the observed orbital alignment can be maintained by a distant eccentric planet with mass >10 Earth masses whose orbit lies in approximately the same plane as those of the distant Kuiper Belt objects, but whose perihelion is 180 degrees away from the perihelia of the minor bodies,” they explained.

“Although we were initially quite skeptical that this planet could exist, as we continued to investigate its orbit and what it would mean for the outer Solar System, we become increasingly convinced that it is out there,” Dr. Batygin said.

“For the first time in over 150 years, there is solid evidence that the Solar System’s planetary census is incomplete.”

Konstantin Batygin & Michael E. Brown. 2016. Evidence for a Distant Giant Planet in the Solar System. Astronomical Journal 151, 22 doi: 10.3847/0004-6256/151/2/22

## NASA Says Mysterious Nearby Exoplanet May Help Find Planet Nine

It’s not every day that NASA uses the term “Planet Nine” in a press release, so when it did in a recent one about new Hubble telescope observations of a massive exoplanet orbiting a nearby young binary star system, it garnered a lot of attention from Planet Nine proponents. Why is NASA interested in HD 106906 b and why have they linked it with the potential existence of Planet Nine in our solar system?

“This system draws a potentially unique comparison with our solar system. It’s very widely separated from its host stars on an eccentric and highly misaligned orbit, just like the prediction for Planet Nine. This begs the question of how these planets formed and evolved to end up in their current configuration.”

Meiji Nguyen of the University of California, Berkeley, is the lead author of a paper in The Astronomical Journal describing the strange orbit of HD 106906 b, an exoplanet 11 times the size of Jupiter orbiting binary stars a mere 336 light years from Earth. Discovered in 2013 by astronomers using the Magellan Telescopes in Chile, its orbit was unknown until the more powerful Hubble telescope picked it up. The HD 106906 binary system is only 15 million years old – a newborn when compared to 4.5 billion-year age of our solar system. That means whatever happened to put HD 106906 b in its current weird and far-flung orbit happened recently. Could the same thing have happened to our own rumored Planet Nine shortly after its birth?

The 11-Jupiter-mass exoplanet called HD 106906 b is shown in this artist’s illustration. Credits: NASA, ESA, and M. Kornmesser (ESA/Hubble)

“The prevailing theory is that it formed much closer to its stars, about three times the distance that Earth is from the Sun. But drag within the system’s gas disk caused the planet’s orbit to decay, forcing it to migrate inward toward its stellar pair. The gravitational effects from the whirling twin stars then kicked it out onto an eccentric orbit that almost threw it out of the system and into the void of interstellar space. Then a passing star from outside the system stabilized the exoplanet’s orbit and prevented it from leaving its home system.”

Paul Kalas, another Berkeley professor and co-author, explains in the university’s press release how HD 106906 b started out in a tight orbit around its two stars before being flung like an Olympic hammer throw on a path that would take it out of the system completely. However, a passing star’s gravity caught it and pushed it back into a new orbit more than 730 times the distance of Earth from the Sun. In addition, this new extreme orbit is misaligned, elongated and external to the debris disk of the twin host stars – a disk similar to our own solar system’s Kuiper Belt. That disk itself is distorted, which helped the team define HD 106906 b’s orbit.

This graphic shows how the exoplanet HD 106906 b may have evolved over time, arriving at its current, widely separated, eccentric and highly misaligned orbit. (Graphic courtesy of NASA, ESA, and L. Hustak/STScI)

“The idea is that every time the planet comes to its closest approach to the binary star, it stirs up the material in the disk. So, every time the planet comes through, it truncates the disk and pushes it up on one side. This scenario has been tested with simulations of this system with the planet on a similar orbit — this was before we knew what the orbit of the planet was.”

Team member Robert De Rosa describes why this phenomena made the astronomers think of Planet Nine – not only do some scientists believe it was violently kicked out of a close solar orbit early in its life and saved by a passing star, this could explain the strange clusterings of space rocks in the Kuiper Belt.

