Evidence Mounts For The Existence Of Planet Nine

Artist's impression of Planet Nine. NASA

Two new studies have been published providing fresh evidence for the existence of a massive planet at the edge of the Solar System.

The object, dubbed Planet Nine, was first proposed early this year, but it has yet to be directly observed. It is believed to be on average 70 times more distant from the Sun than Earth, so observations are difficult.

So far, astronomers have looked at other potential effects this object might have on the Solar System. Now, researchers from the California Institute of Technology (Caltech), including the proposers of Planet Nine – Mike Brown and Konstantin Batygin – suggest that the six-degree tilt observed in the Sun compared to the plane of the Solar System is actually caused by the pull of Planet Nine.

"Because Planet Nine is so massive and has an orbit tilted compared to the other planets, the Solar System has no choice but to slowly twist out of alignment," said lead author Elizabeth Bailey in a statement.

The first paper, available online and submitted to the Astrophysical Journal, focuses on the angular momentum contribution of the potential planet on the spin of our star. Planet Nine is believed to arrive as close as 200 AU and as distant as 1,200 AU, with 1 AU (astronomical unit) being the Earth-Sun distance.

Having an object at least 10 times the mass of Earth, on such a wide orbit, and with an expected inclination of 30 degrees will generate a wobble in the Sun. And according to the calculations, it can explain the observed tilt.

The other study, published in the Astrophysical Journal Letters, focuses on a different piece of evidence. It appears that the orbit of four minor objects in the Kuiper belt, including the minor planet Sedna, are not random. The cause of this cosmic ballet seems to be a massive object with properties very similar to what is expected for Planet Nine.

"We analyzed the data of these most distant Kuiper Belt objects, and noticed something peculiar, suggesting they were in some kind of resonances with an unseen planet," lead author Renu Malhotra, from the University of Arizona, said in a statement. "Our paper provides more specific estimates for the mass and orbit that this planet would have, and, more importantly, constraints on its current position within its orbit."

Neither pieces of research are conclusive evidence for the existence of Planet Nine, but the scale is tilting in its favor. Brown and his colleagues are now searching the outer Solar System for signs of Planet Nine, and think it may take three or more years to finally observe it.

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