Gravity Acting Up?

Scientists theorise knowledge on this force is far from complete.

In a country where science is a mandatory subject, it is difficult to forget the experiments, laws and equations that have been drilled into our heads since year 7. It is because of this that we have always felt comfortable in our knowledge of the world around us. However, what if something happened that changed the way we understood science? What if something we thought was common knowledge has changed? Well, something has happened, and what has changed is the theory of gravity.

Planet Nine: Our Solar System’s Mystery Member

Back in 2016, a group of researchers discovered an anomaly occurring in the Kuiper Belt positioned just beyond Neptune. The Kuiper Belt is essentially a huge asteroid belt that encircles our solar system consisting mainly of small bodies and remnants from when the solar system first formed. It is home to most of the known dwarf planets, Pluto being the most notable example, and many of the moons in our solar system may have originated there.     

The anomaly that had been found showed that some of the objects in orbit were being pulled into an abnormal cluster, something that should not have been possible. The objects would have to be heading towards something at least 10 times the size of the earth. This led scientists to theorise the existence of a new and undiscovered ninth planet in our solar system with a mass large enough to cause this anomaly. However, even after years of searching for this planet, dubbed ‘planet nine’, no more substantial evidence has been found to back up its existence.

Attempting to find another explanation for the anomaly, a new study was published on the 22nd of September this year. This study proposed that, instead of these gravitational anomalies being caused by a planet orbiting our sun, there are no anomalies at all. Its suggests that all inconsistencies are irradicated when applying an alternative concept of gravity called the Modified Newtonian Dynamic (MOND).

 MOND: Re-Learning Gravity

As we all learnt in school, Newton’s laws state that the harder you push an object, the faster it moves. MOND, however, makes a few edits to this theory. It suggests that objects which are moving slowly do not need as much force to speed up as we originally thought. This leads to the conclusion that stars on the outskirts of spiral galaxies are experiencing a greater gravitational pull than newton’s laws suggest. In essence, the objects in the Kuiper Belt are being pulled by the entire Milky Way.

MOND is not actually a new theory. It was conceived in 1983 as an alternative theory to dark matter (invisible particles that make up 27% of all matter). Dark matter was a proposal to explain why the gravitational pull of galaxies does not match up with the masses of the stars and planets inside them. MOND, whilst not completely compensating for all the missing mass, did explain how said galaxies are able to hold themselves together. The original goal of the team had been to rule out MOND as an explanation for planet nine, however they were surprised to find that when applied it completely solved the problem. Author of the study Harsh Mathur, stated that “MOND is really good at explaining galactic-scale observations, but I wouldn’t have expected that it would have noticeable effects on the outer solar system”.

It's All Theoretical

Of course, many people are not convinced by the planet nine/MOND theory, and many other explanations have been proposed. For example, some scientists have suggested that a tiny black hole could be responsible for pulling on surrounding objects. Everything is at most a theory, nothing has been proved nor disproved as there is no way of understanding with our level of technology. Micheal Brown who co-proposed the planet nine hypothesis said himself that: “the chances [of this being true] are low. It’s probably just a normal planet”. However, if MOND is the solution to the mystery of planet nine or not, the researchers believe the theory will play an important part in understanding our universe.