For nearly a decade, astronomers have been scouring the outer reaches of the solar system for signs of a hypothetical ninth planet, to no avail. However, experts say we may finally be on the cusp of discovering it. Deep in the outer reaches of the solar system—so far from the known planets that the sun would barely be distinguishable from the nearest star—a vast, icy world may be lurking in the shadows, waiting to be discovered. More evidence has emerged of a hypothetical extra planet lurking in the farthest reaches of our solar system, and these clues lie in icy bodies that cross the orbit of Neptune on long, winding orbits around the sun.
Planet Nine, as it’s known, was first postulated in 2016 by Konstantin Batygin and Michael Brown of the California Institute of Technology; the latter also discovered the dwarf planet Eris in 2005. Their initial data focused primarily on the cluster of trans-Neptunian objects (TNOs), objects that spend most of their orbits farther from the Sun than Neptune. That’s quite far. Specifically, the duo studied highly inclined TNOs, objects orbiting the Sun at steep angles to the ecliptic plane.
An artist’s rendering of Planet Nine, a hypothetical world some scientists believe lurks undiscovered in the outer reaches of our solar system. R. Hurt/IPAC/Caltech
Since the Solar System’s contents formed from a disk around the Sun, one might expect the orbits of all objects orbiting the Sun to be relatively close to the plane of this disk. However, some objects do not, and the team suggests that this suggests that Planet Nine’s gravity may be pulling objects out of the ecliptic and grouping them into highly inclined orbits with shared “apses” (the closest and most distant points of their orbits around the Sun) and oriented at the same tilt relative to the ecliptic.
However, some astronomers were skeptical, arguing that what Batygin and Brown perceived as clustering was merely an illusion caused by observational error. The Caltech duo dispute this and published a paper in the spring of 2024 devoted to observations of low-inclination trans-Neptunian objects that do not cluster but still exhibit distinctive features.
These icy trans-Neptunian objects are unusual in that they spend most of their lives hundreds of times farther from the Sun than Earth, but their orbits are so elongated that they approach the Sun and briefly come closer than Neptune, which is only 30 times farther from the Sun than Earth. In this study, the scientists studied objects with long-period orbits that also actively interact with Neptune, particularly those that cross its orbit.
The existence of a Planet Nine with a mass roughly equal to Neptune’s could explain why several known extreme trans-Neptunian objects appear to be clustered in space. Diagram created with the WorldWide Telescope. Caltech/R.Hurt/IPAC
To be precise, this doesn’t apply to all Neptune-crossing objects. Pluto is a good counterexample. Like Pluto, the orbits of most trans-Neptunian objects are not as elliptical as those presented in the team’s new study. In fact, the trajectories of most trans-Neptunian objects allow them to remain close enough to Neptune for long periods of time to be controlled by the ice giant’s gravity.
However, the research team was only interested in those trans-Neptunian objects located hundreds of astronomical units from Neptune’s gravitational tides, where they could be influenced by Planet Nine, if it exists. Since these objects come from all directions close to the ecliptic plane and do not exhibit any cluster behavior, the same claim of bias raised against previous data on clustered trans-Neptunian objects with high inclinations is invalid.
The trans-Neptunian objects studied, like any other objects moving along similar trajectories, don’t spend much time in their orbits; over millions of years, the gravity of the azure-blue ice giant Neptune inevitably flings them around, scattering them over great distances and sometimes even ejecting them from the Solar System altogether. This means that whatever sends trans-Neptunian objects into Neptune-crossing orbits does so continuously. There must be a continuous process that ensures the replenishment of trans-Neptunian objects. This means the culprit can’t be an event that occurred in the distant past, such as a star passing too close. It must be something that still exists today.
There are two scenarios under which trans-Neptunian objects could regularly enter long, looping orbits that cross Neptune’s orbit. One involves the galactic tide—the gravitational force of the Milky Way surrounding us—acting on objects in the Oort Cloud, which lies far beyond Neptune. These objects are only vaguely affected by the Sun’s gravity due to their distance from our star, but the galactic tide could bring them closer to Neptune.
Another, perhaps more interesting, scenario is that Planet Nine’s gravity perturbs the Oort Cloud objects so much that they eventually move closer to Neptune.
