An as-yet-unseen planet may be lurking at the very distant edge of our solar system, or it might not exist at all. That incredibly vague and unsatisfying idea is the sum total of what scientists have been able to tell us about the mysterious “Planet Nine,” and it doesn’t look like we’re getting any closer to actually solving the riddle.
In a new research paper published in the Astronomical Journal, astronomers from multiple universities propose a new explanation for the bizarre behavior of distant solar system objects that seem to have been affected by the gravitational pull of a planet nobody has ever seen.
Planet Nine — no, Pluto still isn’t a planet, we’re talking about a different one here — has never been seen, but by observing the orbits of some very distant objects in our solar system, it seems like something very large is tugging on them, pointing to the existence of a world humans have never laid eyes on.
“We wanted to see whether there could be another, less dramatic and perhaps more natural, cause for the unusual orbits we see in some [objects],” Antranik Sefilian, co-author of the research, said in a statement. “We thought, rather than allowing for a ninth planet, and then worry about its formation and unusual orbit, why not simply account for the gravity of small objects constituting a disc beyond the orbit of Neptune and see what it does for us?”
Instead of a model that included one large planet doing the gravitational pulling, the team calculated the potential of a scattering of much smaller but more abundant objects spread across a large area. As it turns out, the collective pull of these smaller objects does the same job as a single large planet would, and would seem to be a more plausible explanation than a missing planet.
If a debris disc is responsible for the odd behavior of some distant objects in our system, it would be difficult to tell from our vantage point, since we’re observing things from the inside. “The problem is when you’re observing the disc from inside the system, it’s almost impossible to see the whole thing at once,” Sefilian notes. “While we don’t have direct observational evidence for the disc, neither do we have it for Planet Nine, which is why we’re investigating other possibilities.”