The search for the distant Planet Nine continues

27 May 2024

Weird stuff is happening out on the remote boundary of the solar system. Beyond the orbit of Pluto. You name it, it’s going on out there. Irregularities. Anomalies. Clustering of apsidal lines. Perihelia. And — saving the best for last — a surprising prevalence of retrograde Centaurs.

These anomalies include the apparent clustering of apsidal lines of long-period trans-Neptunian object (TNO) orbits, the alignment of their orbital planes, the existence of objects with perihelia extending far beyond Neptune’s gravitational influence, the highly extended distribution of TNO inclinations, and the surprising prevalence of retrograde Centaurs. Collectively, these irregularities hint at the existence of a yet-undiscovered massive planet, tentatively named Planet Nine (P9), whose gravitational influence sculpts the outer reaches of trans-Neptunian space (Batygin et al., 2019).

But this is nothing new. Astronomers have been aware of this activity for some time.

Many postulate this weirdness points to the existence of an — as yet — undiscovered, large-ish planet, out beyond the known planets of the solar system. Some incredible distance out beyond the known planets. Planet Nine, if it exists, is thought to be orbiting the Sun at an approximate distance of twenty times that of Neptune to the Sun.

The gravitational influence of Planet Nine, combined with its extreme distance from the Sun, is enough to interfere with what would otherwise be predictable orbits of the numerous TNO objects, of which Pluto is one.

Planet Nine sort of comes along and displaces — sweeps aside, perhaps — these TNOs. While the presence of a larger planet therefore appears to be the logical explanation for the various irregularities and anomalies witnessed in the outer solar system, scientists are yet to clap eyes the elusive body. Or even calculate its position mathematically, for that matter.

If Planet Nine is found, here’s hoping one of Earth’s space agencies dispatches a probe pronto to go and take a good look at it.