“What I really think makes HD 106906 unique is that it is the only exoplanet that we know that is directly imaged, surrounded by a debris disk, misaligned relative to its system and is widely separated. This is what makes it the sole candidate we have found thus far whose orbit is analogous to the hypothetical Planet Nine.”

Meiji Nguyen says HD 106906 b is real and makes the connection to Planet Nine. As we’re finding so often when it comes to new discoveries in astronomy – if there’s one, there’s more. Knowing how HD 106906 b came into existence and moved to its current eccentric location and orbit gives astronomers a better roadmap to proving the existence of Planet Nine and finding it. NASA scientists are already planning to use the James Webb Space Telescope, scheduled to be launched in 2021, to further observe HD 106906 b and also look for other similar oddball exoplanets.

## “More Mystery” –Planet 9 May Actually Be a Gargantuan Disk

It’s possible that there could be a massive disc and a ninth planet, said Antranik Sefilian at Cambridge’s Department of Applied Mathematics and Theoretical Physics. “With the discovery of each new trans-Neptunian Object (TNO), we gather more evidence that might help explain their behavior.”

“The Planet Nine hypothesis is a fascinating one, but if the hypothesized ninth planet exists, it has so far avoided detection,” said co-author Sefilian. “We wanted to see whether there could be another, less dramatic and perhaps more natural, cause for the unusual orbits we see in some TNOs. We thought, rather than allowing for a ninth planet, and then worry about its formation and unusual orbit, why not simply account for the gravity of small objects constituting a disc beyond the orbit of Neptune and see what it does for us?”

The strange orbits of some objects in the farthest reaches of our solar system, hypothesized by some astronomers to be shaped by an unknown ninth planet, can instead be explained by the combined gravitational force of small objects orbiting the Sun beyond Neptune, say researchers.

The alternative explanation to the so-called ‘Planet Nine’ hypothesis, put forward by researchers at the University of Cambridge and the American University of Beirut, proposes a disc made up of small icy bodies with a combined mass as much as ten times that of Earth. When combined with a simplified model of the solar system, the gravitational forces of the hypothesized disc can account for the unusual orbital architecture exhibited by some objects at the outer reaches of the solar system.

While the new theory is not the first to propose that the gravitational forces of a massive disc made of small objects could avoid the need for a ninth planet, it is the first such theory which is able to explain the significant features of the observed orbits while accounting for the mass and gravity of the other eight planets in our solar system. The results are reported in the Astronomical Journal.

Beyond the orbit of Neptune lies the Kuiper Belt, which is made up of small bodies left over from the formation of the solar system. Neptune and the other giant planets gravitationally influence the objects in the Kuiper Belt and beyond, collectively known as trans-Neptunian Objects (TNOs), which encircle the Sun on nearly-circular paths from almost all directions.

However, astronomers have discovered some mysterious outliers. Since 2003, around 30 TNOs on highly elliptical orbits have been spotted: they stand out from the rest of the TNOs by sharing, on average, the same spatial orientation. This type of clustering cannot be explained by our existing eight-planet solar system architecture and has led to some astronomers hypothesising that the unusual orbits could be influenced by the existence of an as-yet-unknown ninth planet.

The ‘Planet Nine’ hypothesis suggests that to account for the unusual orbits of these TNOs, there would have to be another planet, believed to be about ten times more massive than Earth, lurking in the distant reaches of the solar system and ‘shepherding’ the TNOs in the same direction through the combined effect of its gravity and that of the rest of the solar system.

Professor Jihad Touma, from the American University of Beirut, and his former student Sefilian modelled the full spatial dynamics of TNOs with the combined action of the giant outer planets and a massive, extended disc beyond Neptune. The duo’s calculations, which grew out of a seminar at the American University of Beirut, revealed that such a model can explain the perplexing spatially clustered orbits of some TNOs. In the process, they were able to identify ranges in the disc’s mass, its ‘roundness’ (or eccentricity), and forced gradual shifts in its orientations (or precession rate), which faithfully reproduced the outlier TNO orbits.

