Planet Nine: Astronomers could discover elusive world within months

For years, scientists have observed the Solar System’s outer reaches in search of a Planet Nine.

While Pluto was demoted to dwarf planet status in 2006, some researchers believe an even larger world lurks beyond, waiting to be discovered.

After all, Uranus and Neptune were discovered much later than our closer planetary neighbors. There may be another planet out there; we don’t have the technology to spot it. But that could soon change.

“It is very possible that Planet Nine will be found within the first year of the Vera C. Rubin Observatory,” Caltech astronomer Mike Brown, one of the scientists who proposed the Planet Nine hypothesis, told Interesting Engineering in an interview.

With the Rubin Observatory starting in 2025, we could have a “new addition” to our Solar System surprisingly soon.

Why do scientists believe there is a Planet Nine?

If Planet Nine does exist, scientists believe it is billions of miles further away from the Sun than the known planets of our solar system.

Like dark matter, it has never been observed directly. But we know it might be there due to its gravitational impact on nearby objects.

In 2004, scientists observed that Sedna, a potential dwarf planet beyond the Kuiper Belt, had an unusual orbit around the Sun. This hinted that its orbit might be affected by another unknown object with a large mass in the outer solar system.

Then, in 2014, astronomers announced they had found a small object in the Kuiper Belt with an eccentric orbit. The discovery of the 2012 VP113 object lent weight to the Sedna hypothesis because Sedna and 2012 VP113 had similar orbits.

As Brown puts it, he and his colleague proposed the Planet Nine hypothesis after discovering that “the most distant objects in the Kuiper belt, on extremely elongated orbits that stay far away from Neptune, and everything else, are all clustered in one direction.”

Brown, who co-discovered Sedna, also looked at alternatives. “Some of our earlier hypotheses, before we realized that all of these objects were clustered, was that the highly elongated orbits that stayed far from Neptune were formed when a star came unusually close to the sun during the early history of the solar system.”

Ultimately, they believe some of the most distant known objects in our Solar System behave as though a large planet is influencing their orbit around the Sun. While humanity hasn’t discovered a planet since Neptune in 1846 – and the now-relegated Pluto in 1930 – that doesn’t definitively mean there is no other planet orbiting our star.

Could we finally observe Planet Nine next year?

Unlike dark matter, Brown believes we could directly observe Planet Nine very soon. The Vera C. Rubin Observatory in Chile is due to open in 2025. The groundbreaking new observatory took nine years to build and cost $1.9bn.

It will survey the night sky like never before. Crucially, for Brown and other Planet Nine proponents, it could finally find the elusive ninth planet. There is also the possibility it could rule it out altogether.

According to Brown, “it is very possible that Planet Nine will be found within the first year of Rubin. There’s always the chance it is just a little too faint for the observatory, but it is the best bet we have to date.”

While the James Webb Space Telescope has recently altered our perception of the early universe, Rubin will provide incredibly accurate data on objects closer to home.

Even though we have incredibly advanced space observatories like James Webb operating in space today, “space observatories are generally not designed to look over vast swaths of sky for faint objects,” Brown explained. “For that, we need telescopes on the ground.”

Rubin will map the night sky in unprecedented detail, and scientists say it will change our understanding of the universe. The ground observatory will use a laser pointer to accurately chart the night sky with its 8.4-meter diameter mirror and 3,200-megapixel camera.

Crucially, the observatory is designed to move constantly, meaning it can cover large areas relatively quickly. According to a report by The Guardian , it will be able to detect 10 million events per night, including supernova explosions and asteroids’ movements.

Planet Nine would alter our understanding of the cosmos

If Rubin does find Planet Nine, Brown said, “Our best guess is that it is like Neptune, but we could be totally wrong. It could even be a giant ice ball.”

One thing is for sure: The discovery of Planet Nine would have a massive impact on astronomy. If we do discover it, “we will suddenly have a fifth giant planet to study, in a mass range unique in the solar system,” Brown, who was also a key figure in Pluto’s demotion, explained.

The discovery of Planet Nine would undoubtedly result in agencies like NASA sending probes to the newly discovered world. Close-up observations would teach us a great deal about the Solar System’s past and about planets beyond our own system.

“Interestingly, the expected mass of Planet Nine—something like seven times the mass of the Earth—is one of the most common planetary masses in the rest of the galaxy,” Brown continued. “So we will finally have a chance to see one of these very common types of planets up close.”

If Planet Nine could be approximately seven times the mass of our planet, why have astronomers yet to spot it? One potential answer is that it is so far away that sunlight barely reaches the distant world. Another is that it doesn’t exist at all.

Not everyone believes in Planet Nine

While Brown and his team say they have discounted several different hypotheses that could account for the orbital irregularity of the Kuiper Belt objects, not all scientists are convinced.

For example, Samantha Lawler, an astronomer at the University of Regina in Canada, believes that the kinks in those orbits are down to “observational bias. “This is because it is easier to spot trans-Neptunian objects (TNOs) that are closer to the Sun than examples that are farther away on the outskirts of the Solar System.

Lawler was part of the Outer Solar System Origins Survey (OSSOS), a collaboration of 40 astronomers from eight countries who set out to discover and track Kuiper Belt objects (KBOs).

Over five years, they used the Canada-France-Hawaii Telescope to find 800 new KBOs. This almost doubled the number of known KBOs with well-measured orbits. Computer simulations based on these discoveries showed no clustering of KBO orbits.

In an article for The Conversation , Lawler wrote: “Many beautiful and surprising objects remain to be discovered in the mysterious outer solar system, but I don’t believe that Planet Nine is one of them.”

Still, Brown and his colleagues remain confident and undeterred. For his part, Brown sees the criticism of his hypothesis as a healthy example of the scientific process. “Scientists are, by nature, skeptical,” he said. “And for a large claim like this they are, appropriately, extra skeptical. In the end, we have to find it to make the most convincing case.”