Mars-sized planet may be hiding at the edge of our solar system

UNITED STATES: A mysterious celestial body may be lurking in the frozen, far-flung reaches of the solar system, scientists say.

This is not the proposed ‘‘Planet Nine,’’ a ginormous body that Caltech scientists believe could be tugging at the orbits of the solar system’s most distant inhabitants. And it’s not Pluto.

Instead, University of Arizona astronomers Kat Volk and Renu Malhotra say it’s a Mars-sized body in the Kuiper belt, a swarm of small icy objects that extends beyond the orbit of Pluto. If the Arizona and Caltech researchers are right, then these proposed bodies could bring the number of planets in our solar system to 10.

Volk and Malhotra haven’t seen their new planet, but they say they can sense its presence. They describe an odd distortion in the orbits of objects in the outer part of the Kuiper belt, ones that are between 50 and 80 AU away (AU stands for astronomical unit, or the distance from the sun to Earth, about 150 million kilometres).

Though most of the nearer bodies in the solar system circle the sun in the same plane, largely thanks to Jupiter’s steadying heft, these far away Kuiper belt objects (KBOs) orbit at all kinds of wonky angles.

That in itself wouldn’t raise too many questions. But when Volk and Malhotra analysed these orbits in search of the average plane, they found it was offset by about 8 degrees.

‘‘It’s significant,’’ Volk said. ‘‘And the most likely explanation is this object on the outer solar system.’’

If there is a planet out there with roughly the same mass as Mars, its gravity could pull on the orbits of small KBOs, dragging them out of the ‘‘invariable plane’’ that Earth, Jupiter and the rest of the planets inhabit.

The Caltech researchers used similar logic to infer the presence of Planet Nine, arguing that this ‘‘massive perturber’’ is responsible for peculiarities in the point at which KBOs are closest to the sun.

‘‘It’s the same idea of indirectly detecting a planet by its effects,’’ Volk said.

For their study, Volk and Malhotra examined the orbits of about 600 KBOs. Scientists know of roughly 2000 KBOs, but they believe there may be as many 100,000 of significant size.

‘‘It would be useful to have more Kuiper belt objects to make sure this is a real signal,’’ Volk acknowledged. But even so, their analysis suggests there’s only a 1 to 2 percent chance that the results are a result of a fluke in the data.

Alessandro Morbidelli at the Cote d’Azur Observatory, France, said he found it hard to believe that astronomers could have missed something as big as a planet so nearby. (The Caltech scientists’ ‘‘Planet Nine’’ is said to be 10 times as distant, which explains why it’s been so hard to track down.)

‘‘I am dubious that a planet so close and so bright would have remained unnoticed,’’ Morbidelli said.

Said Volk: ‘‘We have a good sense of the outer solar system, but it would not surprise me at all if there are very distant things we have missed.’’ – Washington Post