“If you remove planet nine from the model and instead allow for lots of small objects scattered across a wide area, collective attractions between those objects could just as easily account for the eccentric orbits we see in some TNOs,” said Sefilian, who is a Gates Cambridge Scholar and a member of Darwin College.

Earlier attempts to estimate the total mass of objects beyond Neptune have only added up to around one-tenth the mass of the Earth. However, in order for the TNOs to have the observed orbits and for there to be no Planet Nine, the model put forward by Sefilian and Touma requires the combined mass of the Kuiper Belt to be between a few to ten times the mass of the Earth.

“When observing other systems, we often study the disc surrounding the host star to infer the properties of any planets in orbit around it,” said Sefilian. “The problem is when you’re observing the disc from inside the system, it’s almost impossible to see the whole thing at once. While we don’t have direct observational evidence for the disc, neither do we have it for Planet Nine, which is why we’re investigating other possibilities. Nevertheless, it is interesting to note that observations of Kuiper belt analogues around other stars, as well as planet formation models, reveal massive remnant populations of debris.

Antranik A. Sefilian and Jihad R. Touma. ‘Shepherding in a self-gravitating disk of trans-Neptunian objects.’ Astronomical Journal (2019).

## Is Planet Nine shepherding the Kuiper Belt? - Astronomy

Caltech researchers have found evidence of a giant planet tracing a bizarre, highly elongated orbit in the outer solar system. The object, which the researchers have nicknamed Planet Nine, has a mass about 10 times that of Earth and orbits about 20 times farther from the sun on average than does Neptune (which orbits the sun at an average distance of 2.8 billion miles). In fact, it would take this new planet between 10,000 and 20,000 years to make just one full orbit around the sun.

The researchers, Konstantin Batygin and Mike Brown, discovered the planet's existence through mathematical modeling and computer simulations but have not yet observed the object directly.

"This would be a real ninth planet," says Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy. "There have only been two true planets discovered since ancient times, and this would be a third. It's a pretty substantial chunk of our solar system that's still out there to be found, which is pretty exciting."

Brown notes that the putative ninth planet--at 5,000 times the mass of Pluto--is sufficiently large that there should be no debate about whether it is a true planet. Unlike the class of smaller objects now known as dwarf planets, Planet Nine gravitationally dominates its neighborhood of the solar system. In fact, it dominates a region larger than any of the other known planets--a fact that Brown says makes it "the most planet-y of the planets in the whole solar system."

Batygin and Brown describe their work in the current issue of the Astronomical Journal and show how Planet Nine helps explain a number of mysterious features of the field of icy objects and debris beyond Neptune known as the Kuiper Belt.

"Although we were initially quite skeptical that this planet could exist, as we continued to investigate its orbit and what it would mean for the outer solar system, we become increasingly convinced that it is out there," says Batygin, an assistant professor of planetary science. "For the first time in over 150 years, there is solid evidence that the solar system's planetary census is incomplete."

The road to the theoretical discovery was not straightforward. In 2014, a former postdoc of Brown's, Chad Trujillo, and his colleague Scott Shepherd published a paper noting that 13 of the most distant objects in the Kuiper Belt are similar with respect to an obscure orbital feature. To explain that similarity, they suggested the possible presence of a small planet. Brown thought the planet solution was unlikely, but his interest was piqued.

He took the problem down the hall to Batygin, and the two started what became a year-and-a-half-long collaboration to investigate the distant objects. As an observer and a theorist, respectively, the researchers approached the work from very different perspectives--Brown as someone who looks at the sky and tries to anchor everything in the context of what can be seen, and Batygin as someone who puts himself within the context of dynamics, considering how things might work from a physics standpoint. Those differences allowed the researchers to challenge each other's ideas and to consider new possibilities. "I would bring in some of these observational aspects he would come back with arguments from theory, and we would push each other. I don't think the discovery would have happened without that back and forth," says Brown. " It was perhaps the most fun year of working on a problem in the solar system that I've ever had."

Fairly quickly Batygin and Brown realized that the six most distant objects from Trujillo and Shepherd's original collection all follow elliptical orbits that point in the same direction in physical space. That is particularly surprising because the outermost points of their orbits move around the solar system, and they travel at different rates.

