Planet Nine may be causing the entire solar system to tilt

The existence of Planet Nine, the massive unconfirmed world located at the outer edge of the solar system, may be causing the sun to become tilted slightly, forcing its entire planetary system to “wobble” out of alignment, according to a soon-to-be-published new study.

While all of the currently confirmed planets in the solar system orbit the Sun in a flat plane within a few degrees of each other around the sun, the plane rotates at a six-degree tilt with respect to the sun, Caltech planetary astronomy professor Mike Brown explained Wednesday in a statement.

This phenomenon makes it appear as though the sun itself is tilted at an unusual angle, he noted, something which scientists have thus far not been able to explain. However, if there is a massive planet about 10 times the size of Earth with an orbit an average of 20 times farther from the sun than Neptune located in the outer reaches of the solar system, it could well be responsible.

Brown and his colleague Elizabeth Bailey, a graduate student at Caltech and lead author of the new study, believe that such a massive world could drastically alter the solar system’s physics by traveling at an orbit approximately 30 degrees off the orbital plane of the other planets. By doing so, it could also influence the orbit of a large number of Kuiper Belt objects as well.

Size, distance from the sun could make Planet Nine a disruptive influence

“Because Planet Nine is so massive and has an orbit tilted compared to the other planets, the solar system has no choice but to slowly twist out of alignment,” said Bailey, whose research was presented Tuesday as part of the American Astronomical Society’s Division for Planetary Sciences annual meeting in Pasadena and will appear in the Astrophysical Journal.

In fact, the proposed world’s purported influence on the Kuiper Belt is how Brown and fellow Caltech researcher Konstantin Batygin originally stumbled upon its existence, the study authors explained. The angular momentum (mass multiplied by its distance from the sun) of this planet could be having a disruptive influence on the normally smooth-spinning solar system.

“Planet Nine is the first thing that has been proposed to tilt the solar system that doesn’t depend on early conditions,” Bailey told, “so if we find Planet Nine, we will be able to see if it’s the only thing responsible for the tilt, or if anything else may have played a role.”

Since the other planets exist along a flat plane, the researchers noted, their angular momentum keeps the solar system in balance. The unusual orbit of the quite large Planet Nine, however, would add a several billion year wobble to the system, and based on its hypothesized size and distance from the sun, a six-degree title would be a perfect fit. The question that remains to be answered is: how would Planet Nine have acquired such an unusual orbit in the first place?

While additional research is needed to definitively solve that mystery, Batygin hypothesizes that Jupiter may have ejected it from the region of the solar system occupied by the gas giants, or that it could have been influenced by the gravitational pull of other objects in the distant past. For the time being, the Caltech researchers continue to comb the skies in search of evidence that the new planet is traveling along its projected path – a search that could take several years.


Image credit: Caltech/R. Hurt (IPAC)