An undiscovered Mars-sized planet could be lurking in the outer solar system and influencing the tilt of distant Kuiper Belt Objects (KBOs), according to a new study published in the Astronomical Journal.
Proposed by Kat Volk, the study’s lead author, and Renu Malhotra, both at the University of Arizona’s Lunar and Planetary Sciences Laboratory (LPL), this object is not the hypothesized “Planet X” or super-Earth that some scientists have been searching for since January 2016.
According to Volk and Malhotra, a group of very distant Kuiper Belt Objects–mostly small, icy rocks–are tilted away from the orbital plane of the solar system, known as the invariable plane, by approximately eight degrees.
This tilt is believed to be caused by perturbation from an as-yet-undiscovered massive object.
“The most likely explanation for our results is that there is some unseen mass. According to our calculations, something as massive as Mars would be needed to cause the warp that we measured,” Volk said.
Volk and Malhotra studied the orbital plane tilts of more than 600 KBOs. All of these wobbles, or precess, while orbiting. Malhotra compares this wobbling to that exhibited by rapidly-spinning tops.
“Imagine you have lots and lots of fast-spinning tops, and you give each one a slight nudge. 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,” she stated.
“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.”
The Kuiper Belt starts near the orbit of Pluto, approximately 30 astronomical units or AU (with one AU equal to the average Earth-Sun distance or 93 million miles).
All the KBOs found to be tilted toward the solar system’s invariable plane are much more distant, located between 50 and 80 AU from the Sun.
To Volk and Malhotra, this is compelling evidence that they are being influenced by the gravitational pull of an object approximately 60 AU from the Sun, with a mass roughly that of Mars.
That object cannot be the hypothesized Planet X, which is believed to be somewhere between 500 and 700 AU from the Sun, too distant to perturb these KBOs.
The perturbing object cannot be a passing star because the tilt caused by that star would be temporary; after it passed by, the KBOs would return to their original plane.
Volk and Malhotra hope the new Large Synoptic Survey Telescope (LSST), scheduled for launch in 2020, will be able to find the perturbing object.