It’s a world, it’s a math error, it’s … new physics?

by | October 25, 2023, 2:21 PM | Solar Systems

orbits of KBOs
Credit Katherine Brown & Harsh Mathur

When I was little, I was totally into all those “In Search of…” shows. There are so many cool mysteries in history waiting to be solved, and I love that I’ve gotten to see some of these great mysteries get solved. The giant squid… it’s real. Black holes… they totally exist… The ancient pyramids – totally full of hidden rooms. Scientists sometimes get to find some pretty awesome stuff.

And as an adult, I find there are both old mysteries and new ones waiting to be solved. Was there life on Mars? Is there life in Europa? Does our Solar System have any additional large planets? As I approach my 50th Birthday, I find myself wondering just what will be solved in my lifetime.

The big planet… I think that is the most likely to be proven or disproven in the near future.

In 2016, astronomers Michael Brown and Constantin Batygin proposed the existence of a large world in the outer solar system that has been gravitationally influencing the orbits of small worlds like Sedna that orbit in the outer solar system. The maths seemed to make sense. The data visualizations showing how the gravity of some additional large object could affect what we’re seeing definitely made sense, but…

Many years of searching all the existing databases of images, and observing campaigns using NEOWISE and the 8-meter Subaru telescope have all failed to find this theorized world, and folks now have to wonder, could what we see have another cause? Even Brown has been willing to admit, if Planet 9 isn’t found by the upcoming Vera Ruben Observatory’s Survey, they’ll need another explanation for what they’re seeing.

There have already been several papers trying to show how Brown and Batygin’s interpretation of current observations may be wrong, and a 9th planet may not be needed.

And now… there is also a paper saying the lack of an observable planet may be evidence that our understanding of gravity may need work.

And to be fair, we know our current theory of gravity works really well for some distances and some masses and velocities. Inside black holes, things break down.

And… At very large distances… we don’t actually know if gravity totally works. This is because of dark matter. Invisible to our standard light-detecting sensors, there is stuff out there capable of bending light with its gravity while also – to unknown degrees – altering the orbits of stars in galaxies, and galaxies in galaxy clusters… and of the evolution of our universe as a whole.

The reason I say, “to unknown degrees” is because a small change in how gravity works at the largest scales can also explain a lot of what we see.

The idea that Modified Newtonian Gravity can explain how things orbit one another at massive scales was mathematically developed by Mordehai Milgrom in 1983 and has been plugged away at, ever since.

And now, in a new paper in the Astronomical Journal written by Katherine Brown and Harsh Mathur, researchers test if Modified Newtonian Gravity, also called MOND, can explain what we can see as well as a 9th planet we haven’t seen.

Reference: Katherine Brown and Harsh Mathur 2023 AJ 166 168 10.3847/1538-3881/acef1e