2023-10-11 04:00:14
The idea of a ninth planet within our solar system, put forward following certain observations, might ultimately be refuted in favor of a new understanding of gravity, inspired by galactic movements.
Harsh Mathur, professor of physics at Case Western Reserve University, and Katherine Brown, associate professor at Hamilton College, proposed this hypothesis following studying the effect of Milky Way on the objects of solar system external, assuming that the laws of gravity are dictated by a theory named Dynamic modified Newtonian (or MOND).
MOND suggests that Isaac Newton’s famous law of gravity is valid to a certain extent. Indeed, when the gravitational acceleration predicted by Newton’s law becomes sufficiently low, MOND predicts a different gravitational behavior.
A certain observational success of MOND on the galactic scale has led scientists to consider it as an alternative to “dark matter”, a type of matter hypothetical, gravitationally influencing celestial objects without emitting light.
“MOND is very good at explaining observations on the galactic scale,” Mathur said, “but I didn’t expect it to have noticeable effects on the outer Solar System.”
Their study, recently published in The Astronomical Journal, stems from interest in MOND following the 2016 announcement of orbital anomalies in the outer solar system, explained by the presence of a ninth planet.
Orbital anomalies have already led to major discoveries in the past. For example, the discovery of Neptune was due to its gravitational influence on nearby objects, and the precession of Mercury provided early support for the theory of relativity General Einstein.
Brown speculated that MOND’s predictions might contradict observations supporting the ninth planet hypothesis. “We wanted to see if the data supporting the ninth planet hypothesis would actually refute MOND,” she said.
On the contrary, Mathur and Brown found that MOND predicts precisely the clustering that astronomers have observed. They argue that, over millions of years, the orbits of certain objects in the outer Solar System would be aligned with the gravitational field of the galaxy.
Comparing the orbits of objects in the Ninth Planet dataset with the galaxy’s gravitational field, “the alignment was striking,” Mathur noted.
Although the current data set is limited, and other hypotheses may prove correct, this work highlights the possibility of the outer Solar System serving as a laboratory for testing gravity and studying fundamental problems in physics.
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