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Planet 9 location, orbit, distance, name, and black hole theory for the mysterious Solar System object

Astronomers are hot on the hunt for a giant planet in our outer Solar System. If it actually exists, that is.

Our Solar System may be a lot more complicated than it looks. For the last few years, astronomers have been searching for — and debating the existence of — Planet Nine, a giant planet orbiting somewhere far beyond Pluto and exerting an unseen influence on the orbits of smaller objects in the outer Solar System.

While the several dwarf planets seem to point toward this unseen, larger-than-Earth object, it has eluded astronomers thus far. And not all of them take it as a matter of time — several astronomers think that it may just be a sampling bias that may not be as weird as it seems.

Here’s everything you need to know about the possible lost sibling of the solar system, from the basic theory to where it may be located, its orbit, and more.

What is Planet 9?

Planet Nine is a hypothetical giant planet that might be orbiting the Sun somewhere beyond Pluto. Its presence is one possible explanation for the weird way a handful of small icy objects in the outskirts of the solar system seem to cluster into very similar orbits. These objects are all in the Kuiper Belt, the same region of the Solar System that contains Pluto.

These objects — including the dwarf planet Sedna — all loop around the Sun in long, narrow elliptical orbits. They’re all tilted at about the same slight angle relative to most of the Solar System, and they all make their closest pass to the Sun in roughly the same sector of the Solar System. It looks as if these small objects’ orbits are stretched and tilted by the gravity of something much bigger: an unseen planet.

These objects are believed to have been flung into their weird orbits by Planet Nine. Caltech

In 2016, Caltech astronomers Michael Brown and Konstantin Batygin published the results of their computer models, which suggested that a planet about the mass of Neptune, orbiting unseen about 20 times further from the Sun than Neptune, could provide the gravitational nudge that explains the cluster of small Kuiper Belt objects.

Some astronomers have been hunting for Planet Nine ever since, while others have fiercely debated whether the unseen giant planet exists.

Has Planet 9 been found?

No, Planet Nine has not been observed as of this moment.

How far away is Planet 9?

If Planet Nine exists, it’s out in the cold, dark fringes of our Solar System.

Batygin and Brown’s models say that Planet Nine should be, on average, about 20 times further from the Sun than Neptune. For comparison, our little blue planet averages 93 million miles away from the Sun, while Neptune orbits at a distance of about 2.8 billion miles, where the Sun is much dimmer and appears only about 3.3 percent of its size in our sky.

Planet Nine’s average distance from the Sun should be about 56 billion miles away. At that distance, the Sun would look like just another star in the perpetually dark sky.

However, a study published in September 2021 suggests that Planet Nine may be closer to the Sun than the original models predicted — though it’s still way out at 10 times the distance of the Sun to Neptune and 380 times the distance of the distance the Sun to Earth.

Michael Brown and Konstantin Batygin, the astronomers who proposed Planet Nine. The Washington Post/The Washington Post/Getty Images

How big is Planet 9?

According to Batygin and Brown’s models, it would take an object with about as much mass as Neptune to stretch and tilt the orbits of Sedna and the other clustered Kuiper Belt objects. That means Planet Nine is about 10 times as massive as Earth. If that’s the correct mass, it’s a little smaller than Neptune or Uranus.

So far, the most likely origin story for Planet Nine is that it formed in about the same area of space as the other giant planets, then got ejected by the gravity of its neighbors during planetary migration.

What is Planet 9’s orbit?

The computer models that originally predicted Planet Nine’s existence also modeled its orbit, which is probably a very long, thin ellipsis. Even at its closest approach to the Sun, it remains much further away than Pluto. At an average distance of about 56 billion miles away, it would take Planet Nine between 10,000 and 20,000 Earth years just to complete one trip around the Sun.

Is Planet 9 a black hole?

A group of astronomers, including Avi Loeb at Harvard University, suggested Planet Nine may be a tiny black hole somewhere out in the Oort Cloud.

If Planet Nine turns out to be Black Hole Nine instead, it’s probably about the size of a grapefruit but about 5 to 10 times the mass of Earth. Black holes, by definition, are so dense that even light can’t escape their gravity, so the only way to find one would be to spot the flashes of radiation released when a hapless comet crosses the event horizon of the black hole.

