For nearly ten years, astronomers have searched the outer solar system for evidence of a potential ninth planet, but to no avail. But according to scientists, we might finally be close to discovering it.
There might be a huge, frozen globe hiding in the shadows, just waiting for humanity to find it. It would be so far from the known planets in the outer reaches of the solar system that the sun would hardly be able to be distinguished from a neighboring star.
And with the help of a cutting-edge telescope that will start looking at the sky next year, the day that we ultimately locate this elusive planet might not be far off.
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune are the eight recognized planets in the solar system. However, astronomers have recently suggested that a ninth globe, dubbed “Planet Nine,” might be lurking in the distant corners of our cosmic neighborhood.
No, we’re not referring to Pluto, which was downgraded to a “dwarf planet” in 2006 from full planetary status. Rather, Planet Nine is thought to be a gas or ice giant that is billions of kilometers away from the other planets. It might also change how we think about the beginnings and development of the solar system if it is real.
The size, distance, and even the proper location of this hypothetical world in its orbit around the sun have all been predicted by astronomers. However, for almost ten years, scientists have been unable to locate Planet Nine, also known as Planet X.
However, the search for the ninth planet in the solar system might soon be over. Experts told Live Science that with the revolutionary Vera C. Rubin Observatory debuting in 2025, we might either discover Planet Nine in the coming years or definitively rule it out.
“It’s really difficult to explain the solar system without Planet Nine,” Caltech astronomer Mike Brown, who co-developed the Planet Nine theory with a colleague, told Live Science. “But there’s no way to be 100% sure [it exists] until you see it.”
The theory of Planet Nine
The discoveries of Uranus in 1781 and Neptune in 1846, more than 3,000 years after the Babylonians first observed the other planets, planted the seeds for the notion that there might be a ninth planet in the solar system. These findings suggested that there might be more worlds out there just waiting to be found and demonstrated that the solar system was far broader than previously believed.
However, since then, neither the Kuiper Belt—a vast ring of asteroids, comets, and dwarf planets that circle the sun beyond Neptune—nor any full-fledged planets beyond Neptune have emerged, with the exception of the now-defunct Pluto. Furthermore, it appeared less likely that astronomers were overlooking anything as massive as a planet as they charted more of the outer solar system.
But that was altered by a finding made in 2004. Researchers discovered that the orbit of Sedna, a possible dwarf planet outside the Kuiper Belt, was peculiar. Its peculiar course suggested that the mini-world was being pulled by the gravitational attraction of another massive mass in the outer solar system. However, this idea proved difficult to confirm in the absence of more facts.
Astronomers then reported in a 2014 study that they had found a smaller object in the Kuiper Belt with an eccentric orbit resembling Sedna’s, called 2012 VP113. Additionally, the results suggested that there were more eccentric trans-Neptunian objects (TNOs) out there.
When Brown and fellow Caltech astronomer Konstantin Batygin realized that Sedna and 2012 VP113 had the same “kink” in their orbits, they became interested in these results. An asteroid clump, a dwarf planet, or perhaps a full-fledged world could have been pulling on these objects, as evidenced by this common irregularity that causes the objects to momentarily dip below the plane of orbit of the known planets.
Researchers have been able to piece together the Planet Nine puzzle with the help of the eccentric TNOs’ orbits. (Photo courtesy of JPL-CaltechR. Hurt)
Brown, who also co-discovered Sedna and played a key role in Pluto’s planetary demotion, told Live Science, “At the beginning, we didn’t say there was a planet because we thought that was a ridiculous thing for there to be.” “But we tried a lot of different things to explain what we were seeing, and nothing else worked.”
The two chose to postpone their results until they could come up with a less contentious explanation, even after realizing that a ninth planet might exist. The discovery of four additional TNOs with correspondingly asymmetrical orbits, however, abruptly made a missing planet appear to be the most plausible explanation.
The pair estimated at the time that the odds of all six TNOs they had examined sharing their orbital peculiarities by accident were only 2%. “And as soon as you see that, you’re like, ‘Oh crap, there’s a planet there,'” said Brown.
Thus, the “Planet Nine hypothesis,” which Brown and Batygin published in 2016, has captivated the public’s interest ever since.
Closing the gaps
Brown, Batygin, and others have been searching for Planet Nine since 2016. Even though they haven’t found it yet, they have located more oddball TNOs, increasing the total to 13 and supporting the idea that Planet Nine exists.
The possible size of Planet Nine, its separation from the sun, and its orbital path through the solar system are all limited by these findings.
According to Brown, “our best estimates are that it’s about seven times more massive than Earth,” which is equivalent to five to ten times the mass of our planet. He went on to say that this would place it fifth in the solar system in terms of mass behind Jupiter, Saturn, Neptune, and Uranus.
Because of its distance from the sun, Planet Nine’s composition is most likely “most like Neptune,” according to Brown. “That would put its diameter at something like two times the width of Earth,” he stated. Additionally, some scientists have proposed that, like the large gas giants, Planet Nine may have moons surrounding it.
If Planet Nine exists, it is probably 500 astronomical units from the sun on average, which is 500 times farther away than Earth. This may seem far-fetched, yet it is feasible because exoplanets of comparable sizes have been found orbiting extraterrestrial stars at similarly great distances.
At this distance, a single orbit of the sun may take Planet Nine anywhere from 5,000 to 10,000 years. Its distance from the sun would fluctuate greatly over time because of its likely very elliptical orbit. It is considerably more difficult to locate because it probably does not revolve on the same plane as the other planets.
