The outer edge of our solar system is hiding a massive object the size of Mars that could be the tenth planet found to orbit the sun.
The as-yet unconfirmed world, known as ‘Planet 10’, has been proposed after scientists spotted that icy objects in a region beyond Neptune have wonky orbits.
The reason for their crooked trajectories is unknown, and researchers think that a large, possibly planetary, mass is causing the strange shifts.
The mysterious mass, University of Arizona researchers show, has given away its presence only by controlling the orbital planes of a population of space rocks known as Kuiper belt objects (KBOs) in the icy outskirts of the solar system.
Earth and similar planets orbit the sun in roughly the same plane, but smaller KBOs are far enough from the gravitational influence of bigger planets that they can orbit the sun at angles to this plane at ‘orbital tilts’.
KBOs are debris leftover from the formation of the solar system, and most of them orbit with orbital tilts, also known as inclinations, at what scientists call the ‘invariable plane’.
However, the researchers calculated that KBOs at the outer edges of the Kuiper belt orbit at a tilt eight degrees out from the invariable plane.
This, they suggest, means that the gravitational pull of a large mass – possibly a new planet – is pulling on them.
‘The most likely explanation for our results is that there is some unseen mass,’ said Dr Kathryn Volk, a postdoctoral fellow at Arizona’s Lunar and Planetary Laboratory and the lead author of the study.
‘According to our calculations, something as massive as Mars would be needed to cause the warp that we measured.’
The Kuiper belt is an icy, halo-like region that extends outwards from Neptune to a distance around 55 times further from the sun than Earth is, or 55 AU.
It is thought to be the remains of the violent and chaotic collisions that led to the formation of the planets.
There are an estimated 33,000 objects more than 60 metres across in the belt and three dwarf planets.
In their study, the researchers examined the tilt angles of the orbital planes of more than 600 objects in the Kuiper belt.
They found that KBOs beyond 50 AU from Neptune had their inclination warped, which calculations suggest must be caused by an object around the size of Mars.
‘It’s not what we expect if the only planets in our solar system are those we know of,’ Dr Volk told New Scientist.
The object, which could be the tenth planet in our solar system, may have arrived in the outer belt region after a collision with another planet.
‘If it’s the size of Mars, that is a pretty big object, which would suggest it would be most likely scattered out there by planetary movements further in,’ Dr Volk said.
The new object would be different from, and much closer to Earth than, the so-called Planet Nine discovered next year, a planet whose existence remains unconfirmed.
A study published this week cast doubt on the existence of Planet Nine after scientists first spotted the large object in the Kuiper belt last year.
Since the planet was first proposed, several studies have attempted to find evidence of its existence far beyond Neptune based on several signatures it would leave.
Now, new results from a four-year survey have identified eight large-orbit trans-Neptunian Objects (TNOs), which could help to pinpoint a planet in the vicinity based on a phenomenon known as ‘clustering.’
But, the survey found no evidence of clustering whatsoever, and scientists now say ‘detection biases’ could be to blame for earlier data that favour Planet 9.
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