That’s precisely what Loeb and his colleagues are planning to do with data from the Vera Rubin Observatory’s decade-long sky survey, Legacy of Space and Time, which will start in 2023. Meanwhile, other astronomers will be using Rubin’s data to look for previously unseen objects in the outer solar system. Time — and evidence — will tell us who’s right.

Will we be able to get Planet 9 photos?

If Planet Nine exists, astronomers hope to collect images of it sometime in the next ten to fifteen years, but you shouldn’t expect those images to be visually stunning. Because the hypothetical planet might be about 56 billion miles away, it doesn’t receive much light from the Sun, and it reflects very little light toward Earth. The first images of Planet Nine are likely to be a few pixels on a dark background.

Future missions may eventually be able to reveal more detail about the long-lost planet, but astronomers will have to find it first.

If Planet Nine is out there, it may be smaller and harder to find than Neptune, the last discovery of a large planet in our Solar System, also predicted by mathematics before it was found.Freelanceimages/Collection Mix: Subjects/Getty Images

What will Planet 9 be named?

Astronomers have been hunting “Planet Nine” or “Planet X” for the last five years, but when it stops being a hypothesis and becomes an actual planet, it will get a new name.

The honor of naming a new planet goes to the person, or the team, who actually makes the discovery, which means Planet Nine’s leading proponents, Brown and Batygin, may or may not get to name it. And whoever does get to name the first new major planet discovery in 200 years will have to get the approval of a group called the International Astronomical Union before the moniker becomes official.

Traditionally, large planets in our Solar System have been named for Roman deities; our homeworld is an exception since “Earth” comes from an Old English word meaning simply “ground.”

In the last few years, however, astronomers have started naming objects in the Kuiper Belt for Indigenous deities from around the world. Sedna is named for an Inuit sea goddess, and other distant, tiny worlds are named for Haumea, a Hawai'ian goddess of childbirth, and Makemake, a Rapanui creator god, just as a couple of examples.

When will Planet 9 be found?

If there’s a giant planet lurking around the outskirts of our Solar System, astronomers will probably find evidence of it in the next 10 to 15 years.

The next generation of telescopes, both in orbit and here on Earth, may increase astronomers’ chances of finding Planet Nine. For instance, the Vera Rubin Observatory, which will begin its decade-long sky survey in 2023, should be capable of detecting the dim, distant planet. NASA’s much-delayed James Webb Space Telescope could offer another possibility when it launches and begins observations.

It’s also possible that the first images of Planet Nine have already been captured. Several teams of astronomers are searching archives of data from NASA’s WISE and NEOWISE missions, PAN-STARRS, and the Catalina Sky Survey. According to astrophysicist Scott Tremaine, evidence may also turn up in data from the European Space Agency’s Gaia star-mapping mission if the unseen planet’s gravity bends the light from stars in the background.

So far, no one has spotted a previously unknown planet in the data, but Batygin, Brown, and others say that by ruling out large swaths of the sky, they’re narrowing down the search.

Does Planet 9 exist?

That’s a question that can only be answered by either finding Planet Nine or searching enough of the outer Solar System to rule it out.

Some astronomers are skeptical, however. One key argument against the Planet Nine hypothesis claims that Batygin, Brown, and other proponents see a pattern — the clustered orbits of Sedna and friends — that’s not really there. Because we’ve mapped the orbits of so few objects in the outer Solar System, Planet Nine critics say, the small sample can seem to show a pattern that would fade into the background of a more extensive set of data.

According to a study published in September 2021, however, even when researchers accounted for the small sample size, the cluster of similar orbits still stood out. According to the study's authors, there’s about a 0.4 percent chance of that pattern happening randomly.

For the moment, Planet Nine is just an idea proposed to explain that pattern. It’s in good company, though — 200 years ago, astronomers similarly discovered Neptune. Astronomers John Couch Adams and Urbain Le Verrier independently noticed that some significant, unseen source of gravity seemed to be affecting Uranus’ orbit. They started looking and eventually found Planet Eight.

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