Our solar system officially contains eight planets, but some scientists say there may be a ninth. And this doesn’t just apply to Pluto fans; data shows that a huge unexplored world is hiding in the dark slums. Now a new study has shown that the solar system’s external oddities can be explained by modified theories of gravity that are alternatives to the idea of ​​dark matter.

Astronomers measuring the orbit of Uranus in the 19th century noticed some discrepancies between observations and predictions and concluded that Uranus was affected by the gravitational pull of a large, invisible body. Of course, as a result, the planet Neptune was discovered in a short time.

In 2016, astronomers made a similar prediction: Based on the strange orbital patterns of six icy objects in the Kuiper belt, an unknown planet with about 10 Earth masses could be poking them out of the shadows. More evidence from other objects and even the Sun’s tilt seemed to support this idea.

But other scientists have proposed alternative explanations, such as gravitational interactions between planets, a distant disk of rock and ice, or even a mini black hole. And now the team has proposed an even stranger idea to change the theory of gravity.

This is not as outrageous a statement as it seems. Although Newton’s law of universal gravitation explains the large-scale structure and motion of the universe quite well, it fails in some cases. For most of the century, dark matter has been the favorite plug to fill the gaps left by Newton’s law in our cosmological models. This mysterious substance is believed to permeate the universe without reflecting or emitting any light, and interacts with ordinary matter only through strong gravity.

As is widely accepted, dark matter has never been directly detected despite numerous experiments conducted to search for it. Some scientists suggest we may need to adjust Newton’s law of gravity instead. For example, the effect of gravity may be stronger at low accelerations than Newton described, eliminating the need for dark matter. This model is known as modified Newtonian dynamics (MOND), and evidence of it has recently been found in star clusters and more than 150 galaxies.

In a new study, theoretical physicists applied MOND to a dataset used in the search for the ninth planet. According to their model, if MOND works, the orbits of some objects in the outer solar system should align with the gravitational field of the Milky Way galaxy over millions of years. And to the team’s surprise, they found that the clustering of orbits of these objects matched exactly the observations in our solar system.

“This agreement was remarkable,” said Harsh Mathur, one of the authors of the study. “MOND does a really good job of explaining galactic-scale observations, but I didn’t expect it to have a noticeable impact on the outer solar system.”

As intriguing as the study is, the team acknowledges that the data set is quite small and there are many other possible explanations. In the meantime, the search for both dark matter and the ninth planet is likely to continue.

“Whatever the outcome, this work highlights the potential of the outer solar system as a laboratory for testing gravity and studying fundamental problems in physics,” said study co-author Kathryn Brown. Source