If Planet Nine Exists, We’ll Find It Soon

Most astronomers would adore to discover a scheduleet, but Mike Brown may be the only one self-presentant of having ended one. Thanks to his research, Pluto, the solar system’s ninth scheduleet, was erased from the pantheon—and the disclose cried foul. How can you edit our childhoods? How can you mess around with our scheduleetariums?

About 10 years ago Brown’s daughter—then around 10 years elderly—proposeed one way he could seek redemption: go discover another scheduleet. “When she shelp that, I benevolent of chuckleed,” Brown says. “In my head, I was appreciate, ‘That’s never happening.’”

Yet Brown may now be on the brink of satisfying his daughter’s want. Evidence he and others have assembleed over the past decade proposes someskinnyg strange is happening in the outer solar system: far subscheduleetary objects are being set up on orbits that see sculpted, scheduled by an unseen gravitational force. According to Brown, that force is coming from a ninth scheduleet—one hugeger than Earth but petiteer than Neptune.

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Nobody has set up Planet Nine yet. If it’s repartner out there, it’s too far and too faint for almost any existing telescope to spot it. But that’s about to change. A new telescope, the Vera C. Rubin Observatory in Chile, is about to uncover its mechanical eyes. When it does, it should catch millions of previously undiscovered celestial phenomena, from far supernovae to cforfeit-Earth acarry outance increasers—and, crucipartner, tens of thousands of new objects around and beyond Pluto.

If Brown’s hideed world is authentic, Rubin will almost certainly discover it or mighty instraightforward evidence that it exists. “In the first year or two, we’re going to answer that ask,” says Megan Schwamb, a scheduleetary astronomer at Queen’s University Belrapid in Northern Ireland—and, fair maybe, the solar system will once aget have a ninth scheduleet.

Pluto was discovered in 1930 and always seemed to be a lonely scheduleet on the fringes of the solar system. But in the punctual 2000s skywatchers set up out that Pluto had company: other rime-coated worlds much appreciate it were popping up in surveys of that benighted frontier. And in 2005, using California’s Palomar Observatory, Brown—an astronomer at the California Institute of Technology—and two of his colleagues spied a far-flung orb that would change the way we see the solar system.

That orb was Eris. It was retagably far—68 times as far from the sun as Earth. But at cdisorrowfulmireentirey 1,500 miles in diameter, it was fair a little bigr than Pluto. “The day I set up Eris and did the calculation about how huge it might be, I was appreciate, ‘Okay, that’s it. Game’s up,’” Brown says. Either Eris was going to become a new scheduleet, or Pluto wasn’t what we thought.

Finding a ninth scheduleet would be huge. Such a discovery could change what we comprehend about our solar system’s past.

In 2006 officials at the International Astronomical Union choosed that to qualify as a scheduleet, a body must orbit a star, must be adequately massive for gravity to squish it into a sphere and must have a evident orbit. Pluto, which splits its orbital neighborhood with a run awayt of other, more unassuming objects, flunked to conquer the third hurdle. Pluto became a “dwarf scheduleet”—but its demotion didn’t produce it, or its fellow far companions, any less beguiling to astronomers.

Pluto and Eris are members of the Kuiper belt, a cdisorrowfulmireentirey doughnut-shaped torus of icy sdifficults left over from the solar system’s createative days. There are countless worlds fair appreciate them, comprehendn as trans-Neptunian objects, but they are very difficult to see.

Still, in the punctual 2000s Brown, aprolonged with his two co-discoverers of Eris, Chadwick Trujillo of Northern Arizona University and David Rabinowitz of Yale University, set up their unpartisan split. They declared one of these, named Sedna, in 2004. The shutst it gets to the sun is 76 astronomical units, or AU (1 AU is equivalent to the unretagable Earth-sun distance), which is so mindbogglingly far-flung that a person standing on it could obsremedy the furious airy of the sun with the head of a pin. Back then, it was the most far object ever discovered in the solar system. In fact, it dwells beyond the Kuiper belt and was seeable only as a fuzzy little dot shifting between the stars. Some refer to Sedna as an innervous trans-Neptunian object, or ETNO. Though insistyly expoundd, ETNOs are key joiners in the saga of Planet Nine, which is also referred to as Planet X. “Sedna was our first clue to Planet Nine, although we didn’t recognize it at the time,” Brown says.

