Our Sun’s Quirky Tilt Means Planet Nine Might Actually Exist

By George Dvorsky on at

New research links the odd and unexplained six-degree tilt of our Sun to an undiscovered planet in the outer reaches of our solar system. It’s even more evidence that planet Nine is for real.

A new paper published in the Astrophysical Journal posits the hypothesis that a large and distant planet at the outer reaches of the solar system is causing the unusual tilt of our sun.

All planets in our solar system orbit in a flat plane with respect to the sun (give or take a few degrees), but that plane is tilted six-degrees with respect to the sun. The reason for this crooked angle hasn’t been explained. However, as Caltech’s Konstantin Batygin, Mike Brown, and graduate student Elizabeth Bailey show in their new study, a large planet far, far away could produce this very effect.

Earlier this year, Batygin and Brown rocked the science world when they presented evidence pointing to the existence of an undiscovered planet—one about 10 times the size of Earth and with an orbital period of around 15,000 years. The smoking gun was the unlikely orbital configuration of celestial objects in orbit beyond the Kuiper Belt—configurations that could only be explained through the presence of a large gravitational body in the outer reaches of the solar system.

In their latest study, the researchers claim that Planet Nine’s gravitational effects are also being felt at the very core of the solar system. “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,” noted Bailey in a statement.

The solar system’s tilt has troubled astronomers for years, and they’ve been unable to come up with satisfactory explanations. Normally, because other planets in the solar system reside along a flat plane, their angular momentum helps to keep the whole disk spinning smoothly.

Our Sun’s Quirky Tilt Means Planet Nine Might Actually Exist
Planet Nine—if it exists—is in an orbit that’s about 30 degrees off from the other planets’ orbital plane. Over the course of 4.5 billion years, this has produced the quirky six-degree angle in the sun’s tilt. (Image: E. Bailey et al., 2016)

But Planet Nine, and its unusual—albeit hypothetical—orbit, is adding a wobble to our solar system—one 4.5 billion years in the making. Previous calculations suggest that Planet Nine’s orbit is about 30 degrees off kilter from the other planets’ orbital plane. Intriguingly, given the hypothesised size, distance, and orbital angle of planet Nine, a six-degree stellar tilt fits perfectly.

“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 Batygin.

Looking ahead, astronomers would like to figure out how Planet Nine achieved its strange and distant orbit. One theory is that Jupiter kicked it out as the gas giant migrated inwards in the early days of the solar system. Astronomers also need direct evidence of the camera shy Planet Nine in the form of an actual sighting. Encouragingly, Brown and Batygin are working with astronomers to do exactly that. [Astrophysical Journal]