The hypothesis that Planet Nine is a rogue planet—an intergalactic globe that was grabbed by the sun after being expelled from its star system—is further supported by its peculiar orbit and great distance from the sun. However according to Brown and Batygin, Planet Nine most likely formed in the solar system along with the other planets.
Planet Nine is probably composed similarly to Uranus (left) and Neptune (right), depending on how far away it is from the sun. (Photo courtesy of Getty Images) ))
Does it Actually exist?
The existence of Planet Nine is viewed with cautious optimism by many astronomers.
Alessandro Morbidelli, an astronomer at the Côte d’Azur Observatory in France, told Live Science via email that it is “quite likely” that Planet Nine exists. “There are several indirect lines of evidence in favor of its existence,” Morbidelli, who was a reviewer of the 2016 work by Brown and Batygin, stated.
Yale University astrophysicist David Rabinowitz concurred that something is probably out there and that Planet Nine is “the best explanation so far,” he told Live Science. “Confidence in this theory has been maintained by the discovery of other eccentric TNOs since Planet Nine was first proposed,” he said.
However, not everyone believes in the existence of Planet Nine.
“It’s been quite the journey! In an email to Live Science, researcher Sean Raymond of the Bordeaux Astrophysics Laboratory in France said, “I’ve gone from thinking it was 90% there to 10% and all around.” “I’m rooting for it to be there, but I’m still agnostic on whether I believe it’s there.”
Doubts about Planet Nine are based on other potential explanations for the strange behavior seen among TNOs. For instance, Brown and Batygin found gravitational anomalies that might be caused by a nascent black hole, an undetectable large ring of dust, or a previous close encounter with a rogue planet. However, the TNOs may suggest that our gravity model needs to be adjusted.
Some believe the apparent TNO kinks are simply a “observational bias,” as it is easier to detect TNOs that are closer to Earth than those that are farther away, said Samantha Lawler, an astronomer at the University of Regina in Canada and a prominent critic of the Planet Nine theory, in an email to Live Science.
“I believe that there are a lot of really interesting bodies left to discover in the outer solar system,” Lawler stated. However, she continued, Planet Nine is not one of them.
Brown and Batygin, however, reject the idea that the appearance of a ninth planet is due to observational bias.
“I am as confident as you can possibly be [that Planet Nine exists] until you actually find it,” Brown stated.
How come we haven’t located it?
Why haven’t we discovered Planet Nine yet, if it exists?
According to Brown, the undiscovered planet is “very, very far away,” to put it succinctly. By the time it went twice across the majority of the solar system, light reflected off the planet would be extremely dim, making it nearly impossible to observe.
At first, the scientists were likewise clueless about the planet’s location along its anticipated orbit. To detect this faint body, they have had to search a vast area of the sky, which is like attempting “to find a single white whale in an ocean,” according to Brown.
In order to find things that change over time, scientists have examined hundreds of photos from various sky surveys along Planet Nine’s suggested orbital route, according to Brown.
Data from the Pan-STARRS-1 observatory in Hawaii has already narrowed down where Planet Nine may be hiding. (Image credit: Rob Ratkowski / Harvard Center for Astrophysics)
The researchers must, however, sift through “a lot of garbage” in order to locate the planet because the night sky is crowded with bright, moving objects, including comets, Brown continued.
In their most recent study, Brown and Batygin confidently ruled out about 78% of the predicted orbital track as potential hiding spots for the planet after analyzing data from the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) at Haleakala Observatory in Hawaii.
As a result, the location of Planet Nine was reduced to somewhere in the outermost 22% of its orbital path. Unfortunately, this space cannot be adequately searched by telescopes like Pan-STARRS due to its lack of power.
When are we going to locate it?
We will need a telescope strong enough to detect Planet Nine if it is concealed in the furthest limits of its orbit.
With a higher likelihood of locating the planet than Pan-STARRS, Brown, and Batygin have already started examining data from Japan’s Subaru Telescope in Hawaii. However, scientists will look to the next Vera C. Rubin Observatory, which is presently being built in Chile, if this survey is unable to finish the task.
Similar to how the James Webb Space Telescope has allowed researchers to look farther across the observable universe than ever before, this ground-based telescope, which will be outfitted with the largest digital camera in the world, will allow researchers to look deeper into the solar system than any of its predecessors.
According to Brown, Planet Nine might be discovered in the next two years with the use of the cutting-edge telescope. But he also made a joke about how, since 2016, he has been repeating the same thing every year.
Within a year of the Rubin Observatory going online, Raymond and Rabinowitz both agreed that Planet Nine could be located. But if the planet is not discovered by the telescope in the first few years, “then the hypothesis is pretty much dead,” Raymond stated.
However, Morbidelli and Rabinowitz noted that even if the telescope is unable to locate the planet right away, it may still detect further TNOs, which would demonstrate the viability of the proposal.
Space organizations will probably deploy probes to visit the far-off planet if Planet Nine is found. (Photo courtesy of Getty ImagesAnton Petrus))
While there is still disagreement among scientists on the existence of Planet Nine, they all concur that the most significant solar system discovery of the century would probably be the actual discovery of the elusive world.
Raymond described it as a “remarkable” discovery. Additionally, he said, it would be “huge” for our knowledge of the origins and evolution of the solar system.
According to Morbidelli, studying the planet may also help us understand how huge planets grow and change over time. In addition to providing additional information about solar system planets, this would reveal thousands of massive exoplanets orbiting far-off stars.
More hints about the solar system’s history may also be revealed if space organizations like NASA deploy probes to fly near the planet.
“It’ll have many secrets that will be unlocked by studying it in detail,” Brown stated.