According to experts, our Sun is tilted by about 6 degrees compared to the sun’s equator. The reason behind this has remained an astronomical mystery for decades. Now, experts believe they’ve finally found an answer: Planet Nine. Elizabeth Bailey is an astrophysicist and planetary scientist at the California Institute of Technology in Pasadena.

According to her, not only did planet nine tilt our sun by six degrees, the missing “planet may have tilted the other planets over the lifetime of the solar system.” Planet Nine is the still undiscovered celestial body believed to exist in the outermost edges of our solar system and was predicted by the work of Konstantin Batygin and Mike Brown in January 2016.

According to experts, all of the planets located in our solar system orbit in a flat plane with respect to our sun, within a few degrees of each other. However, experts not that that plane rotates at a six-degree tilt compared to the sun, which gives us an appearance that our sun isn’t the way it should be.

For years no one was able to explain how something like this was possible.

What could cause our sun –the most massive body in our solar system— to tilt by six degrees? In fact, the sun is oriented differently than everything else in our solar system.

“It’s such a deep-rooted mystery and so difficult to explain that people just don’t talk about it,” says Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy.

To get to the bottom of the mystery, Bailey and fellow researchers ran computer simulations and found out that the tilt of the eight planets could be explained by the gravitational influence of Planet nine. In an interview with Space.com, Bailey noted that while this is one theory, there are still other potential explanations for the curious tilt our solar system has adapted over the 4.5-billion-years-ish lifetime of the solar system.

One such explanation is that there may have been an imbalance in the mass of the nascent sun’s core. According to Konstantin Batygin and Mike Brown, our sun is most likely orbited by a –unseen- massive planet, about ten times the size of Earth, with a staggering orbit that is believed to be around 20 times farther from the sun than that of 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,” says Batygin.

The curious tilt of our sun and remaining bodies in the solar system has long been a mystery for astronomers. Experts believe that planet’s nine angular momentum – In physics, angular momentum (rarely, moment of momentum or rotational momentum) is the rotational analog of linear momentum— is the creating a massive impact on the solar system based on its location and size.

While this is one of the explanations to the curious tilt of our solar system, experts still have to find the rogue planet.