While some are obsessed with finding Planet Nine, a group of astronomers have quietly come across a massive discovery of 840 minor planets traveling around the sun in well-defined orbits just beyond Neptune.

Over a period of five years, from 2013 to 2017, researchers involved in the Outer Solar System Origins Survey have been mapping the paths that these 840 icy worlds are taking around the sun. Using the imaging camera of the power Canada-France-Hawaii Telescope in Maunakea, Hawaii, they were able to pinpoint slow-moving pinpricks of light within patches of sky near Neptune and away from the bright star fields of the Milky Way galaxy.

The result? Their discovery has increased the number of objects in the solar system that go around the sun by 50 percent. Out of the 840 little worlds, one of them is Pluto.

Small Planets Have A Big Impact

The new discovery could help us better understand the history of how the solar system took its present shape. When the sun was born, it was circled by a massive disk of material. The disk was eventually pulled out by small planets sitting on its outskirts. This caused the eight big planets to form and settle in their orbits, while the small planets spread out everywhere in the solar system.

"These little icy worlds are important as they help us tell the solar system's history," Michele Bannister of OSSOS writes for The Conversation. "Mapping the minor planet populations that are left over from the disk lets us reconstruct the history of how the big planets were pushed into place."

840 New Worlds To Explore

The 840 planets are divided into two major groups. One group consists of 436 little planets located in the Kuiper belt some 37 to 50 astronomical units (au) from the sun. One au covers the distance between the sun and the Earth. A fraction of these, particularly the planets found between 43 and 45 au have a flat, circular orbit that suggest they were original fragments of Neptune that have since broken off. In January 2019, the New Horizons spacecraft will fly by one of these planets, a world as big as London, giving scientists a closer look at what these icy worlds are like.

The second group consists of 313 small planets located as far out as 130 au. The OSSOS team estimates that there may be 90,000 of these icy worlds, which may have settled into orbit when they encountered Neptune hundreds of millions of years ago. One of these planets is 2015 RR245, a tiny world about half the size of Britain.

Proof Of Planet Nine?

A third group is far rarer and more mysterious than the first two groups. This consists of nine icy worlds that take as long as 20,000 years to travel around the sun. Each planet never comes close to Neptune, which may give rise to the theory that another major planet is lurking just beyond what our astronomers can currently observe.

If such a planet exists, then it may be the one responsible for causing these nine little worlds to cluster in space. However, as Bannister points out, the nine mysterious planets are spread out more evenly, suggesting that a hypothetical Planet Nine could have subtler gravitational influence.

The team at OSSOS has published a paper on their discovery in The Astrophysical Journal Supplement Series.