The search for a possible ninth planet of the solar system has yet to turn up any hard evidence, but one team of scientists has uncovered compelling clues. Researchers at the University of Arizona (UA) say that their analysis of an unusual orbital arrangement suggests that it can be explained by the presence of the so-called "Planet Nine."

Back in January, Caltech planetary scientists Konstantin Batygin and Mike Brown claimed that they had proof of the existence of a celestial body they referred to as Planet Nine. They were not talking about making any direct observations of it. Batygin and Brown used mathematical modeling and computer simulations to determine that the putative planet could be orbiting in the far reaches of our solar system - 20 times the distance of Neptune from the Sun.

"Although we were initially quite skeptical that this planet could exist, as we continued to investigate its orbit and what it would mean for the outer solar system, we become increasingly convinced that it is out there," said Batygin on the Caltech news blog. Their calculations showed that Planet Nine could account for a highly implausible alignment in the orbits of six distant minor planets.

The six bodies are traveling in elliptical orbits which all point in the same spatial direction. The odds that all of the six would possess the same orbital tilt is very small, about 0.007 percent, noted Brown on the same blog posting.

An independent team at UA, comprising scientists Renu Malhotra, Kathryn Volk and Xianyu Wang, analyzed the orbital characteristics of the same six minor planets. Reporting their findings in the Astrophysical Journal Letters, the authors highlight the unusually close synchronization of the bodies' orbital periods.

The synced orbital periods of the six bodies strongly indicate some kind of gravitational link between them. But these minor planets are lacking the mass to have that degree of gravitational effect on one another. It's much more plausible that some larger unseen object is responsible for the gravitational influence - such as a massive planet around the size of Neptune.