spaceSpace and Physics

New Study Questions Previous Evidence For Planet Nine


Jonathan O'Callaghan

Senior Staff Writer

Artist's impression of Planet Nine. Caltech/R. Hurt (IPAC)

Scientists have suggested that previous gravitational evidence thought to point towards the existence of Planet Nine may not be what it appears.

In a study led by the University of Colorado Boulder, the team suggested that “bumper car-like interactions” at the edge of the Solar System may explain the weird motions of some objects we can see out there. Their findings were presented at the 232nd meeting of the American Astronomical Society.


In 2016, Caltech astronomers Konstantin Batygin and Mike Brown proposed the existence of Planet Nine based on the clustering of Kuiper Belt Objects (KBOs) beyond Neptune. These objects suggest they are being shepherded by an unseen planet. So far, we haven’t found it.

A previous study in 2014 had suggested a similar conclusion to explain the orbit of the minor planet Sedna, which seems to be detached from the rest of the Solar System. Other bodies out at this distance also seem to be detached.

In this latest study, however, the researchers suggest that the unusual orbits of these objects may be the result of them bumping into each other and space debris, rather than a hidden planet. It may be that the collective gravity of these objects has clumped them together.

“You see a pileup of the orbits of smaller objects to one side of the Sun,” Jacob Fleisig, the lead author on the research, said in a statement. “These orbits crash into the bigger body, and what happens is those interactions will change its orbit from an oval shape to a more circular shape.”


The orbits of the objects were compared to the hour hand and the minute hands on the clock, with the former being larger objects like Sedna and the latter being smaller objects like asteroids. And as they collide together, they could all get tangled up with each other.

Don’t rule out Planet Nine just yet, though. Because Batygin told Popular Mechanics he did not agree with the theory, saying that there would need to be more mass in the Kuiper Belt for this explanation to work.

"Unfortunately, the self-gravity story suffers from the following complications," he said. "Both observational and theoretical estimates place the total mass of the Kuiper Belt at a value significantly smaller than that of the Earth. As a consequence, Kuiper Belt objects generally behave like test-particles enslaved by Neptune’s gravitational pull, rather than a self-interacting group of planetoids."

It’s probably not enough to rule against or in favor of Planet Nine just yet. But any bold scientific claim like this will, of course, need to stand up to the rigors of scrutiny, if it truly exists.


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