"It's almost like having six hands on a clock all moving at different rates, and when you happen to look up, they're all in exactly the same place," says Brown. The odds of having that happen are something like 1 in 100, he says. But on top of that, the orbits of the six objects are also all tilted in the same way--pointing about 30 degrees downward in the same direction relative to the plane of the eight known planets. The probability of that happening is about 0.007 percent. "Basically it shouldn't happen randomly," Brown says. "So we thought something else must be shaping these orbits."

The first possibility they investigated was that perhaps there are enough distant Kuiper Belt objects--some of which have not yet been discovered--to exert the gravity needed to keep that subpopulation clustered together. The researchers quickly ruled this out when it turned out that such a scenario would require the Kuiper Belt to have about 100 times the mass it has today.

That left them with the idea of a planet. Their first instinct was to run simulations involving a planet in a distant orbit that encircled the orbits of the six Kuiper Belt objects, acting like a giant lasso to wrangle them into their alignment. Batygin says that almost works but does not provide the observed eccentricities precisely. "Close, but no cigar," he says.

Then, effectively by accident, Batygin and Brown noticed that if they ran their simulations with a massive planet in an anti-aligned orbit--an orbit in which the planet's closest approach to the sun, or perihelion, is 180 degrees across from the perihelion of all the other objects and known planets--the distant Kuiper Belt objects in the simulation assumed the alignment that is actually observed.

"Your natural response is 'This orbital geometry can't be right. This can't be stable over the long term because, after all, this would cause the planet and these objects to meet and eventually collide,'" says Batygin. But through a mechanism known as mean-motion resonance, the anti-aligned orbit of the ninth planet actually prevents the Kuiper Belt objects from colliding with it and keeps them aligned. As orbiting objects approach each other they exchange energy. So, for example, for every four orbits Planet Nine makes, a distant Kuiper Belt object might complete nine orbits. They never collide. Instead, like a parent maintaining the arc of a child on a swing with periodic pushes, Planet Nine nudges the orbits of distant Kuiper Belt objects such that their configuration with relation to the planet is preserved.

"Still, I was very skeptical," says Batygin. "I had never seen anything like this in celestial mechanics."

But little by little, as the researchers investigated additional features and consequences of the model, they became persuaded. "A good theory should not only explain things that you set out to explain. It should hopefully explain things that you didn't set out to explain and make predictions that are testable," says Batygin.

And indeed Planet Nine's existence helps explain more than just the alignment of the distant Kuiper Belt objects. It also provides an explanation for the mysterious orbits that two of them trace. The first of those objects, dubbed Sedna, was discovered by Brown in 2003. Unlike standard-variety Kuiper Belt objects, which get gravitationally "kicked out" by Neptune and then return back to it, Sedna never gets very close to Neptune. A second object like Sedna, known as 2012 VP113, was announced by Trujillo and Shepherd in 2014. Batygin and Brown found that the presence of Planet Nine in its proposed orbit naturally produces Sedna-like objects by taking a standard Kuiper Belt object and slowly pulling it away into an orbit less connected to Neptune.

But the real kicker for the researchers was the fact that their simulations also predicted that there would be objects in the Kuiper Belt on orbits inclined perpendicularly to the plane of the planets. Batygin kept finding evidence for these in his simulations and took them to Brown. "Suddenly I realized there are objects like that," recalls Brown. In the last three years, observers have identified four objects tracing orbits roughly along one perpendicular line from Neptune and one object along another. "We plotted up the positions of those objects and their orbits, and they matched the simulations exactly," says Brown. "When we found that, my jaw sort of hit the floor."

"When the simulation aligned the distant Kuiper Belt objects and created objects like Sedna, we thought this is kind of awesome--you kill two birds with one stone," says Batygin. "But with the existence of the planet also explaining these perpendicular orbits, not only do you kill two birds, you also take down a bird that you didn't realize was sitting in a nearby tree."