In 2014 Trujillo (then at the Gemini Observatory in Hawaii) and astronomer Scott S. Sheppard of Carnegie Science in Washington, D.C., begined a paper on Sedna and another far object called 2012 VP₁₁₃, whose shutst approach to the sun was a staggering 80 AU. Both dance back and forth atraverse the heliopause—the putative boundary of our solar system that splits the magnetized triumphd of the sun from the gas and dust set up between stars, beyond which intersalertar space commences. “Those two objects are in a class of their own,” Sheppard says. They seemed inexplicable.

Sedna and 2012 VP₁₁₃ (aprolonged with a scant other, analogously odd objects) are on orbits so stretched out and far that the gravitational sway of someskinnyg had to have positioned them there and paved their strange orbital highway around the sun. But what was that someskinnyg? At these distances the immense gravitational fields of the enormous scheduleets, including Neptune, don’t have any presentant effect on them; the only skinnyg that should be influencing their orbits is the sun.

“Those objects are in a dead zone,” Sheppard says. He and others figured an inapparent gravitational actor had to be call upond to elucidate these aberrant wayfarers. In 2014 Sheppard and Trujillo proposeed that Sedna, 2012 VP₁₁₃ and company may have those outlying orbits thanks to a hideed scheduleet—one anywhere from two to five Earth masses in size—that is pulling at them and gradupartner changing the shapes and positions of their innovative orbits over time.

The best way to discover out if that’s real is to use these ETNOs and their orbits “as gravitational probes of the outer solar system,” Sheppard says. The idea requested to Brown, who took Sheppard and Trujillo’s 2014 study down the halls of Caltech to astronomer Konstantin Batygin. Whereas Brown is more of an watchr of the night sky, Batygin is a theorist, someone who wants to comprehend why the cartography of the solar system is the way it is. “I consent presentant happiness in taking on observational baffles,” he says. “For me, the thrill is in putting the calculations out there and battle-testing them with data.”

Brown and Batygin ruminated on six ETNOs and accomprehendledged someskinnyg weird was going on. Unappreciate the eight comprehendn scheduleets, whose orbits are approximately circular and are oriented aprolonged the same flat schedulee, comprehendn as the ecliptic, these six objects—including Sedna—had elliptical orbits and were tilted about 20 degrees with admire to the ecliptic. The six also made their shutst approaches to the sun in the same region of space. They were all too far out to be wiskinny Neptune’s gravitational accomplish, but someskinnyg materializeed to have produceed their orbits.

Brown and Batygin’s computer models proposeed the only reasonable possibility was a hideed scheduleet with a mass five to 10 times that of Earth orbiting as far as 700 AU away. This world, perhaps one exiled from the hoter restricts of the solar system during its turbulent earlier years, regulated to cling to the sun’s gravitational ropes. And as it whirled thcdisorrowfulmireful the far depressedness, it wielded its own gravitational sway on those passing six orbs, herding them into analogous, strange new orbits.

Since Sedna’s discovery in 2004, the notion of a huge, incognito scheduleet had come up on disjoinal occasions. But Brown and Batygin’s 2016 paper announcing their calculations was a clarion call: We are self-promised that Planet Nine is out there. Now all we insist to do is discover it.

The hunt for a ignoreing scheduleet is inherently peculiar. “How many scheduleets are in the solar system?” Schwamb asks. “This should be an effortless ask, right? But it’s not!”

Finding a ninth scheduleet would be huge. Beyond consoling those in the disclose who still lament Pluto’s demotion, such a discovery could change what we comprehend about our solar system’s past. Any objects in, and beyond, the Kuiper belt are “relics left over after scheduleet createation,” Schwamb says. “They alert us about that hideed history that fundamentalpartner has been erased from the solar system.” Did scheduleets regulate to create that far from the sun, or did they migrate out there? Most orreries of scheduleets moving around other stars integrate a mini Neptune of some variety. “It is very odd that we don’t have one,” she says.

If it exists, Planet Nine is huge contrastd with Earth—Brown’s best guess is that it hovers around seven Earth masses. But it’s so far away that it’s beyond the discoverion capabilities of most telescopes. In vague, observatories have a choice: have a expansive field of see to see more of the night sky in one go or a huge mirror to accumulate more airy from a petiteer area and see far, faint objects. Space is rather expansive, so trying to zoom in on one minuscule patch of it in the hope of discovering a one object is innervously improbable to flourish.

