Photo: Nasa
Photo: Nasa

Is Planet Nine the new X?

Sorry conspiracy theorists, Planet Nine is not Eris or Sedna or any other object we have already seen and named and catalogued

Is the new theoretical Planet IX the same as the old mysterious Planet X or the notorious Nibiru?

Short answer: Nope.

To understand why people want to revive Nibiru and Planet X conspiracy theories, we need to go back all the way to 1781. The late 18th century was a turning point in the history of astronomy, when a slew of discoveries not only extended the boundaries of the known solar system, but also almost doubled its size.

The heliocentric model had been established and those who could afford it had started pointing telescopes up at the sky, meticulously cataloguing a multitude of stars, nebulae and objects that would eventually become galaxies. Within our solar system, amateur astronomers were discovering planetary moons all over the place. Till Saturn, that is. In the mid-18th century, our solar system had only six planets.

Despite Uranus being visible to the naked eye, it was never classified as a planet by ancient astronomers, who seemed to have mistaken it for a star due to its very slow motion. Budding musician William Herschel, who had been introduced to the telescope by fellow musicians, made the same error when he was cataloguing stars.

After multiple observations and study of orbit, however, Herschel concluded that the body he was observing was a planet. Thus, Uranus, despite being visible to the naked eye, became the first planet to be discovered using a telescope.

Soon after, it was observed that Uranus had irregularities in its orbit that could not be explained by classical mechanics. It was being pulled slightly away from its orbit in its path around the sun, behaviour that can only be explained by the existence of another unknown body. But hunting for an unknown body is not as easy as “point telescope and wait". You need to know exactly where to look, and how long to look for. But an easier way is to look for gravitational signatures of a planet.

So, instead of blindly searching for this other planet that is tugging at Uranus, French mathematician Urbain Le Verrier in 1846 observed and calculated with precise numbers the location and size of the new planet beyond it. And so, the existence of Neptune was predicted and calculated before the planet was hunted for and found—using mathematics alone—in what was one of the most extraordinary achievements in science.

The study, use and advancement of telescopes were growing at such a pace, alongside intense competition for credit among astronomers, that Neptune’s giant moon Triton was discovered a mere 17 days after the planet itself.

However, all of this didn’t entirely solve Uranus’s problem. It was still showing discrepancies in orbit, despite the discovery of Neptune and calculation of how much Neptune’s gravity should affect Uranus. In fact, even Neptune seemed to be wiggling a bit in its orbit.

These perplexing observations led to the conclusion in the wake of a predicted discovery that yet another planet exists beyond Neptune that perturbs the orbits of both Uranus and Neptune. So, a massive search for a mysterious planet, dubbed “Planet X", was launched.

Meanwhile in Kansas, an amateur astronomer named Clyde Tombaugh was playing with telescopes, constructing a few in his backyard. His skills with the telescope immediately got him a job at the Lowell Observatory, which had been studying Mars, but had now turned its giant telescopic head towards the elusive Planet X.

William Pickering, the astronomer who constructed the telescope at Lowell, had calculated the location and orbit of Planet X and Tombaugh’s job was to use the telescope to find it. The telescope at Lowell took two pictures of the same area of the sky on two different days.

When the two starfield images were compared, distant objects like stars and galaxies would seem to remain stationary, whereas bodies that were closer to the Earth, like planets, would move. Each image of the sky contained anywhere from 10,000 to one million stars and Tombaugh’s very tedious job was to “blink" two images and find a body that moved in them.

He did find one. Pluto’s discovery was announced on 13 March 1930. A call was put out to the public to send in suggestions for the newly found planet’s name. Venetia Burney, the 11-year-old granddaughter of a librarian in England, suggested “Pluto" as the distant planet seemed to her to resemble the guard of the underworld.

The name was quickly accepted through a landmark unanimous vote in Lowell Observatory, primarily because the first two letters formed the initials of Percival Lowell, barely two months after the discovery of the body itself. Pickering, whose career had by now devolved to making claims of finding lunar insects and flora, died a happy man on 17 January 1938.

However, observations of Pluto seemed to suggest that it did not fit into the description of Planet X. Initial estimates of mass placed Pluto on a par with Earth, but its mass was revised downward for decades following its discovery, with values ranging from the mass of Mars to almost 1% of the mass of Earth.

When the existence of Pluto’s gigantic moon Charon was confirmed in 1978, astronomers could study their gravitational interaction and accurately deduce Pluto’s mass for the first time. It was less than 0.3% of Earth’s.

