There Could Be Hundreds of Undiscovered Planets in Our Own Solar System

Astronomers have discovered planets that are light years away, so you’d think that we’d pretty much be done exploring our solar system. Turns out that’s not the case: Researchers have just announced the discovery of a new dwarf planet far beyond Pluto’s orbit in a find that suggests there may be many more planets that orbit the sun.

The object, called 2012 VP113 but nicknamed “Biden” for now, has a diameter of 450 kilometers, so it’s about a fourth the size of Pluto. Though it’ll get an official name sometime in the next couple years, it won’t be seen hanging from elementary school solar system mobile models anytime soon. But other, yet-to-be-discovered planets might be. The mere existence of Biden means there may be hundreds of similar objects, some of which could be as large as 10 times the size of Earth, according to Scott Sheppard, author of a study describing Biden in Nature.

That’s because Biden exists in a part of the solar system known as the inner Oort cloud, an area that has long been known about but was expected to be a completely empty “no-man’s land.” The inner Oort cloud is about 80 times further away from the sun than the Earth is and situated in a spot that's likely both too close to the sun for objects to merely float away but too far from other stars to be pulled into their orbit.

Sheppard says it’s a complete mystery as to how Biden ended up there, but he has some theories: A “rogue planet” may have once been put out there somehow and pulled other objects with it, a “stellar encounter” could have happened where a passing star came so close to our solar system that it was able to pull objects to the area, or, during the sun’s formation, material could have been ejected out there. In any case, what was once considered empty space now appears to be quite full, a hypothesis made based on the forces interacting on Biden.

“We expect we’d find 5,000 more objects or so like the one we found, and 1,000 of them would be more than a thousand kilometers in size. We’re pretty sure objects far bigger than Pluto and something as big as Mars or the Earth is there,” he told me. “If we found something like that, it would basically become another planet in our solar system. Most people say we have eight planets and a bunch of dwarf planets. Well, something of that mass and size would definitely have to be added to our main planet system.”

That’s the next task on the list for Sheppard and his team at Carnegie’s Las Campanas Observatory, based in the Atacama Desert in Chile. Biden is the first discovery from that new telescope, and Sheppard expects the team will begin finding similar objects soon (he says the team has already found objects the same size as Biden, but isn’t ready to publish the results yet.”)

So why, if we’re able to discover planets hundreds of light years away, haven’t we found these objects before now? It’s because a completely different technique has to be used to find objects within our solar system.

“When you’re inside the solar system, it’s like you’re in a forest looking out. If you’re standing in the forest there’s trees everywhere and you can’t see everything,” he said.

When telescopes like Kepler are looking for exoplanets, it looks for the shadow cast upon any given star as a planet completes its orbit. From there, scientists can estimate its size with ease. Not so in the solar system. To detect a new planet, it basically has to be directly observed, which can only be done with reflected sunlight so far.

“It gets very faint very fast out there because the light has to travel so far,” he said. “It’s not an efficient way of doing it, but it’s the only way we can detect them.”

Biden, like any other planet found that far out, would likely be very different from any of the “standard” planets. All of the planets we know about so far are on a similar, “flat” orbit around the sun, while Biden has a severe, 25-degree inclined orbit. Anything else found out there would probably have a similarly inclined orbit, which can make it more difficult to detect in the first place. In any case, the new telescope is helping us. Biden was discovered while the telescope was surveying a very small patch of the night sky, and there’s still plenty of places to keep looking.

“We’re expecting to find some very big objects,” he said. So far, a small one has already fundamentally changed what we know about our solar system.