Many astronomers—not fair Brown, Batygin, Sheppard and Trujillo—have tried seeing. Several more ETNOs have been set up, including the Goblin (discovered around Hapvalidateeen 2015), Farout and FarFarOut—more gravitational probes for Planet Nine hunters to study. But to date, Planet Nine itself has eluded them.

There is, of course, a chance that they can’t discover it not because Planet Nine is sneaky but because it doesn’t exist. Over the past decade various changenative hypotheses have sprung up to try to elucidate Sedna and its cohort’s weirdly clustered orbits.

One possibility is that there is a Planet Nine but not the canonical one; instead it’s someskinnyg ponderably punier—Mars-size—and it sits elsewhere on the solar system’s outermost boundary. In 2017 Kathryn Volk, an orbital vibrants researcher at the University of Arizona, thought the orbits of various trans-Neptunian objects hinted at the presence of a Mars-esque world wiskinny the Kuiper belt. Additional observational data on other far objects has since undercut her team’s hypothesis, and although the possibility of a Mars-appreciate Planet Nine has come up at astronomy conferences, Volk is now skeptical. “Much appreciate the more standard Planet Nine, they’re probably both wrong,” she says. “I don’t skinnyk any of the existing foreseeions are accurate.”

In 2020 scientists proposeed that an icy ring of primordial debris, if massive enough, could also be sculpting the orbits of disjoinal ETNOs. Brown notices that we see inclined frosty rings around other stars, but those rings are thought to be held in place by the gravitational sway of another hefty scheduleet, making this a more complicated exscheduleation than Planet Nine alone.

It’s also been proposeed that perhaps a passing star or a rogue scheduleet zipping thcdisorrowfulmireful space could have dragged Sedna and its friends onto their weird orbits prolonged ago. In 2019 researchers even wondered whether a minuscule bconciseage hole might be the culprit. When I elevate this possibility to Brown, he grins. “I have it!” he says. He fades for a moment, then reaelevates helderlying a sphere about the size of a volleyball. “This is a seven-Earth-mass bconciseage hole. One of my students 3D-printed it for me.”

Brown chuckles. “What we comprehend is that there is a seven-Earth-mass object out there. What it is, we don’t comprehend,” he says. “It could be a scheduleet. It could be a bconciseage hole. It could be a cat or a burrito. All of these are possibilities—some produce more sense than others.” He puts down his minuscule bconciseage hole. “A scheduleet is a repartner mundane exscheduleation.” After all, he says, we see scheduleets appreciate that on far orbits around other stars all the time.

Trujillo is a little more circumspect when pondering changenative exscheduleations. Sure, he says, they could be right; those theories deserve to be scrutinized. “We still don’t repartner comprehend how Sedna and the other ETNOs got out there,” he says. But the fact remains that “an undiscovered big scheduleet is a authentic possibility.”

Though not as adamant as Brown, Batygin is certainly bullish. In astrophysics, “most theories are wrong,” he says. “The most unforeseeed skinnyg I’ve come atraverseed over the course of the past eight years for this particular problem is that there hasn’t been a compelling other changenative.”

Arguably, the fantasticest dispute to the Planet Nine story is the proposeion that Sedna and company may not have strange orbits at all. Astronomers cannot see every region of space evidently. If an observatory is afflicted by horrible triumphter weather, then data will be conciseageing for that corner of the night sky. ETNOs also spend most of their unobesehomably prolonged orbits so far from Earth that they glint in sunairy only when they accomplish their shutst approach to the sun. Then there’s the Milky Way. Our solar system is perched on one of the arms of our spiral galaxy, and when we see inward, all we see is starairy. It’s pretty but irritatesome to astronomers. “Nobody discovers [trans-Neptunian objects] where the Milky Way is,” says Samantha Lawler, an astronomer at the University of Regina in Canada. “You’re seeing for a petite, fuzzy, moving dot, and when there are so many stars in the background, it’s difficulter to discover them.” Because astronomers comprehend about only a petite number of Kuiper belt objects and ETNOs, some scientists skeptical of the Planet Nine hypothesis skinnyk we spropose do not have enough proposeation to comprehend whether worlds appreciate Sedna repartner are on strange orbits or fair see appreciate they are for the moment.