Where did Planet Nine come from and how did it end up in the outer solar system? Scientists have long believed that the early solar system began with four planetary cores that went on to grab all of the gas around them, forming the four gas planets--Jupiter, Saturn, Uranus, and Neptune. Over time, collisions and ejections shaped them and moved them out to their present locations. "But there is no reason that there could not have been five cores, rather than four," says Brown. Planet Nine could represent that fifth core, and if it got too close to Jupiter or Saturn, it could have been ejected into its distant, eccentric orbit.

Batygin and Brown continue to refine their simulations and learn more about the planet's orbit and its influence on the distant solar system. Meanwhile, Brown and other colleagues have begun searching the skies for Planet Nine. Only the planet's rough orbit is known, not the precise location of the planet on that elliptical path. If the planet happens to be close to its perihelion, Brown says, astronomers should be able to spot it in images captured by previous surveys. If it is in the most distant part of its orbit, the world's largest telescopes--such as the twin 10-meter telescopes at the W. M. Keck Observatory and the Subaru Telescope, all on Mauna Kea in Hawaii--will be needed to see it. If, however, Planet Nine is now located anywhere in between, many telescopes have a shot at finding it.

"I would love to find it," says Brown. "But I'd also be perfectly happy if someone else found it. That is why we're publishing this paper. We hope that other people are going to get inspired and start searching."

In terms of understanding more about the solar system's context in the rest of the universe, Batygin says that in a couple of ways, this ninth planet that seems like such an oddball to us would actually make our solar system more similar to the other planetary systems that astronomers are finding around other stars. First, most of the planets around other sunlike stars have no single orbital range--that is, some orbit extremely close to their host stars while others follow exceptionally distant orbits. Second, the most common planets around other stars range between 1 and 10 Earth-masses.

"One of the most startling discoveries about other planetary systems has been that the most common type of planet out there has a mass between that of Earth and that of Neptune," says Batygin. "Until now, we've thought that the solar system was lacking in this most common type of planet. Maybe we're more normal after all."

Brown, well known for the significant role he played in the demotion of Pluto from a planet to a dwarf planet adds, "All those people who are mad that Pluto is no longer a planet can be thrilled to know that there is a real planet out there still to be found," he says. "Now we can go and find this planet and make the solar system have nine planets once again."

## Mystery planets and strange orbits: what is lurking in the far reaches of our solar system?

Whether it&aposs &aposmy very early morning jam sandwich&apos or &aposmany vile earthlings&apos, everyone has a memorable way to list off the planets in our solar system.

But beyond the mnemonics, some of the most interesting and unexplored objects lurk beyond the stuff of textbooks in an icy region known as the Kuiper Belt.

This area of our solar system, which stretches out for billions of miles past Neptune, has been providing astronomers with a host of mysteries to solve over the past few years.

The most famous among the objects lurking beyond Neptune is many people’s favourite ‘planet’ Pluto which was robbed of the aforementioned title in 2006.

When Professor Mike Brown from Caltech discovered the dwarf planet Eris, the biggest object to be found in the solar system over the past 150 years, Pluto was demoted to dwarf planet status.

But planet or no planet, since Nasa’s New Horizons spacecraft reached Pluto in 2015 it has been repainting the picture we had of the world. Once considered an inactive clump of rock and ice, Pluto turns out to have much more of an atmosphere than we thought and is covered with icy mountain ranges, blocks of ice, craters and even snow.

It turns out Eris was only the beginning, though. Over the past few months, countless new icy objects have been found in the far reaches of the solar system, and the weird and wonderful orbits of some are difficult to explain.

Most recently, astronomers discovered what they believe to be a previously unseen dwarf planet called 2014 UZ224. It is said to be 330 miles (530km) across and was discovered on an eccentric, 1,140-year orbit 8.5 billion miles (13.7 billion km) from the Sun.

2014 UZ224 was found using what&aposs known as the Dark Energy Camera (DECam) as part of the Dark Energy Survey (DES) and this camera captures images of the sky at various intervals. Galaxies stay in a static position, but orbiting objects change their position and this was how the astronomers found 2014 UZ224.

