There could be a planet hidden in the far reaches of our solar system. And astronomers have published new details about what it probably is, if it really exists.
Planet 9, according to a new article published online Feb. 10 in Physics Reports, is probably five to ten times the mass of Earth. And probably travels along an elongated orbit that peaks at 400 times the distance from Earth to the sun. This orbit is also likely 15 to 25 degrees outside the main orbital plain of our solar system, where most planets orbit.
The existence of Planet Nine, as the sister site of Live Science, Space.com, reported earlier, is an idea that has become popular with astronomers since it was seriously proposed in 2014. Researchers suspect the existence of the planet because of the objects in the Kuiper Belt, a ring of debris in the outer solar system. These objects tend to cluster in ways that suggest that the gravity of something big is pulling on them.
And the evidence only grew stronger. In a separate article, published Jan. 22 in The Astronomical Journal, some of the same authors of the Physics Report article have estimated the likelihood that Planet Nine will not exist at just 1 in 500. [Amazing Astronomy: Victorian-Era Illustrations of the Heavens]
Strongly suspecting that the dark planet exists is not the same thing as knowing it is real, however. The good news is that this new research suggests that Planet Nine is significantly closer than previously thought. But astronomers still have plenty of room to look for it.
The authors of the Physics Reports article have, however, raised the possibility that there is no planet out there. They added that, however strong the current evidence, this chance must be "taken seriously."
The most likely alternative explanation is that the humanity image of the Kuiper belt is incomplete and that objects only appear to cluster because of some bias in efforts to detect them. It is also possible, the authors have suggested, that clustering results from the "self-gravity" of the Kuiper Belt, acting on its own objects and not arising from a tug from some hidden planet.
Still, astronomers have become more convinced by the evidence of Planet Nine in recent years. And now they are making significant progress to locate it in space.
Originally published in Living Science.