Meanwhile, the mystery of Uranus and Neptune’s orbital perturbations was solved when Voyager 2 studied Neptune in 1989. Three years later, it was found that the mass of Neptune was much less than what scientists on Earth believed, and the new numbers fit perfectly well into the gravity equation with no discrepancy, ending the search for Planet X once and for all.

There had earlier been a rabid search for another hypothetical planet named Vulcan, which was supposed to have existed between Mercury and the sun. It was again predicted by Le Verrier at the same time as Neptune, but its existence was nearly quashed as soon as Albert Einstein unleashed his theory of General Relativity. Vulcan was put to rest once and for all when Nasa’s solar mission probes actively hunted for it in 2006 and failed to find anything between Mercury and the sun.

Pluto, however, continued to grab the limelight, primarily because of sudden barrage of discoveries of objects around it in the 1990s. These objects were discovered in the region of space we now called the Kuiper Belt. The Kuiper Belt sits just beyond Neptune, at 30 AU, and extends up to 50 AU. (1 AU or astronomical unit is the mean distance between the Earth and the sun. It is 149,597,871km, to be exact.)

These incessant findings of new objects in the Kuiper Belt, called Kuiper Belt Objects, or KBOs for short, started throwing doubts on Pluto’s status as a planet. By the late 1990s, there was unofficial acceptance all over in the astronomy community of Pluto simply being the “largest of a number of icy bodies" found beyond Neptune.

Astronomers differed greatly on Pluto’s status and there was constant controversy whenever it was omitted or presented in a solar system model. Many planetariums removed Pluto from their models as well.

Neil DeGrasse Tyson, the director of Hayden Planetarium, famously omitted Pluto when his solar system model reopened in 2000 for the public. Tombaugh, the discoverer of Pluto, who fought throughout his life to retain Pluto’s planetary status, died a distressed 59 years to the day after the death of Pluto’s predictor, Pickering.

As the debate raged on, a group of astronomers at Caltech was obsessively studying the Kuiper Belt. This group, comprising of Mike “Pluto Killer" Brown, Chad Trujillo and David Rabinowitz, announced in 2005 the discovery of another massive object near Pluto—more massive than Pluto still.

The team nicknamed this object Xena, after the fictional warrior princess, partly because it began with an “X" (Planet X) and partly in an effort to introduce more female mythological names into the ever-growing astronomical bodies database.

Xena was much more massive than Pluto and added a lot of fuel to the burning fires of planetary definitions. Along with Xena, astronomers had also discovered two other KBOs, nicknamed Easterbunny and Santa. The controversy further intensified when it was discovered Xena had a moon.

Finally, in August 2006, a conclusion was reached by the International Astronomical Union (IAU) in Prague, where a new set of definitions were accepted for the designation of a planet. Under the new guidelines, a body needs to have “cleared its neighbourhood" to be considered a planet.

Clearing neighbourhood here does not mean absence of other bodies nearby; gigantic planets do have a multitude of moon and rings after all. It means being the gravitationally dominant force in the region. Think of a planet sweeping out all bodies around its orbit using its gravitational influence as it moves along its path around the sun.

Gravitationally dominant bodies are not under the influence of any other comparable massive body and also do not have comparatively massive bodies except for satellites near them. They also should be capable of pulling nearby objects towards them or slingshotting objects away from them. Pluto, unfortunately, is surrounded by many bodies that are of comparable size and are too massive to be affected by Pluto’s gravity.

This new definition of a planet demoted Pluto officially from its position as the ninth planet in our solar system. Pluto, along with other KBOs, were then classified as dwarf planets. Official names announced for the newly appointed dwarf planets Xena, Easterbunny and Santa were Eris (“ee-ris"), Makemake (“maaki-maaki") and Haumea (“how-may-aah"), respectively.

Eris is the Greek goddess of chaos, who frequently stirs up jealousy and wars, a fitting name as the IAU’s decision is controversial to this day. In a sleight of hand, Eris’s moon was named Dysnomia. In Greek mythology, Eris’s daughter Dysnomia is the goddess of lawlessness; Xena the warrior princess was portrayed by the actress Lucy Lawless.