According to Sky & Telescope, astronomers don&apost consider it part of the "classical Kuiper Belt" and instead is being referred to as a "scattered disk object" whose orbits has changed "due to encounters with Neptune".

The object has been confirmed by the International Astronomical Union&aposs (IAU) Minor Planet Center, but its orbital path is not yet known the IAU will need to officially classify it for it to be considered a dwarf planet.

Elsewhere, astronomers have also turned their attention to a bizarre new object, less than 124 miles (200km) across, just beyond the orbit of Neptune.

This TNO has been named ‘Niku’, a Chinese word for ‘rebellious’ because it has strange tilted orbit that sends it high above the flat orbital disk of the rest of the solar system. It seems to be part of a cluster of other related objects and icy planetoids with similar orbits.

Ying-Tung Chen of Academia Sinca in Taiwan, alongside an international cohort of astronomers from universities including Harvard, published a paper on arXiv about the mystery surrounding Niku.

One theory the team came up with is that a large object’s gravity is influencing the TNO, causing it to orbit at an angle to everything else, as well as backwards. However, it remains unclear what is actually going on.

Dr Matthew Holman, an astronomer at the Harvard-Smithsonian Centre for Astrophysics, was part of the team that discovered Niku. “It suggests there’s more going on in the outer solar system than we’re fully aware of,” Holman told New Scientist.

Moving on from Niku, one of the biggest mysteries that has come into the limelight this year is the question of whether a giant mysterious planet is lurking at the edge of our solar system.

Since an announcement was made at the start of this year, researchers have published a series of papers suggesting where the planet might be and how it could have formed. In 2014, Scott Sheppard and Chad Trujillo from the University of Hawaii proposed the potential existence of an additional planet.

In January this year, Caltech astronomers Professor Konstantin Batygin and Professor Mike Brown predicted the existence of what they, somewhat controversially, termed ‘Planet Nine’.

They used mathematical modelling and computer simulations to find the planet would exactly explain a strange clumping behaviour of a group of dwarf planets in the Kuiper Belt.

In order to arrive at this conclusion, Professor Batygin and Professor Brown ran computer simulations with input data based on the orbits of six extreme trans-Neptunian objects (ETNOs).

These ETNOs are called Sedna, 2012 VP113, 2004 VN112, 2007 TG422, 2013 RF98 and 2010 GB174. Since the paper was published in January, physicists and astronomers the world over have rushed to place their own constraints on the potential planet. But many believe the search still has a long way to go.

‘My own feeling is that we need a much larger sample size before I&aposm willing to call the available evidence compelling,’ Professor David Tholen, astronomer at the University of Hawaii, told WIRED. �rtainly an additional planet is consistent with the available evidence, but it could also simply be the statistics of small numbers.’

In fact, astronomers first considered the idea that Planet Nine could have had something to do with the strange orbit of the TNO Niku. However, they found that Niku and its associated planetoids were too close to the rest of the solar system to have potentially been tugged out of place by this mysterious object.

Earlier this year Professor Tholen and his colleagues produced a paper detailing the orbits of two new icy worlds in the Kuiper Belt. But these frozen potato-shaped rocks are unusual compared to other asteroids and comets in the region as their orbit seems to be in sync with Neptune despite being far away from the planet.

Their strange cosmic dance with Neptune could help reveal how the early solar system formed.

Professor Tholen is more interested in the dwarf planet Sedna, one of the ETNOs that has helped predict some constraints on the mysterious Planet Nine for the Caltech astronomers. He is currently trying to understand why Sedna is in the orbit it is currently in.

‘Most objects we can explain in terms of their gravitational interactions, but Sedna stays so far from the planets that its gravitational interaction is extremely weak,’ he told WIRED.

He says the only way to completely understand Sedna and its interactions, along with the other new worlds in the Kuiper Belt, is by observing them for longer - something which will continue to provide us with new discoveries.

So when it comes to the Kuiper Belt - watch this space. The evidence is mounting up for a possible extra planet, and some have suggested we might detect it by the end of this year.