An artistic depiction of a Kuiper Belt Object (KBO), situated at the farthest edge of our solar system, an astounding 4 billion miles away from the sun. Credit: NASA, ESA, and G. Bacon (STScI)
The furthest regions of the solar system may contain either an additional planet or evidence that suggests amendments to the existing laws of gravity.
Two theoretical physicists have posited that the very observations prompting the search for a ninth planet may actually serve as intra-solar-system evidence for an adapted law of gravity, initially conceived to elucidate the rotational dynamics of galaxies.
Harsh Mathur, a physics professor at Case Western Reserve University, and Katherine Brown, an associate physics professor at Hamilton College, arrived at this conclusion after investigating the impact the Milky Way galaxy might have on celestial bodies in the outer solar system, assuming the gravitational laws were dictated by a theory known as Modified Newtonian Dynamics (or MOND).
Harsh Mathur. Credit: Case Western Reserve University
MOND suggests that Isaac Newton’s well-known law of gravity holds true only up to certain limits. Specifically, when the gravitational acceleration forecasted by Newton’s law falls below a certain threshold, MOND posits that a different type of gravitational behavior comes into play.
The efficacy of MOND in explaining phenomena on a galactic scale has led some scientists to view it as an alternative to the concept of “dark matter,” a theoretical form of matter that would exhibit gravitational influence without emitting light.
“MOND is highly effective in accounting for observations at the galactic level,” said Mathur, “though it was surprising to find that it could also have a significant impact on the outer reaches of the solar system.”
Their research has been recently published in The Astronomical Journal.
A Remarkable Synchronization
Previously, Mathur and Brown had explored the implications of MOND on the dynamics of galaxies. However, their interest was piqued in the theory’s local effects when astronomers reported in 2016 that certain objects in the distant solar system exhibited orbital irregularities potentially explained by a ninth planet.
Historically, orbital anomalies have paved the way for significant discoveries. For example, Neptune was found due to its gravitational effects on nearby celestial bodies, Mercury’s slight orbital precession supported Einstein’s theory of general relativity, and contemporary astronomers have inferred the existence of a supermassive black hole in the center of our galaxy based on orbital mechanics.
Brown noted that MOND’s projections could conflict with the observations that sparked the quest for a ninth planet. “We were curious to see if the data supporting the Planet Nine theory would simultaneously invalidate MOND,” she remarked.
Katherine Brown. Credit: Hamilton College
Upon further investigation, Mathur and Brown discovered that MOND accurately predicts the observed clustering of certain celestial bodies in the outer solar system. Over millions of years, they contend, the orbits of these objects could align with the gravitational field of the galaxy itself.
When the researchers matched the orbits of these objects from the Planet Nine dataset with the gravitational field of the galaxy, Mathur noted, “the correspondence was remarkable.”
While acknowledging the limitations of the existing dataset, the authors caution that various other interpretations could still prove accurate; some astronomers have suggested, for instance, that these orbital irregularities are due to observational biases.
“Regardless of the final conclusion,” said Brown, “this investigation underscores the potential of the outer solar system as a testing ground for probing the laws of gravity and addressing foundational questions in physics.”
Reference: “Modified Newtonian Dynamics as an Alternative to the Planet Nine Hypothesis” by Katherine Brown and Harsh Mathur, 22 September 2023, The Astronomical Journal.
DOI: 10.3847/1538-3881/acef1e
Table of Contents
Frequently Asked Questions (FAQs) about Modified Newtonian Dynamics (MOND)
What is the main argument presented by the two theoretical physicists?
The main argument presented by Harsh Mathur and Katherine Brown is that the observational anomalies in the outer solar system, which have led to the hypothesis of a ninth planet, might actually be evidence for a modified law of gravity. This law, known as Modified Newtonian Dynamics (MOND), was initially developed to understand the rotation of galaxies.
What is Modified Newtonian Dynamics (MOND)?
Modified Newtonian Dynamics (MOND) is a theory suggesting that Newton’s law of gravity holds true only up to a certain point. When the gravitational acceleration predicted by Newton falls below a certain threshold, MOND posits that a different kind of gravitational behavior takes over.
How does MOND challenge the concept of “dark matter”?
MOND has been successful in explaining phenomena on galactic scales, which led some scientists to consider it as an alternative to “dark matter.” Dark matter is a hypothetical form of matter that would have gravitational effects but would not emit any form of light.
Why did the physicists decide to investigate MOND’s effect on the solar system?
The physicists were intrigued by MOND’s potential local effects when astronomers reported in 2016 that some objects in the outer solar system exhibited orbital anomalies. These anomalies were initially thought to be explainable by the existence of a ninth planet.
What were the findings when MOND was applied to the outer solar system?
Upon applying MOND to the data from the outer solar system, Mathur and Brown found that MOND precisely predicts the clustering of certain celestial bodies. Over millions of years, the orbits of these objects would align with the gravitational field of the Milky Way galaxy.
What are the implications of these findings?
The findings imply that the outer regions of our solar system could serve as a new testing ground for laws of gravity and may offer an alternative explanation for phenomena that were previously attributed to dark matter or additional planets.
Are the findings definitive?
The authors caution that the current dataset is small and other interpretations might still prove to be correct. For example, some astronomers have suggested that the observed orbital anomalies may be the result of observational bias.
What is the significance of this research?
Regardless of the final outcomes, this research underscores the potential of the outer solar system to serve as a laboratory for probing the laws of gravity and addressing foundational questions in physics.
More about Modified Newtonian Dynamics (MOND)
- Modified Newtonian Dynamics as an Alternative to the Planet Nine Hypothesis: Published Research
- What is Modified Newtonian Dynamics (MOND)?
- Dark Matter: An Overview
- Case Western Reserve University: Harsh Mathur’s Faculty Profile
- Hamilton College: Katherine Brown’s Faculty Profile
- The Astronomical Journal
- Planet Nine Hypothesis: A Brief Overview
- The Kuiper Belt and Beyond
6 comments
Ok, this is game-changing. I’d love to see what traditional physicists have to say about it. But if it holds up, textbooks will need a serious update, no joke.
it’s insane how we might not even need to find a ninth planet now. But what does this mean for the hunt for dark matter? Are we back to square one?
If the dataset is small, should we even be considering this as credible? I mean, it’s an interesting theory but let’s not jump the gun.
Hold on, MOND has been around for a while, right? Why are we just now seeing its potential impact on our solar system? Seems a bit late in the game.
I’ve always been skeptical bout these “alternative” theories, but the evidence seems to be piling up. MOND or not, we’re definitely on the cusp of something big here.
Wow, this is mind-blowing stuff! If MOND turns out to be true, it would change so many things in physics and beyond. Can’t wait to see where this research goes.