Rick Robinson

Jun 12th 2020

Where Is Planet X?


Dimly lit by a far distant sun, a planet much larger than Earth may orbit in the vast outer reaches of the solar system, eluding our telescopes for more than 400 years. But its presence may leave telltale traces. And as new and more powerful probes join our space exploration armada, even the immensity of space may no longer afford Planet X a hiding place.

So, where is Planet X? The evidence remains circumstantial. The outer reaches of the solar system are a frontier that we are only just beginning to explore.

We can, however, confidently pass on one piece of good news from Planet X, if it exists, has nothing to do with the so-called Nibiru cataclysm, a long-running tabloid media story about a giant planet on a supposed collision course with Earth.

The Killer Planet

Nibiru’s origin came from a 1976 book of amateur speculation about ancient Sumerian astronomy. A few years later, a self-described mystic claimed that this planet — which Sumerian astronomy experts never heard of — was headed for a collision with Earth. That was enough to launch a hundred tabloid stories about the Nibiru cataclysm. But if Nibiru existed, says, it should be easily visible in a small telescope, yet no astronomer has seen any hint of it.

Where Is Planet X? The Long Search for a Distant World

The search for a Planet X is not new. reports that the hunt for a giant outer planet goes back more than 100 years. In 1930, the search led to the discovery of Pluto, which turned out to be much too small to cause the gravitational effects then attributed to Planet X.

The search for new giant outer planets went on the back burner for a few decades. Meanwhile, new discoveries showed that the space beyond Neptune was far from empty. Pluto turned out to be simply one of the largest and closest members of the Kuiper belt, a host of objects ranging from dwarf planets downward.

New discoveries continue to push outward the limits of the solar system. Last year, Carnegie Science reported the discovery of an object, designated 2015 TG387, on an elongated orbit that extends out to approximately 0.03 light-years from the sun.

But 2015 TG387 doesn’t just push the frontier outward. Its orbit — along with the orbits of other newly discovered mini-worlds at the edge of the solar system — shows some distinctive and curious patterns. Their orbits, as Sky & Telescope reports, are similarly aligned in space, with “argument of perihelion” close to either zero or 180 degrees.

Circumstantial Evidence

This sort of alignment does not happen by accident. It suggests that some force is tugging on all of these distant objects. The only real question, according to CNET, is what the force is — whether it is best explained by a single giant planet, or may point instead to the influence of a disk formed by many smaller bodies orbiting the sun.

Getting back to the real outer solar system, even if the culprit is a single giant planet, says Sky & Telescope, there are differing theories about how large and massive the planet may be, and how far it orbits from the sun. One view argues for a Neptune-sized planet, about 10 times Earth’s mass, orbiting up to 100 billion kilometers from the sun.

A competing model suggests that the evidence points to a somewhat smaller world, about five times Earth’s mass, orbiting “only” a few hundred times farther out than Earth. In this case, as CNET notes, the planet is probably a massive rocky planet, a “super earth,” rather than a gas giant like Neptune — a world unlike any of the known solar planets.

The only sure way to settle these arguments once and for all is to go out and discover Planet X. Or else explore the outer solar system so thoroughly as to rule it out.