Planet Nine: hidden world at the edge of the solar system could be something else

The elusive "planet nine" hidden in our solar system may be something else entirely, scientists say.

Objects at the far reaches of the solar system behave as if they are being pulled around by an object that we cannot see - and scientists suggest that this may be the result of a large planet we cannot see.

In a paper published in The Astronomical Journal, labelled Modified Newtonian Dynamics as an Alternative to the Planet Nine Hypothesis, researchers Harsh Mathur, a professor of physics at Case Western Reserve University, and Katherine Brown, an associate professor of physics at Hamilton College, proposed the mysterious movements of objects at the edge of our solar system are not the result of a planet but are instead the result of a modified law of gravity.

The researchers plotted what would happen if the objects were governed Modified Newtonian Dynamics or MOND. This suggests that Newton’s usual gravity only works up to a point and that in the outer regions of galaxies, for instance, gravity behaves in unusual ways.

They found the data lined up, and applying the MOND theory to the existing observations seemed to predict them exactly. “The alignment was striking,” said Professor Mathur.

However, they state that the findings do not rule out planet nine.

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