Somewhere beyond Pluto might be a ninth planet. But now astronomers are not sure

Planet Nine, a hypothetical ninth planet in the outer region of the Solar System, has almost become impossible to trace by scientists and astronomers. Planet Nine is said to be somewhere beyond the orbit of Pluto and lies in a very dark and cold place in the Solar System, which makes it hard to detect.

In the past, scientists have given several reasons for this. One would be that no one has actually seen it yet and it’s only on the paper. Another is the real possibility that it is just not there. Or it might not be a single planet at all, but a swarm of rocks instead. But according to a recent research; it is more than all of that.

Mystery of Planet Nine

New research conducted by physicists Katherine Brown of Hamilton College and Harsh Mathur of Case Western Reserve University deduced that there is something missing from our current model of gravity as described under the general relativity theory.

According to their recent study, the subtle abnormalities in the orbits of various objects some attribute to a hidden planet are also consistent with a different kind of gravitational model – one called Modified Newtonian Dynamics (MOND).

The flaws in Newton's law of universal gravitation were resolved by Einstein's theory of general relativity. MOND is an alternative solution that proposes other gravitational effects take over when Newtonian gravitational acceleration drops below a certain threshold.

Because MOND can describe the gravitational behaviour of galaxies that don't seem to be tied to normal matter – unexpected rotation curves and lensing effects – it's an attractive alternative to dark matter. But it hasn't really been studied on smaller scales.

"MOND is really good at explaining galactic-scale observations," Mathur says. "I hadn't expected that it would have noticeable effects on the outer Solar System."

Brown and Mathur thought that these clustering observations might not be compatible with MOND. They undertook an investigation, modelling the orbits of outer Solar System Kuiper Belt objects under MOND to observe how they behave.

Surprisingly, what they ended up with was a bunch of rocks behaving pretty much exactly like the observed clustering. Their calculations suggest under MOND theory, some of the objects in the outer Solar System should be dragged into alignment with the gravitational field of the Milky Way galaxy over time.

It's not enough to confidently assert that MOND is responsible for the strange behaviour of these distant rocks, rather than a planet.

"Regardless of the outcome," Brown says, "this work highlights the potential for the outer solar system to serve as a laboratory for testing gravity and studying fundamental problems of physics."

(With inputs from agencies)

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