Death From Above

Planet Nine

posted on 8/2016   By: Dave Schalek

The word is not “perturbator”; it’s actually “perturbation”. In astronomy, the word refers to the motion of a massive body subjected to forces other than the gravitational attraction of a single, other massive body. Observing perturbations in the orbit of an object in the Solar System usually leads to great discoveries. For example, the planet Neptune was discovered due to perturbations in the orbit of Uranus; that is, Uranus’ motion deviated slightly from its predicted orbit about the Sun in such a way that could be explained by another planet orbiting the Sun further out. That planet was Neptune, and it was discovered to be in the place that is was mathematically predicted to be. The prediction of the existence of and the subsequent discovery of Neptune was a triumph of applied celestial mechanics.

Perhaps recent headlines heralding the existence of the long sought “Planet X” (well, “Planet Nine” is a better moniker due to Pluto’s well deserved demotion) may turn out to be another triumph of applied celestial mechanics. To explain, think of the Solar System as regions, or zones, where the objects in each region are made of the same material. Outwards from the Sun, the first of these regions is made up of Mercury, Venus, the Earth and its Moon, Mars, and the asteroid belt. These objects are generally made of the same stuff, namely, rocks and metals. Moving outwards, the gas giants Jupiter and Saturn are rocky cores surrounded by huge envelopes of hydrogen and helium, gases that would be too volatile to gather around a rocky core in the inner system close to the Sun.

Jupiter and Saturn each possess an enormous retinue of moons and moonlets, fascinating worlds in their own right, all, more or less, made of rocks and water ice. The ice giants, Uranus and Neptune, are next, smaller worlds than Jupiter and Saturn that have colder gases such as ammonia making up their atmospheres, as well as hydrogen and helium. Each comes with its own retinue of moons and moonlets made of rocks and water ice.

Outwards from the orbit of Neptune, the rock and ice debris that is leftover from the formation of the Solar System falls into two regions. First is the Kuiper Belt, a disk of material extending about 50 A.U. from the Sun (one A.U., or astronomical unit, is the distance from the Earth to the Sun). Pluto is a member of the Kuiper Belt as are the lesser known ice dwarf worlds of Eris, Quaoar, and Makemake. The Kuiper Belt is also the source of what are called short period comets with Halley’s Comet being the most famous example.

Even further outwards is a sphere of water ice and rocky debris called the Oort Cloud, perhaps extending out about half a light year from the Sun. We know that the Oort Cloud is there for technical reasons involving what are called long period comets. Comets Hale-Bopp and McNaught originated in the Oort Cloud, for example.

I mention all of this because of a few peculiar objects that have recently been discovered in a sort of no man’s land in between the Kuiper Belt and the Oort Cloud. The most well known of these objects is Sedna, which was discovered in 2003, and was originally thought to be a member of the inner Oort Cloud, taking 11,400 years to orbit the Sun.

Now, astronomers are not so sure due to the recent discoveries of about a half dozen or so other objects in this same region of space beyond the Kuiper Belt. What’s interesting about all of these objects is the similarity of their orbits. Each orbits the Sun in an ellipse that dips below the plane of the ecliptic (the orbital plane of all of the planets and the Kuiper Belt) by about 30 degrees. What’s more, the objects’ points of closest approach to the Sun (called the  perihelia) all cluster together at virtually the same point in space. The statistical odds of this curious alignment randomly happening is about 0.007%, according to detailed calculations. However, each of these objects could have been gravitationally perturbed into these similar orbits over a long period of time by a large planet orbiting the Sun much further from the Sun than Neptune; that is, the long sought Planet Nine.

The first graphic below shows the current location of Sedna and one of the other objects in relation to the Kuiper Belt and the remainder of the Solar System.

The second graphic illustrates the orbits of Sedna and the other objects, as well as that of the calculated orbit of the hypothetical Planet Nine.

The mathematical evidence for Planet Nine’s existence, though circumstantial, is, nonetheless, convincing. The problem is that we don’t really know where it would currently be in its orbit, so, actually finding it in a telescope is going to take time and effort.

I listened to Uncanny Valley by Perturbator while contemplating the existence of Planet Nine. I invite you to do the same. Perhaps the album will be on the stereo of future explorers’ spacecraft as they approach the world.