A curious orbital pattern among objects in the Kuiper Belt points to the presence of a hidden planet at the very edge of the solar system, too far for us to detect but large enough to exert strong gravitational effects on surrounding celestial bodies.
It’s becoming increasingly apparent that we barely know our solar system at all. It used to be so simple: sun, nine planets, asteroid belt, a few hundred moons here and there… But now things are much less certain. Pluto’s classification has been hotly contested ever since its controversial demotion to dwarf planet status in 2006. And most people don’t even know that we have another belt of objects beyond Pluto called the Kuiper Belt, full of surprisingly large chunks of ice and rock. Now, it turns out we may have yet another planet drifting even farther afield.
Astronomers suspect the presence of a tenth planet based on the orbital patterns of several Pluto-sized objects beyond the Kuiper Belt. The expanding scope of space exploration has revealed many new dwarf planets lying in the far recesses of the solar system — the discovery of Eris, a dwarf planet even larger than Pluto, was responsible for its demotion. But all these objects follow a strangely similar orbit that doesn’t make sense considering their distance from any other known planets.
A 2014 paper published in Nature first described the inexplicable synchronization of 12 objects in the Kuiper Belt, including a new dwarf planet nicknamed “Biden.” These objects move in accord with Sedna, a dwarf planet discovered in 2003 whose origin stumped astronomers. The authors are now preparing another paper detailing the discoveries of even more objects with nonrandom orbits. All of these planetesimals, or miniature planet-like objects, swing through orbits that bring them from around 80 AU (astronomical units) from the sun at their closest points to approximately 900 AU at their farthest points. They follow these extremely lopsided orbits with startling fidelity.
This mounting evidence has convinced a few astronomers that there must be something huge hiding far beyond our detectable reach that is responsible for these abnormally normal orbits. Scott Sheppard, one of the authors of the 2014 study, explained to the Washington Post that a sufficiently massive planet would disrupt and randomize the orbits of smaller bodies, and the objects of their study are moving in sync because they’re all trying to avoid the perturber.
In order to shepherd so many miniature planets, this perturber must be massive enough to generate a strong gravitational field — potentially four times as large as Earth. In fact, it could be similar to the rocky cores at the center of gas giants like Jupiter and Saturn. But it’s also at least 200 times farther from the sun than we are, which explains why it barely reflects any sunlight and remains obscure to us.
Advances in imaging technology will hopefully illuminate more of these mysteries and confirm whether or not we’ve been ignoring another planet all this time. Far-reaching missions like NASA’s New Horizons will also expand our comprehension of the cosmos. But before we venture out beyond the Kuiper Belt, there’s still so much we have yet to understand about our own solar system.