The Mystery Straight Guy Edges Again

If Planet Nine exists, why has no i seen it?

(Image credit:

ESA/Hubble, Chiliad. Kornmesser

)

Strange things are happening at the outer edges of our solar system. An object upward to x times the mass of Earth is pulling others towards it. Is it a planet, or something else?

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Percival Lowell was a human of many errors.

The 19th-Century travel writer and businessman – fabulously wealthy, perennially moustachioed, and often plant in crisp 3-piece suits – had read a book on Mars, and on this basis, decided to go an astronomer. Over the coming decades, he made a number of wild claims.

First up, he was convinced of the existence of Martians, and idea he had constitute them (he hadn't). Others had documented strange lines traversing the planet, and Lowell suggested that these were canals, built as the last endeavor of a dying civilisation to tap water from the polar water ice caps. He used his fortune to build an unabridged observatory, just to become a meliorate look. It turned out they were an optical illusion, created by the mountains and craters on Mars when viewed through low quality telescopes.

Lowell also believed that the planet Venus had spokes – seen in his notes as spidery lines emanating from its centre (it doesn't). Though his assistants tried to detect them, it seemed that simply he could see this unexpected detail. Information technology's at present assumed that they were shadows cast from the irises in his own optics, as he looked through his telescope.

But most of all, Lowell was determined to find the ninth planet in our solar arrangement – a hypothetical "planet X", which at the time was idea to be responsible for the rogue orbits of the furthest-known planets from the Lord's day, the cool-bluish ice giants Uranus and Neptune. Though he never set eyes on this phantom behemoth, the quest consumed the last decade of his life – and after several nervous breakdowns, he died at the historic period of 61.

Little did he know, the search would notwithstanding be going – with a few tweaks – in 2021.

A false trail

Undeterred past his own bloodshed, Lowell left a million dollars to the cause of finding planet 10 in his volition. So, afterward a cursory interlude involving a legal battle with his widow, Constance Lowell, his observatory kept looking.

But 14 years later, on xviii February 1930, a immature astronomer was looking at two photos of star-studded skies, when he noticed a speck amongst them. It was a tiny world. He had found Pluto – for a while considered the elusive planet X.

Pluto was demoted to a dwarf planet in 2006, leaving an opening for a new ninth planet (Credit: NASA/ Johns Hopkins University /Southwest Research Institute)

Alas, information technology was not to exist. Soon scientists realised that this could non be what Lowell was looking for – information technology was not nearly big enough to pull Neptune and Uranus away from their rightful positions. Pluto was just an accidental interloper, which happened to be in the area.

The final blow to planet X came in 1989, when the Voyager two spacecraft swept by Neptune and revealed that it's fractionally lighter than anyone had originally idea. With this in heed, eventually a Nasa scientist calculated that the orbits of the outer planets had made sense all along. Lowell had instigated a search that had had never been needed.

Just only as the concept of a hidden planet was killed off, the groundwork was laid for its resurrection.

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In 1992, two astronomers who had "doggedly scanned the heavens in search of dim objects across Neptune" for years, according to Nasa, discovered the Kuiper Belt. This cosmic donut of frozen objects, extending just beyond the orbit of Neptune, is one of the largest features in the solar system. It'due south so vast, it's idea to contain hundreds of thousands of objects larger than 100km (62 miles) across, also equally upward to a trillion comets.

Soon scientists realised that Pluto was unlikely to be the simply large object in the outer reaches of the solar arrangement – and began to question whether it was actually a planet at all. And then they found "Sedna" (around 40% of the size of Pluto), "Quaoar" (effectually one-half the size of Pluto), and "Eris" (nearly the same size as Pluto). Information technology became clear that astronomers needed a new definition.

In 2006, the International Astronomical Union voted to bench Pluto's condition to a "dwarf planet", along with the newcomers. Mike Dark-brown, a professor of planetary astronomy at the California Plant of Technology – Caltech – who led the team that identified Eris, is self-styled as the "man who killed Pluto" to this day. The ninth planet was no more.

A ghostly signature

At the aforementioned time, the discovery of these objects uncovered a major new lead in the search for a hidden planet.