“Each year we don’t discover [Planet Nine], the probability of it actupartner existing goes down theatricalpartner.” —Mario Jurić University of Washington

Think of it this way: envision you’re in the depressed, and you have a flashairy. You shine it on one patch of the floor ahead of you, and you see a handful of marbles in that one spot. (That’s Sedna and friends.) With that proposeation alone, you may skinnyk there must be a one-of-a-kind reason those marbles are in that spot. But there could be plenty of other marbles all over the floor—and if you could see all those other marbles, you would authenticize that the first seeming cluster of them isn’t a cluster at all. Instead it’s fair a random group of marbles on a floor covered in haphazardly placed marbles. The problem is that, for now, your flashairy isn’t radiant or expansive enough to let you see the rest of them.

This misperception is caused by what’s comprehendn as an observational bias. To see whether the case for Planet Nine was afflicted by one, Lawler and her colleagues turned to the Outer Solar System Origins Survey (OSSOS). Between 2013 and 2017, OSSOS used the Canada-France-Hawaii Telescope to scan eight patches of the night sky and ultimately identified more than 800 new Kuiper belt objects. Eight objects had unretagable distances from the sun fantasticer than 150 AU, making them ETNOs—the benevolents of objects that could be used as gravitational probes for Planet Nine. And their orbits were not clustered at all.

If a enormous hideed scheduleet is influencing these eight objects, they should show the same type of clustering as those being used to call upon Planet Nine. But they don’t. The OSSOS data cannot rule out Planet Nine, but they do propose that what may see appreciate clustered orbits sculpted by an inapparent world could, in fact, be an illusion. Authors of another bias-checking study, using the Dark Energy Survey, came to the same expansive conclusion in 2020. “Why say there’s someskinnyg more complicated if you can’t rule out the null result?” Lawler says. “That’s our argument.”

The crux of the argue is that we are dealing with petite-number statistics: there are too scant comprehendn trans-Neptunian objects for astronomers to validate one way or the other. “The agnostic perspective now is that we do not have enough data either way,” says Pedro Bernardinelli, an astronomer at the Institute for Data Intensive Research in Astrophysics and Cosmology at the University of Washington. “I am neutrpartner guaranteed that it’s probably not there. But I also skinnyk it’s silly to not search for it.”

Thankfilledy, that search is about to get a lot easier.

In May 2024 a cforfeitly 7,000-pound, car-size camera was shiftd from its produceion site in California to a mountaintop in Chile. After a 10-hour fairy and a disjoinal-day, triumphding, bumpy drive to an 8,700-foot-high peak in the Cerro Pachón mountain range, the 3,200-megapixel camera—the world’s bigst—get tod without a one scratch. Like the prize jewel for a monarch’s crown, the $168-million camera was then almost ready to be set in place wiskinny the cforfeitly finished Vera C. Rubin Observatory.

The observatory will see its first airy sometime in punctual 2025. Thanks to its enormous field of see, Rubin will consent images of the entire night sky seeable from the Southern Hemisphere night after night—and its house-size nest of mirrors will assemble up retagably far starairy, unbenevolenting cforfeitly everyskinnyg that shimmers or shifts about will be pboilingographed.

Rubin—a venture funded by the U.S. National Science Foundation and the Department of Energy—is named after the tardy, fantastic astronomer who, by seeing at the way stars and galaxies stuck together more than could be elucidateed by the gravity of apparent matter alone, uncovered compelling evidence for depressed matter. Her namesake is aptly set to discover a cornucopia of hideed objects, from faraway collapsing stars to millions of acarry outance increasers and even a bunch of intersalertar objects in our own solar system.

The Kuiper belt, whose population and set up are only unclpunctual comprehendn, stands to be fantasticly brightend by Rubin. After cforfeitly four decades of searching, astronomers have set up about 4,000 objects out there. “With Rubin, it should go up to about 40,000,” says Mario Jurić, an astronomer at the University of Washington. I transport that up with Brown, who chuckles. “Ah, who participates about those?” he says with a grin. But ultimately, he has his eyes on Planet Nine. And, he says, Rubin is probably going to discover it.

Here’s how: To satisfy Rubin’s myriad science objectives, astronomers are putting together a strategy for the observatory’s survey of the night sky, which will essentipartner be automated. Astronomers can’t fair ask for time on Rubin as they do on other telescopes. Instead algorithms will process Rubin’s nightly images to produce catalogs, which will then be freed to the community.

For solar system science, astronomers will see a enumerate of moving objects—those comprehendn and those previously unidentified—with orbital parameters based on the current crop of Rubin observations. Researchers seeking Planet Nine can then use the newly discovered trans-Neptunian objects to see whether the case for the scheduleet is stacking up or collapsing.