Pluto was not the first planet to be accepted as a planet and then reclassified as not being one. Ceres (“see-res"), the last of the five dwarf planets that orbits in the asteroid belt between Mars and Jupiter, was discovered in 1801. It immediately became known as the eighth planet (Neptune had not yet been discovered). And from eight, our solar system expanded to nine in less than half a decade. Vesta, a very large asteroid in the same region, was discovered in 1807 and immediately pronounced a planet.

But then, as amateur astronomers started discovering more and more asteroids, they realized that these are large rocks and not really planets. Promptly, without so much as a peep of the resistance Pluto had, the two were dropped and reclassified.

Back to 2006, the focus now shifted to the Kuiper Belt as a whole instead of just Pluto. The Kuiper Belt is over 30 times as far away from the sun as we are, and hosts a tremendous amount of icy objects, including comets. The Kuiper Belt is home to three dwarf planets: Pluto, Haumea, Makemake. The next obvious question would be the location of Eris.

Eris, frequently called Pluto’s twin because it is 27% more massive than Pluto but only 5% lesser in size, has an orbit that’s considerably more exaggerated than Pluto’s. An elongated orbit, like Pluto’s, makes Eris’s closest approach to the sun (perihelion) at 37 AU. While that falls within the Kuiper Belt region, its farthest approach (aphelion) is almost 97 AU, putting it way out of the Kuiper Belt. Hence, it is classified as a Trans-Neptunian Object (TNO).

It was eventually concluded that Eris was flung out of the Kuiper Belt by gravitational interaction with Neptune. This is a common phenomenon. Just like how spacecraft fly very close to massive planets for gravity assist, other objects that come close to such bodies get a “kick". They can then be pulled in towards the inner solar system or get thrown out of their orbits into higher orbits or get chucked out of the solar system entirely!

Comet Catalina, which is currently visible over the Earth, is on its way out of the solar system, having had its orbit change into an ejection trajectory by none other than our sun.

Eris is not the only body with an unnaturally elongated orbit we know. Yet another TNO was discovered by the same team that discovered Eris at Caltech orbiting at 75 AU to a whopping 935 AU. It is the longest orbiting object ever directly observed, to this day. Its orbital period is 11,400 years and moves farther than any object in the solar system we have seen except for comets. Fittingly, it was called Sedna, after the Inuit goddess of the Arctic who lives in the deep ocean.

Sedna orbits in the region of space called the Oort Cloud. You thought the Kuiper Belt was far at 50 AU? Oort Cloud spans the region of the solar system at distances from 2,000 AU to a mind-boggling 200,000 AU. This Oort Cloud is a sphere around our solar system and its end marks the end of the influence of the sun. Most of our comets come from here.

The inner part of the Oort Cloud is imaginatively named the Inner Oort Cloud and forms a disc instead of the sphere. This extends from 2,000 to 20,000 AU and Sedna is the first object to be discovered from there.

Very quickly, this prompted numerous theories about how the minor planet got there. (Anything anywhere that is not a planet or a comet is a minor planet, by the way. Not at all confusing.) One such theory is that there is a companion star to the sun called Nemesis orbiting somewhere beyond Neptune and which flings comets inwards towards us leading to all the mass extinctions we have had. No such star has been found.

Another popular theory is the existence of an undiscovered planet somewhere at 15,000 AU—that’s right—called Tyche. No such planet has been found either.

But Sedna isn’t the only minor planet with elongated, eccentric, unusual orbits. In 2014, 2012VP113 was discovered, orbiting between 80 AU and 450 AU.

The Inner Oort Cloud finally brings us to Planet Nine. Once again, Brown at Caltech (at this point, let’s just unanimously agree that Caltech and people who work with Mike Brown are the gods of the TNOs) has found tantalizing evidence of a planet there.

The discovery of this Planet Nine was released in the form of a paper co-authored by Brown with the primary author Konstantin Batygin, published in the Astronomical Journal on 20 January. In the paper, Batygin and Brown assert that they have found evidence of a body with enough gravity to have cleared its neighbourhood.

Remember a vacuum cleaner that goes around sucking in or pushing away everything in its path? The pushing away part of that leaves distinct signatures in the form of disturbed orbits. And if these bodies are all plotted on a graph or fed into a simulator, the vacuum cleaner’s path is traced in space. Thus, the orbit of the planet is deduced.

Also remember how gravity is a function of mass? Studying the masses and the extent of deflection of these bodies also can help in calculating the approximate mass of the vacuum cleaner planet.