Batygin and his team—Michael Brown, Alessandro Morbidelli of the Observatoire de la Côte d’Azur in Nice, France, and David Nesvorny of the Southwest Research Institute in Boulder, Colorado—ran two sets of simulations using observations of real low-inclination trans-Neptunian objects crossing the orbit of Neptune to determine which scenario is more accurate.
One model considered a planet five times the mass of Earth to influence the trans-Neptunian objects (the modeled properties used for Planet Nine were derived from characteristics that best explain previous data, such as a cluster of highly inclinated trans-Neptunian objects), while the other model omitted Planet Nine entirely and only simulated galactic tides. Which of these options would best address the problem of trans-Neptunian objects passing Neptune?
Simulations showed that low-inclination trans-Neptunian objects could regularly penetrate beyond Neptune’s orbit only if Planet Nine were actually there to “shoot” them. Galactic tidal vortices alone were calculated to be too weak to cause trans-Neptunian objects to pass past Neptune. Consequently, in the galactic tidal simulations, trans-Neptunian objects approach the Sun at a certain distance and then stay away from it. However, in the Planet Nine scenario, trans-Neptunian objects are distributed across a range of Neptune-crossing orbits, which is consistent with what we observe in reality.
There are officially eight planets in the solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. But in recent years, astronomers have speculated that somewhere in the far reaches of our cosmic neighborhood, a ninth world, evocatively nicknamed “Planet Nine,” may be lurking.
And no, we’re not talking about Pluto, which was demoted from full planet status to “dwarf planet” in 2006. Scientists believe Planet Nine is a gas or ice giant billions of kilometers distant from the other planets. If it exists, it could also reshape our understanding of the origin and evolution of the solar system.
Astronomers predicted how large this hypothetical world was, how far away it might be, and even where it would be in its orbit around the Sun. However, scientists failed to detect Planet Nine, sometimes called Planet X, for nearly a decade.
The unusual orbits of trans-Neptunian objects in and around the Kuiper Belt indicate that something massive is lurking in the outer Solar System. Getty Images
The idea of a ninth planet in the Solar System first arose after the discovery of Uranus in 1781 and Neptune in 1846, more than 3,000 years after the other planets were first discovered by the Babylonians. These discoveries proved that the Solar System was much larger than humanity had once believed and raised the possibility that other worlds await discovery.
But, aside from the now-demoted Pluto, no full-fledged planet has been discovered since then beyond Neptune or the Kuiper Belt—the giant ring of asteroids, comets, and dwarf planets orbiting the Sun beyond Neptune. And as astronomers mapped the outer solar system, it became increasingly unlikely that they had missed something as large as a planet.
However, a 2004 discovery changed the situation. Scientists discovered that Sedna, a potential dwarf planet located beyond the Kuiper Belt, orbited the Sun in an unusual orbit. Its unusual trajectory hinted that another large mass in the outer Solar System was exerting a gravitational pull on this mini-world. However, without additional information, this hypothesis was difficult to prove.
Then, in a 2014 study, astronomers announced the discovery of a smaller Kuiper Belt object, dubbed 2012 VP113, with an eccentric orbit similar to Sedna’s. The results also hinted that more eccentric trans-Neptunian objects (TNOs) have yet to be discovered.
These discoveries caught the attention of Brown and his colleague, Caltech astronomer Konstantin Batygin, who noticed that Sedna and 2012 VP113 shared a similar “bend” in their orbits. This shared irregularity, which causes the objects to briefly fall below the orbital plane of known planets, suggested that something—perhaps an asteroid cluster, a dwarf planet, or even a full-fledged world—was exerting gravity on these objects.
If Planet Nine is discovered, space agencies will likely send probes to this distant world. Anton Petrus
Since 2016, Brown, Batygin, and others have continued their search for Planet Nine. Although they have not yet found it, they have discovered even more unusual trans-Neptunian objects, bringing the total number to 13 and further strengthening the case for Planet Nine’s existence.
These discoveries also constrain Planet Nine’s potential size, its distance from the Sun, and its orbital path within the Solar System.
According to their most accurate estimates, this planet is approximately seven times more massive than Earth, or somewhere between five and ten times more massive than our planet. This would make it the fifth-most massive planet in the Solar System, after Jupiter, Saturn, Neptune, and Uranus.
