Before the doomsayers hijacked "Planet X" and used it as a phantom (a.k.a. "Nibiru") to scare people into believing the 2012 doomsday hype, the hunt for Planet X was an exciting astronomical quest to find a hypothetical world in the outermost reaches of the solar system in the early 20th century.
Although dwarf planet Pluto was discovered during the search for Planet X in 1930, apparently ending the quest, there is enduring evidence for the existence of a substantial planet gravitationally shaping the population of minor bodies in the Kuiper belt and beyond. The only problem is, we can't see it.
Earlier this month, at a meeting of the American Astronomical Society in Timberline Lodge, Ore., Rodney Gomes, an astronomer from the National Observatory of Brazil in Rio de Janeiro, announced the results of his simulation of a region beyond Pluto known as the "scattered disk," suggesting the presence of an as yet to be discovered massive world.
The scattered disk is a sparsely populated region that overlaps with the Kuiper belt at around 30 AU (Neptune's orbit), and some scattered disk objects (or SDOs) have extreme orbits that extend to 100 AU.
One such small world is Sedna, a dwarf planet with a highly elongated orbit. "Sedna's orbit is truly peculiar," said Caltech planetary scientist Mike Brown, who led the team that discovered Sedna in 2003.
These extreme orbits, argues Gomes, could be due to the presence of an unknown massive planet. By his reckoning, a planet four times the size of Earth may be out there beyond the orbit of Pluto. In his simulation, he placed the gravitational field of a large planet and watched the effect it had on the SDO's orbits.
"Rodney Gomes is actively seeking further evidence, and I await his findings with interest!" Douglas Hamilton, an astronomer at the University of Maryland, told Life's Little Mysteries. "He has taken on a difficult task, but is taking the right approach. It is definitely a high-risk, high-reward, situation - a discovery of a new planet would be spectacular!"
Although the presence of a massive planet may explain the extreme orbits, there is little else that suggests Planet X 2.0 really is out there. But the method of seeking out other worlds while looking for their gravitational influence on the orbits of other celestial bodies has been done before, with historic success.
In 1781, British astronomer Sir William Herschel noticed a perturbation in Uranus' orbit. By 1821, French astronomer Alexis Bouvard surmised that Uranus was being slightly "tugged" by the gravity of another, as yet to be discovered, massive planet in the outer solar system. In the 1840s, English and French astronomers John Couch Adams and Urbain Le Verrier independently went on to calculate where this mystery planet should be in the night sky by purely measuring these little deviations in Uranus' path.
Fifty-five years after Herschel noticed Uranus' perturbations, the distant planet was officially discovered by German astronomer Johann Galle in the location predicted by Couch Adams and Le Verrier. It was named Neptune.
Following the discovery of Neptune through studying perturbations in the orbit of Uranus, astronomers in the late 19th century still believed there must be another massive planet in the outer solar system causing additional perturbations to Uranus. By 1906, Percival Lowell - founder of the Lowell Observatory in Flagstaff, Ariz. - was inspired by these hints of another world and started a search for what he dubbed "Planet X."
It wasn't until 1930 that Clyde Tombaugh, an astronomer at Lowell Observatory, discovered Pluto. At the time, it was thought the search for Planet X had come to an end, but after follow-up observations in the decades after Pluto's discovery, the tiny world was found to have a minuscule gravitational field - it wasn't the "Planet X" astronomers were looking for.
As it turned out, many of the perturbation measurements were eventually put down to observational error, but that didn't negate the potential for more large planets beyond our observational capabilities existing beyond the Kuiper belt - the scenario that Gomes is currently investigating.
This new search for a hypothetical world is interesting, and reminiscent of Lowell's hunt for Planet X, but just because extreme SDO orbits hint at the presence of another body doesn't mean there has to be a Planet X 2.0.
"You can go back 100 years to claims of planets in the outer solar system and (their orbital anomalies) have all eventually gone away," said Hal Levison, a planetary scientist at the Southwest Research Institute in Boulder, Colo. "That should give you pause for thought. Just because there's not a good explanation for (the orbits of the scattered disc objects) besides another planet doesn't mean there won't be a good explanation in the future."
One leading alternative theory as to how SDOs got flung around is that during the sun's formative years, it grew up in a cluster of tightly packed stars - perhaps the gravitational instabilities caused by neighboring stars affected the objects in the outer solar system.
"Back at the time of the birth of the sun, the sun probably formed in a cluster of other stars. If true, they would have been close enough together to influence each other's outer planet systems, like where Sedna is," said Brown.
So for now, we'll just have to wait and see if more evidence presents itself - at the moment, evidence for Planet X 2.0 seems a little too thin.
Image credit: NASA, edit by Ian O'Neill