It turns out that Sedna is not moving in the fashion everyone expected – tracing elliptical rings effectually the Sun, from inside the Kuiper Belt. Instead, this dwarf planet takes a bizarre and unexpected path, swinging from just 76 Earth-Sun distances (roughly 11 billion k/seven billion miles) from the heart of our solar system to more than 900 (roughly 135 billion km/84 billion miles). Its orbit is so meandering, information technology takes 11,000 years to complete – the last fourth dimension Sedna was at its electric current position, humans had simply just invented farming.

Percival Lowell established his observatory in Flagstaff, Arizona to look for intelligent life on Mars. Somewhen it was used to detect Pluto (Credit: Alamy)

It's as though something is tugging at Sedna and dragging it away.

Enter a hypothetical new addition to our solar arrangement – but non every bit information technology was thought of earlier. In 2016, the same Mike Brown who had slain Pluto, together with his colleague Konstantin Batygin – too a professor of planetary scientific discipline at Caltech – co-authored a paper proposing a massive planet, between five and x times the size of Earth.

Their idea came from the observation that Sedna was non the only object out of place. It was joined past half dozen others, and all of them are being pulled in the same direction. There are also other clues, such equally the fact that each is tilted on its centrality in exactly the same direction. The pair calculated that the probability of all six objects beingness pulled in the exact same direction, with the aforementioned tilt by chance was just 0.007%.

"We idea 'this is quite interesting – how tin can this exist?'" says Batygin. "It was quite remarkable because such a clustering, if left alone for a sufficiently long period of fourth dimension, would disperse, but due to interaction with the gravity of the planets."

Instead, they proposed that Planet Nine had left its ghostly banner in the outer reaches of our solar organization, distorting the orbits of the objects effectually it with its gravitational pull. Several years on, and the number of objects that fit the eccentric orbital pattern and tilt has continued to increase, "We at present take effectually nineteen overall," says Batygin.

Though no one has yet seen the hypothetical planet, information technology'southward possible to infer a surprising amount nearly it. As with the other objects across the Kuiper Belt, the orbit of the new Planet Nine would exist and then distorted that its farthest reach is expected to be twice equally far away equally its nearest – around 600 times the distance from the Lord's day to Globe (90 billion km/56 billion miles), vs 300 (45 billion km/28 billion miles). Scientists accept too hazarded a gauge at its aesthetic – icy, with a solid core, like Uranus or Neptune.

Then in that location'due south the slippery question of where Planet Ix might have come up from in the first place. So far, in that location are iii main ideas. One is that information technology formed where it currently hides, which Batygin dismisses as relatively unlikely because this would require the early on solar system to have stretched out as far as its afar refuge.

In that location's likewise the intriguing proffer that the ninth planet is actually an alien imposter, an object that was stolen from some other star long ago when the Sun was still in the stellar cluster in which it was born. "The problem with such a story is that you're just as likely to so lose the planet upon the next encounter," says Batygin. "And then, statistically, that model runs into trouble."

Neptune is currently the about distant known planet in our solar system, merely there might exist another lurking across the Kuiper Belt (Credit: Nasa/JPL)

Then in that location's Batygin's personal favourite, which he admits is also "not a complete slam douse". In this scenario, the planet formed much closer to the Sunday, at a fourth dimension when the solar arrangement was in its early stages and the planets were just beginning to coagulate out of the surrounding gas and dust. "It kind of hung around the giant planet formation region, before being scattered out past Jupiter or Saturn, and subsequently had its orbit modified by passing stars," he says.

An obscure hiding place

Of course, all this begs an obvious question – if Planet Nine is really in that location, why has no one seen information technology?

"I didn't have a peculiarly potent appreciation for but how difficult would exist to discover Planet 9 until I started looking together with Mike using telescopes," says Batygin. "The reason it'due south such a tough search is because most astronomical surveys are not looking for a unmarried affair."

For example, astronomers would usually be looking for a class of objects, such every bit a particular kind of planet. Even if they're rare, if you survey a wide plenty expanse of space, y'all're likely to find something. Merely hunting down a specific object such as Planet Ix is a whole unlike do. "In that location's only 1 tiny portion of the heaven that has it," says Batygin, who explains that another gene is the slightly more prosaic challenge of booking time slots to use the right kind of telescope.

