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Is it possible that a planet larger than Earth exists, hidden from view, at the far reaches of our solar system?

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Many scientists have long believed so, and now, with the aid of a new telescope, their beliefs may soon be confirmed.

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Surely such a major discovery would be big news. It's not every day that new planets are discovered in our own planetary neighborhood.

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But, according to astronomer Scott Shepard of the Carnegie Institution for Science in Washington, D.C., the discovery did not happen suddenly.

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There was no eureka moment, he says. The evidence just built up slowly.

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Shepard and his collaborator Chad Trujillo of Northern Arizona University first published their suspicions about the unseen planet in 2014.

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Since then, the evidence for what the scientists call Planet X has continued to build.

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The first evidence of Planet X, or Planet 9 as it is more commonly known, was uncovered in January 2016 by a group of researchers at the California Institute of Technology.

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Astronomers Konstantin Batkin and Mike Brown led the research, which found the speculative planet through intensive computer modeling and mathematical predictions.

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Planet 9 has never been seen from Earth, but the object is believed to have at least 10 times the mass of our planet, as well as an incredible orbit of 10,000 to 20,000 years.

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Many scientists are growing increasingly excited at the prospect of confirming the existence of Planet 9.

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Much of this excitement centers on the opening of the Vera C. Rubin Survey Telescope, named after the astronomer who first discovered evidence for dark matter.

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The telescope will begin operating in 2022 when it could confirm the planet's existence outright or provide the crucial, confirmational evidence that it's there.

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An official discovery of the planet would be a major scientific event, but it would also throw our existing understanding of the solar system into chaos as it would challenge everything we know about how our planetary neighborhood was created.

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How, for example, could such a large planet have formed so far out from the Sun?

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Although Pluto is just two-thirds of the diameter of our Moon, it was originally classed as a planet.

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By the end of the century, however, as telescopes grew in size, astronomers were starting to detect an increasing number of small worlds beyond Neptune.

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Then, in 2005, Eris was discovered.

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It was at least the same size as Pluto and probably bigger.

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In other words, if Pluto was a planet, so was Eris.

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NASA hastily organized a press conference and announced their discovery.

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The journey towards Planet Nine began in 2012.

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Using the Inter-American Observatory's telescope in Chile, Shepard and Trujillo were finding more and more distant objects.

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One of these objects was catalogued as 2012 VP113 and nicknamed Biden after the U.S. Vice President at the time because of its VP designation.

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To their amazement, Biden followed a highly elliptical orbit, but that was not the most remarkable thing about it.

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It just so happened that Biden's orbit appeared strikingly similar to another distant world known as Sedna.

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Discovered in 2003, it immediately stood out because of its highly elliptical orbit, which swings from 76 AU to 937 AU.

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Objects like Sedna and 2012 VP113 can't form on these eccentric orbits.

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The most curious aspect, though, was that the two elongated orbits pointed in roughly the same direction.

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Indeed, the more the scientists' study progressed, the more it appeared that the orbits were aligned.

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It seemed as if something was corralling those tiny worlds, and the only thing capable of doing this was a much larger planet.

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After doing some further calculations, the scientists discovered that the potential planet would have to have had between 2 and 15 times the mass of Earth,

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on an orbit that lies on average somewhere between 250 AU and 1500 AU from the Sun.

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The scientists' results were published by the prestigious journal Nature in 2014, capturing the attention of the astronomical community worldwide.

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The following year, in 2015, Shepard and Trujillo were among the scientists who discovered 2015 TG387.

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Nicknamed the Goblin, it is the third most extreme object behind Sedna and Biden, and it too lines up, reducing still further the idea that this alignment is purely coincidental.

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In 2016, Brown and his collaborator Konstantin Bachchin published their own analysis of the data.

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They were largely in agreement with Shepard and Trujillo about the size and distance of the planet,

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and they even suggested an area of sky where they thought it might be found.

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But some scientists remain to be convinced.

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At the University of Pennsylvania, Pedro H. Bernardinelli recognized that there were other places scientists might search

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for distant, smaller worlds.

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He examined data from a cosmological survey designed to measure the way in which the universe is expanding by focusing on distant galaxies.

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He was hoping to find the celestial equivalent of a photobomb searching for distant objects in the solar system that just happened to obscure the camera.

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Amazingly, Bernardinelli found seven such objects.

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Initially, it looked as if the smaller worlds were also aligned as expected, but the more rigorously Bernardinelli analyzed the data, the weaker he felt the alignment became.

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We don't think we see the signal in our data, says Bernardinelli, although he acknowledges he cannot yet definitely rule out the planet's existence as he has yet to run the analysis on the full survey data.

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Our answer might change the next time we do this, he says.

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Nowadays, Shepard spends a considerable amount of his time using the Japanese Subaru telescope in Hawaii, patiently scouring the sky for conclusive evidence of Planet Nine.

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It's a daunting task, much like searching for the proverbial needle in a haystack.

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If it exists, Planet Nine is nonetheless a very faint object in a very large sky.

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But the task of finding it will be made easier with the aid of Rubin.

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Rubin is a telescope with the potential to devour the sky.

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While most telescopes could take years to survey the entirety of the sky, Rubin will accomplish the task in just three nights.

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It will then do this again and again and again to determine what has changed and to catch the moving objects.

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Currently under construction in Chile, it may take several more years before the telescope is fully operational.

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But it will be worth the wait.

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That survey is going to change solar system science as we know it, says Shepard.

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If Planet Nine is out there, Rubin should see it, says Meg Schwamm of Queen's University Belfast, who co-chairs the Rubin Observatory Solar System Science collaboration.

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That puts Shepard's world easily within its sights.

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If others haven't seen Planet Nine before our survey starts then, I think all eyes are on the Rubin Observatory, Schwamm notes.

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If the telescope fails to see the planet directly, it will still detect many other distant mini-worlds that can all be used to help more accurately triangulate the planet's position, thereby narrowing the search area.

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If Planet Nine really is out there, then the consequences will be far reaching.

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Today, astronomers believe that the solar system was formed from a disk orbiting our sun.

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It is thought that the matter was gradually condensed into smaller bodies, which then collided to form larger ones.

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At the end of this process, the planets were born.

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However, the matter in this disk thins out further from the sun, meaning there's not enough raw material to form a large planet in the distant solar system.

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To protect the standard theory, some scientists suggest that Planet Nine was once likely to become a gas giant akin to Jupiter or Saturn, and was so forming alongside them.

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The theory goes that a gravitational interaction stunted its growth by hurling it out into the dark.

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But this theory has its skeptics.

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Jacob Schultz of Durham University believes that, while it's possible, it actually requires quite a lot of coincidences.

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A single gravitational interaction cannot do the job on its own.

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Instead, a series of interactions is required to bring it into an orbit that will never take it back to where it formed.

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But Schultz does stop there with his theory.

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Along with his collaborator, James Unwin, of the University of Illinois at Chicago, Schultz has suggested that the object corralling these distant worldlets is perhaps not a planet of any kind, but a black hole.

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If this is the case, no one will be able to see it, not even Rubin, because black holes emit absolutely no light at all.

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They simply swallow light and anything else that happens to cross their path.

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It is a startling possibility because Schultz's black hole would, in theory, have to be part of a long suspected but never proved population of such phenomena that were formed shortly after the Big Bang.

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For now, however, most other astronomers seem reasonably satisfied with the idea that there's a large planet out there in the darkness just waiting to be discovered.

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The

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Thank you.

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Thank you.