Astronomers may have found a 10th planet the size of Mars

Astronomers have not yet officially confirmed the existence of Planet Nine, a hypothetical world believed to orbit the sun from the outer reaches of the solar system, and it may have already been replaced as the most distant planetary mass object in our system, according to a new study.

Back in 2016, a team of scientists from Caltech discovered several distant objects with extremely unusual orbits that could be explained by the existence of a planetary mass object about 10 times the size of Earth. That hypothetical world,  Newsweek explained, was named Planet Nine.

Now, writing in the Astrophysical Journal, University of Arizona researchers Kat Volt and Renu Malhotra presented evidence of yet another, previously unknown planetary mass object that they believe has been influencing the orbital patters of icy objects located in the Kuiper Belt. The new planet, they said, would actually be much closer and much smaller than its predecessor.

Volk and Malhotra analyzed the orbits and inclinations (tilt angles) of more than 600 Kuiper Belt Objects (KBOs) and discovered that the most distant of these space racks are actually tilted away from the orbital plane that they should be resting on by around eight degrees. What that means is that something is influencing them, causing the orbital plane of the outer solar system to warp.

“The most likely explanation for our results is that there is some unseen mass,” Volk, the lead author of the new paper as well as a postdoctoral fellow at the university’s Lunar and Planetary Laboratory (LPL), said in a statement. “According to our calculations, something as massive as Mars would be needed to cause the warp that we measured.”

Unconfirmed object would be roughly the same size as Mars

Specifically, Volk and Malhotra found that the average plane for KBOs located more than 50 astronomical units (AU) from the sun warps away from the one upon which they should exist, Newsweek explained. Based on their calculations, they determined that a planet about the same mass as Mars and located about 60 AU from the sun could be responsible.

“Imagine you have lots and lots of fast-spinning tops, and you give each one a slight nudge,” said Malhotra, a professor of planetary sciences at LPL. “If you then take a snapshot of them, you will find that their spin axes will be at different orientations, but on average, they will be pointing to the local gravitational field of Earth.”

“We expect each of the KBOs’ orbital tilt angle to be at a different orientation, but on average, they will be pointing perpendicular to the plane determined by the sun and the big planets,” she added. Past the 50 AU point, the study authors explained, the orbital plane should be relatively flat – but it isn’t, and between 50 and 80 AU, it actually bends away from the expected plane.

The researchers said that there is no more than a 2% chance that this phenomenon is a statistical fluke, indicating that there is likely something out there actually causing this effect. Based on the duo’s calculation, they determined that a Mars-mass planetary object located approximately 60 AU from the sun, with an orbital tilt of eight degrees, would have enough gravitational influence to warp the orbital plane of distant KBOs by around 10 AU to either side.

“The observed distant KBOs are concentrated in a ring about 30 AU wide and would feel the gravity of such a planetary mass object over time, so hypothesizing one planetary mass to cause the observed warp is not unreasonable across that distance,” Volk said, adding that the influence could not have been caused by Planet Nine, as it is too big and much too far away.


Image credit: Heather Roper/LPL