Brown reported that Planet Nine’s composition is likely “most similar to Neptune’s” due to its distance from the Sun. This means its diameter is roughly twice that of Earth. Some scientists also speculate that Planet Nine may be surrounded by moons, similar to powerful gas giants.
If it exists, Planet Nine is likely located approximately 500 astronomical units from the Sun, or 500 times farther than Earth. This may seem incredible, but exoplanets of similar size have been discovered orbiting other stars at similarly vast distances, supporting this possibility.
At such a large distance, Planet Nine could take between 5,000 and 10,000 years to complete one orbit around the Sun. Its orbit is likely highly elliptical, so its distance from the Sun could vary significantly over time. Furthermore, its orbit is likely not in the same plane as the other planets, further complicating its detection.
Planet Nine’s unusual orbit and its extreme distance from the Sun also suggest it may be a rogue planet—an interstellar world captured by the Sun after it was ejected from its solar system. However, Brown and Batygin believe Planet Nine likely formed alongside the other planets in the Solar System.
See also... New method for observing individual atoms confirms century-old quantum mechanical theory |
Many astronomers are cautiously optimistic about the existence of Planet Nine.
Alessandro Morbidelli, an astronomer at the Côte d’Azur Observatory in France, told Live Science in an email that Planet Nine’s existence is “highly likely.” “There are several indirect lines of evidence for its existence,” added Morbidelli, who reviewed Brown and Batygin’s 2016 paper before its publication.
Scientists believe a ninth planet may be lurking somewhere in the far reaches of the solar system, and a new telescope may finally prove its existence. Nicholas Forder
David Rabinowitz, an astrophysicist at Yale University, agreed that something is likely out there, and that “Planet Nine” is “the best explanation at this point,” he told Live Science. The discoveries of new eccentric trans-Neptunian objects since the “Planet Nine” hypothesis was first proposed have bolstered confidence in the theory, he added.
“It’s been a real rollercoaster! I’ve gone from being 90% confident to being 10% or more,” Sean Raymond, a researcher at the Bordeaux Astrophysics Laboratory in France, told Live Science in an email. “I’m rooting for it to be true, but I’m still not sure I believe it.”
Doubts about Planet Nine stem from alternative possible explanations for the strange behavior of trans-Neptunian objects. For example, the gravitational anomalies noted by Brown and Batygin could be caused by a young black hole, an unseen giant dust disk, or a historical close encounter with a rogue planet. Furthermore, trans-Neptunian objects may indicate a need to adjust our model of gravity.
Others believe the apparent kinks in TNOs are simply “observational error,” since it’s easier to spot TNOs that are closer to Earth than more distant ones, Samantha Lawler, an astronomer at the University of Regina in Canada and a prominent critic of the “Planet Nine” hypothesis, told Live Science in an email.
“I think there are still a lot of really interesting bodies in the outer solar system that have yet to be discovered,” Lawler said. But Planet Nine isn’t one of them, she added.
However, Brown and Batygin disagree that observational error creates the illusion of the existence of a ninth planet.
“I’m as sure as you are that Planet Nine exists until you find it,” Brown said.
So, if Planet Nine exists, why haven’t we discovered it yet? The short answer is that the hidden planet is “very, very far away,” Brown said. The light reflected from the planet would be very dim by the time it passes most of the solar system (twice), making it virtually impossible to observe.
Initially, the researchers also had no idea where the planet was located in its proposed orbit. This meant they had to scan a vast area of the sky to find this faint body—a bit like trying to “find a single white whale in the ocean,” Brown said.
According to Brown, the researchers have now analyzed thousands of images from multiple sky surveys along Planet Nine’s projected orbital path, looking for objects that move over time.
Unfortunately, the night sky is teeming with bright moving objects like comets, so researchers have to sift through “a lot of junk” to find the planet, Brown added.
In their latest paper, Brown and Batygin analyzed data from the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) at the Haleakala Observatory in Hawaii and confidently ruled out about 78% of the proposed orbital path as possible harbour sites.
Comment on Facebook* The owner of the Meta company is recognized as extremist in Russia and is banned.See also... Complete list of HTML/Javascript event handlers with examples List of required documents for a website in the Russian Federation |