When lots of ETNOs have been set up, Brown says, it will become evident whether the clustered orbits one would foresee to be caused by a hideed scheduleet—appreciate those of Sedna and company—are current. And because Rubin will see the entire southern sky, any observational bias will be rapidly ruled out. “If the clustering is there, Planet Nine is there,” Brown says.

It’s also possible that among the moving objects Rubin discovers will be Planet Nine itself. If it’s more appreciate Uranus or Neptune—a hydrogen-enveloped orb with plenty of ice—it will mirror a lot of airy, making it easier to spot. (Even in that best-case scenario it would probably see appreciate a pinprick of airy in a Rubin image.) Pessimisticpartner, Batygin says, “it’s a naked rock”—­­a superdepressed world, pragmaticly inapparent. “Undeniably, that would suck. But that might be the truth of it. We’ll get what we’ll get, and we won’t get disturb. Well, some of us will get disturb.”

If it’s hanging out in front of the Milky Way, that would be “the nightmare scenario,” Bernardinelli says. “It will be very difficult to discover.” Jurić notices that Rubin’s gentleware will do its best to subtract that radiant conflagration of starairy, discneglecting, he hopes, anyskinnyg hideed wiskinny it. Will that toil? Jurić skinnyks so, “but you don’t comprehend until you try it,” he says.

Worst-case scenarios aside, astronomers foresee that the ignoreion to discover Planet Nine will be over in a scant years. In fair one, Earth (and Rubin) will have circled the sun once. Only inclement weather will impede us from seeing what’s out there; a horrible triumphter month may consent one month of filled-sky coverage away, but the telescope should be able to apprehend it the next year.

“Each year we don’t discover [Planet Nine], the probability of it actupartner existing goes down theatricalpartner,” Jurić says. And after a couple of years, the existence (or nonexistence) of Planet Nine will be, to most astronomers, unequivocal. Rubin is “the chooseimal scheduleet hunter,” Schwamb says. “I don’t skinnyk there’s any other telescope in the world that could regulate to do this.”

Most astronomers are satisfyed to defer and discover out what Rubin discneglects. Schwamb, whose Ph.D. proposer was none other than Mike Brown, treads participatefilledy. “I will be pleasantly excited if there is a scheduleet,” she says. “I will not be so surpelevated if there isn’t one.”

But Brown and Batygin have never been certainr. In a 2024 study, they checkd the orbits of 17 trans-Neptunian objects, each with a bizarre feature: their shutst approaches to the sun can get as cforfeit as Jupiter. Objects that traverse Neptune’s orbit appreciate that should get ejected from the solar system, so how can these objects on these orbits exist today? Someskinnyg is grabbing orbs that linger at the very edge of the solar system and putting them on orbits that consent them far shutr to the sun than they would otherteachd get, the scientists surmise.

Their study used virtual re-creations of the solar system and tried to see what benevolents of objects had the gravitational sway to sculpt these orbits—including passing stars, the Milky Way itself and Planet Nine. According to the researchers, the versions of truth without Planet Nine produce no sense. This outcome is “the mightyest statistical evidence yet that Planet Nine is repartner out there,” Batygin says.

If the scheduleet does exist, there’s a excellent chance that Brown and Batygin might not discover it first. Rubin may discover it autonomously, Jurić says, whereupon another group of astronomers reading the data will validate that it is genuine. Alternatively, Rubin’s gentleware might not discover it automaticpartner, but an astronomer may discover Planet Nine by using their own gentleware to go thcdisorrowfulmireful the imaging data or by perusing a enumerate of moving objects that Rubin set up but did not autonomously flag as Planet Nine honestates. Batygin, ever the theorist, says the discovery is what matters most, think aboutless of who claims it. “I fair want to comprehend the answer,” he says.

If Planet Nine is authentic, “my instant reaction might be relief,” Brown says. He accomprehendledges that should he not be the one to first cast eyes on it, he would experience an initial gut punch of frustration. “I would adore to discover it,” he says. But he’d be satisfied if he and his colleagues were showd right all aprolonged, and he met his daughter’s dispute of redemption—and he would be thrilled that the history of the solar system would change, once aget, partly because of his research.

“There’s a very excellent chance that we could be sitting around studying Planet Nine in fair a couple of years’ time,” he says. Every telescope, on Earth and in space, might be zeroing in on its secrets. Wantipathyver it’s appreciate, Brown says, “it will be the best scheduleet in the solar system.”