According to some scientists, there may be a ninth planet in our solar system, in addition to the eight known planets. While this hypothesis does not include Pluto, it is based on the assumption of a massive unknown planet located in the far reaches of the solar system. However, a recent study presents an alternative explanation, suggesting that the characteristics of the outer solar system could be linked to modified gravity theories, potentially replacing the need for dark matter.
Astronomers first noticed discrepancies in the orbit of Uranus in the 19th century, which led them to propose the existence of an unknown object exerting gravitational influence. This eventually led to the discovery of Neptune. In 2016, astronomers once again suggested the presence of an unknown planet based on peculiar orbital patterns of objects within the Kuiper belt.
However, a team of scientists now presents a radical solution by modifying the theory of gravity itself. Even though Newton’s universal law of gravity has effectively explained the structure of the universe, it still has its limitations. Dark matter was proposed as an explanation for these limitations, but despite extensive research, it has never been found. One alternative theory is Newton’s modified dynamics (MOND), which has been supported by observations in star clusters and over 150 galaxies.
Based on the results of a new study, if MOND is indeed accurate, the orbits of some objects in the outer solar system should gradually align with the gravitational field of the Milky Way over time. Researchers were astonished to find that this alignment does indeed occur.
“This is a remarkable consistency,” says Harsh Mathur, co-author of the study. “MOND explains observations at the galactic level quite well, but I did not expect it to have a noticeable effect on the outer solar system.”
Nevertheless, despite these intriguing findings, the authors acknowledge that the data sample is still small and other plausible explanations exist. The search for dark matter and the potential ninth planet will likely continue.
Katherine Brown, another co-author of the study, emphasizes that “this work demonstrates the outer solar system’s potential as a laboratory for gravity testing and the exploration of fundamental physics.”
The study has been published in the astronomical journal and can be found here.