Astronomers have recently discovered an additional 139 minor planets in our own solar system, far beyond Neptune. Data from the Dark Energy Survey was analyzed to find the new discoveries, and it is expected that this same technique will reveal many thousands more. Researchers are hopeful that all of this data will provide new clues towards locating a theoretical Planet Nine on the outer fringes of the Solar System.
The eight planet, Neptune, orbits the sun at an average distance of 30 astronomical units (AU). For those unfamiliar, an AU is roughly the distance from Earth to the Sun and equal to about 150 million kilometres (93 million miles). However, that distance varies as Earth orbits the Sun, from a maximum (aphelion) to a minimum (perihelion) and back again once a year. Originally conceived as the average of Earth’s aphelion and perihelion, since 2012 it has been defined as exactly 149,597,870,700 meters. Beyond Neptune lies the Kuiper belt, the comet-rich area of icy and rocky worlds (including Pluto) that overall is dozens to hundreds of times more massive than the asteroid belt between Mars and Jupiter. Both within the Kuper Belt as well as beyond its outer edge at 50 AU from the sun, orbit what are knows as trans-Neptunian objects (TNOs). We currently have cataloged almost 3,000 TNOs, but some estimates put the total number close to 100,000.
As more TNOs have been located over the years, some astronomers have noticed that a group of these objects have strange orbits that cluster up in unexpected ways. It’s the sort of patterns that would emerge thanks to the influence of a larger planet. This is why some researchers believe that this points towards the existence of an massive and yet undiscovered 9th planet that could be up to 15 times the mass of the Earth orbiting 400 AU from the Sun.
So far the evidence for another planet has been pretty indirect and thin. These strange orbits could end up being the result of something else, or they could just be coincidental. Finding more TNOs beyond the Kuiper belt is the next step in finding additional evidence towards or against the existence of a 9th planet.