New York, Jun 25 (IANS): Researchers, including one of Indian-origin, have found evidence of an unknown, Mars-sized "planetary mass object" lurking in the outer reaches of our solar system.

This object would be different from -- and much closer than -- the so-called Planet Nine, a planet whose existence yet awaits confirmation, according to the study to be published in a forthcoming issue of the Astronomical Journal.

In the paper, Kat Volk and Renu Malhotra of the University of Arizona's Lunar and Planetary Laboratory (LPL) present compelling evidence of a yet-to-be- discovered planetary body with a mass somewhere between that of Mars and Earth.

The mysterious mass, the authors showed, has given away its presence -- for now -- only by controlling the orbital planes of a population of space rocks known as Kuiper Belt Objects (KBO), in the icy outskirts of the solar system.

While most KBOs -- debris left over from the formation of the solar system -- orbit the Sun with orbital tilts (inclinations) that average out to what planetary scientists call the invariable plane of the solar system, the most distant of the Kuiper Belt's objects do not.

Their average plane, Volk and Malhotra discovered, is tilted away from the invariable plane by about eight degrees. In other words, something unknown is warping the average orbital plane of the outer solar system.

"The most likely explanation for our results is that there is some unseen mass," says Volk, a postdoctoral fellow at LPL 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," Volk said.

For the study, Volk and Malhotra analysed the tilt angles of the orbital planes of more than 600 objects in the Kuiper Belt in order to determine the common direction about which these orbital planes all precess. Precession refers to the slow change or "wobble" in the orientation of a rotating object.