"Really, at the moment the only game in town for finding Planet 9 is the Subaru Telescope," says Batygin. This eight.2m behemoth – located at the summit of a dormant volcano, Maunakea, in Hawaii – is capable of capturing fifty-fifty the weak light of distant celestial objects. This is platonic, because the shadowy planet would be so far away, it'due south unlikely to be reflecting much light from the Lord's day.

"We have only 1 auto that we tin use, and we get maybe three nights on it a year," says Batygin, who was fresh from a three-dark run on the telescope the previous week. "The good news is that the Vera Rubin telescope is coming online within the next couple of years, and they are going to probably detect information technology." This side by side-generation telescope, currently nether construction in Chile, will be scanning the heaven systematically – photographing the entire available view – every few nights, to survey its contents.

An intriguing culling

However, there is one almost outrageously peculiar scenario in which the planet will never be plant this way – it might non exist a planet after all, just a black hole.

The Subaru telescope in Hawaii has already spotted the about distant known object in our solar organisation, nicknamed "Farfarout", during a search for Planet Nine (Credit: Alamy)

"All of the bear witness for there existence an object is gravitational," says James Unwin, professor of physics at the University of Illinois, Chicago, who first suggested the idea, along with Jakub Scholtz, a postdoctoral researcher from the University of Turin. While we're near familiar with the thought that planets exert a powerful gravitational pull, "there are other things that can generate it, which are more exotic", says Unwin.

Some plausible replacements for planet nine include a small ball of ultra-full-bodied nighttime matter, or a primordial blackness hole. Equally black holes are among the virtually dense objects in the Universe, Unwin explains that it's entirely possible the latter could be warping the orbits of distant objects in the outer solar system.

The blackness holes we're most familiar with tend to include "stellar" black holes, which have a mass that'southward at least 3 times that of our own Lord's day, and "supermassive" black holes, which are millions or billions of times our Sun's mass, While the sometime are born out of dying stars collapsing in on themselves, the latter are more than mysterious – possibly start as jumbo stars which implode, and then gradually accrue more and more mass by devouring everything in their surroundings, including other blackness holes.

Primordial black holes are different. They take never been observed, but are thought to originate in the hot energy-and-matter haze that formed in the first second of the Big Bang. In this uneven environment, some parts of the Universe may take become then dense, they were compressed into tiny pockets with the mass of planets.

Unwin points out that there is zero probability of the blackness hole being formed from a star, since they continue their potent gravitational pull – it'south just concentrated. Even the smallest stellar blackholes have masses 3 times that of our Dominicus, and then information technology would be similar having at to the lowest degree three extra Suns pulling at the planets in our solar system. In brusque, nosotros would definitely accept noticed.

However, Unwin and Scholtz say information technology could exist a primordial black hole, since these are thought to be substantially smaller. "Considering these things are born during the early on stages of the Universe, the dense regions they formed from could take been particularly small," says Scholtz. "As a outcome, the mass independent in this black pigsty that eventually is formed out of information technology tin can be much, much less than a star – they fifty-fifty can be merely a couple of pounds, like a chunk of stone." This is more in line with the predicted mass of Planet Nine, which is thought to be equivalent to upward to ten Earths.

The dwarf planet Sedna has an unconventional orbit which might exist explained by the gravitational pull of a massive undiscovered planet (Credit: Nasa/ JPL-Caltech)

What would it look similar? Should we be worried? And could this exist fifty-fifty more exciting than discovering a planet?

First, even primordial black holes are dense enough that no light tin can escape. They are the truest form of black. This means that this ane would not show up on any kind of telescope that currently exists. If you were to look straight at it, the only clue to its presence would be a bare void – a tiny gap in the blanket of stars in the night sky.

Which brings us to the real snag. While the mass of this black hole would be the same as that of the proposed Planet 9 – upward to 10 times World's – it would be condensed into a volume roughly the size of an orange. To notice it would require some ingenuity.

So far, suggestions include looking for the gamma rays that are emitted past objects as they autumn into blackness holes, or releasing a constellation of hundreds of tiny spacecraft, which might – if we're lucky – pass close plenty so that they'd exist pulled towards information technology ever-then-fractionally, and accelerate by a detectable amount.