For about 10 years, since the discovery of Sedna, really, astronomers had been observing that certain bodies that have extremely elongated orbits in the Kuiper Belt and beyond tend to show a pattern. Six of them, to be precise. They all seem to have been pushed away by something into orbits that fling out of a point. Each of their orbits are angular to the plane of the solar system on which rest of the planets orbit. They are all on the same plane as the theorized Planet Nine. It’s almost as if all these bodies came close to Planet Nine and received a gravitational kick that realigned their orbits.

Additionally, some objects seem to have realigned themselves perpendicular to this plane, possibly by receiving a kick in the other direction.

Batygin and Brown fed all the data into a simulator and it threw up a planet as the most probably cause. They concluded that there is a giant planet in the nether regions of the solar system, something that’s big enough to mess with the orbits of bodies that travel out into the deep ends and beyond the Kuiper Belt.

The existence of such a planet actually fits neatly into many models that aim to explain the formation of planets. Some scientists theorize that like Pluto, Sedna and Eris, many other bodies formed in the regions beyond Jupiter and Saturn at the beginning of the solar system. And some of them would have come too close to the giants, causing them to get kicked out into the far depths of the Kuiper Belt.

This could very well include a large planet that’s a bit smaller than Neptune. Batygin and Brown have put forth a few details gleaned from their research: Planet Nine is 10 times or more massive than Earth, is twice to four times as big as Earth, and orbits at 200 AU to 1,200 AU with an orbital period of 10,000 to 20,000 years.

The numbers fit well to explain what they observe. A giant icy planet would definitely explain the formation and queer orbits of a lot of bodies in and beyond the Kuiper Belt. It would also explain why all of the big planets and the asteroid belt are on one plane while things get crazy and all over the place just beyond Neptune. Planet Nine fits all the signs.

But there still isn’t solid evidence of Planet Nine actually existing. None of this means that it actually does. However, we can say with a fair bit of certainty that it does. Why? Because Batygin and Brown explicitly set out to disprove that such a planet exists. Two years ago, when they started working on the data of orbital patterns in TNOs, a planet was the quickest and easiest explanation to resort to without work. So, they got together and rigorously researched into every alternative explanation to prove the planet idea was wrong. And spectacularly failed.

Planet Nine has gravitational signatures all over the place. It’s only left to be seen through a telescope. So, is Planet Nine truly “discovered"? The line between prediction and discovery is a thin one here, but for all practical purposes, a new planet has not been discovered, merely theorized by observational evidence.

A body is not “discovered" till it is directly observed by human or telescopic eyes. What we have is theoretical evidence about a “likely" explanation for scattering of TNOs, which can be explained by the existence of a planet. Since it is the strongest and probably the most probable explanation, you just might as well say “discovered", but if you want to be pedantic and correct, Planet Nine is theorized and predicted, nothing more. At least, there will definitely be no official name till it is truly observed directly through a telescope.

What’s next for observation then? We need to wait and watch. We now know the orbit of the planet reasonably well. So, we can trace its path around the sun to a certain degree. However, we don’t know where on its orbit it is, which makes finding it hard.

Batygin and Brown have already eliminated regions in the orbit that amateur astronomers would be familiar with, and are focusing on finding it elsewhere. It will be found in the same way as Pluto was: a telescope takes multiple images of the same starfield separated by a few hours or days, and the images are blinked against one another to find a body that moves. Planet Nine, even at its apogee, will be bright enough to be spotted. So, we wait while astronomers search.

When the planet is discovered, if it is discovered, a new chapter in science would have been opened. There will be debates about who the discovery of the planet will be credited to: the observer or Batygin and Brown. There will be a hunt for moons to better understand it and accurately determine its mass and composition. There will be more speculation about bigger bodies in and beyond the Kuiper Belt, possibly transforming the way we picture the region of solar system beyond Neptune.

We do not know a lot about what is beyond the Kuiper Belt, but even indirect evidence of a theoretical planet is a big deal today and takes us one step closer to understanding and accepting that very large bodies could be at play there.

As the details of our solar system come into focus, our knowledge of the cosmos expands further and further. Perhaps most important of all, the more we learn about the solar system, the more our physics evolves.

But the conspiracy theorists can rest here. Planet Nine is not Pluto. It is not Eris or Sedna or any other object we have already seen and named and catalogued. It is also nothing that has captured pop culture in the past few decades. It’s not Tyche, it’s not Nemesis, it’s not even close to Planet X or Nibiru, both ideologically and in distance. Best let sleeping fictional planets lie. And if someone even says Vulcan, run.

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