The mysterious Planet Nine could be responsible for the slight tilt of our solar system relative to the sun, new research suggests.
Writing in the Astrophysical Journal, researchers from the California Institute of Technology say the hypothetical massive planet at the edge of the solar system could be the reason the planets orbit at a six-degree slant relative to the sun.
"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," says Elizabeth Bailey, a graduate student at Caltech and lead author of a study about the tilt.
Until now, astronomers had been unable to explain why all the planets are on more or less on the same plane and why that plane is tilted six degrees.
"It's such a deep-rooted mystery and so difficult to explain that people just don't talk about it," said Brown.
Planet Nine, which has yet to be seen, could be 10 times the size of Earth and orbit 20 times further away than Neptune. The mysterious planet appears to orbit on a plane that is 30 degrees off the rest of the planets, researchers said.
It is believed the planet is responsible for the large grouping of objects in the Kuiper Belt, which lies beyond Neptune.
"It continues to amaze us; every time we look carefully we continue to find that Planet Nine explains something about the solar system that had long been a mystery," said Konstantin Batygin, an assistant professor of planetary science.
Planet Nine’s odd orbit relative to the rest of the planets likely causes a “multi-billion” year wobble on the solar system, with Brown adding that calculations about the effect of the planet show that a six-degree tilt “fits perfectly.”
Next up for astronomers is to try to figure out why Planet Nine has such an unusual orbit.
One theory posits that the “planet may have been ejected from the neighborhood of the gas giants by Jupiter, or perhaps may have been influenced by the gravitational pull of other stellar bodies in the solar system's extreme past.”