Since the mysterious gravitational pull is emanating from the farthest reaches of our solar system, the probes would have to be sent via an Earthbound laser array, which could propel them to 20% of the speed of lite. If they travelled whatsoever slower, they might accept hundreds of years to arrive – an experiment that would, naturally, stretch well beyond a human being lifetime.

As information technology happens, these futuristic spacecraft are already being developed for some other ambitious mission, the Breakthrough Starshot project, which aims to ship them to the Blastoff Centauri star system, 4.37 lite-years away.

If we were to detect a lurking black pigsty, rather than a frigid planet, Unwin says at that place would be no need to panic. "There'south a supermassive black hole in the centre of our galaxy," he says. "But we don't worry well-nigh our solar system falling into it, because we're in a stable orbit around information technology." And so, while a primitive black pigsty will suck up annihilation within its path, this would non include the Earth, which – like the other inner planets – doesn't ever come up close.

"Information technology's not like a vacuum cleaner," says Unwin. He explains that from the perspective of anyone on Earth, having an undiscovered black pigsty in the solar system is non that dissimilar to having a concealed planet there.

But while stellar and primordial black holes are essentially the same, the latter take never been found or studied – and departure in scale is expected to lead to some bizarre phenomena. "I would say that the things that happen with small black holes are more interesting than what happens with large black holes," says Scholtz.

In 2019, the Result Horizon Telescope (EHT) captured an image of the shadow of a supermassive blackness hole in the centre of the galaxy Messier 87 (Credit: Alamy)

One example is the aptly-named process of "spaghettification", which is frequently illustrated past the fable of an astronaut who ventured too near a black pigsty'south upshot horizon – the point beyond which no light can escape – and fell in headfirst. Though her head and feet were just metres from each other, the difference in the gravitational forces acting on them would be so great, she would exist stretched like spaghetti.

Intriguingly, the effect should exist fifty-fifty more than dramatic, the smaller the black pigsty is. Sholtz explains that information technology'due south all well-nigh relative distances – if you're two metres tall, and you're falling through an outcome horizon that'due south i metre from a primordial black hole's centre, the discrepancy betwixt the location of your caput and feet is larger, compared to the size of the black pigsty. This means you'll be stretched far more than if yous fell into a stellar 1 that's a million miles across.

"And and so, peculiarly plenty, they're more interesting," says Scholtz. Spaghettification has already been seen via a telescope, when a star got too close to a stellar black pigsty 215 million calorie-free years from Earth, and was ripped apart (no astronauts were harmed). But if at that place is a primordial blackness hole in our own solar arrangement, it would provide astrophysicists with the opportunity to study this behaviour – and many others – up close.

So what does Batygin make of the possibility that the long-sought 9th planet could really exist a black hole instead? "It'south a creative idea, and we cannot constrain what its composition is even in the to the lowest degree scrap," he says. "I recall maybe it's just my own bias, being a planetary science professor, but planets are a lilliputian chip more than common…"

While Unwin and Scholtz are rooting for a primeval blackness pigsty to experiment with, Batygin is merely as keen for a giant planet – citing the fact that the about common type throughout the galaxy are those which take around the same mass as Planet 9.

"Meanwhile well-nigh exoplanets that orbit Sun-like stars, are in this weird range of existence bigger than the Earth and considerably smaller than Neptune and Uranus," he says. If scientists do find the missing planet, information technology volition be the closest they tin can go to a window into those elsewhere in the milky way.

Only time volition tell if the latest quest will be more successful than Lowell'due south. But Batygin is confident that their missions are totally dissimilar. "All of the proposals are quite singled-out in both the data they seem they seek to explain, likewise every bit the mechanisms they employ to explicate it," he says.

Either mode, the search for the legendary ninth planet has already helped to transform our understanding of the solar system. Who knows what else we'll find before the hunt comes to an terminate.

Zaria Gorvett is a senior journalist for BBC Futurity and tweets @ZariaGorvett

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This story was updated on 22/two/2021. An earlier version incorrectly stated that the Voyager two mission led to the discovery of the Kuiper Belt.

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Source: https://www.bbc.com/future/article/20210216-the-massive-planet-scientists-cant-find

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