Pluto used to be the ninth planet, but it lost that distinction several years back. It became the first of many dwarf planets in the outer reaches of the solar system, but there’s a hint something larger may lurk out there. Scientists have been on the hunt for a true ninth planet since 2014, and a pair of new studies provide more evidence that such an object exists.
The Kuiper Belt exists in the space out past the orbit of Neptune, so Pluto and the other objects in this region of space are often called Kuiper Belt Objects (KBO). While studying the orbits of KBOs discovered in recent years, astronomers Michael Brown and Konstantin Batygin of Caltech realized there was an unusual clustering or orbits. According to the 2014 paper, this suggests the existence of a super-Earth body in the outer solar system.
Thus far, no one has been able to turn up direct evidence the so-called “Planet Nine” exists, but the new studies add weight to the hypothesis. Fred Adams from the University of Michigan believes that Planet Nine will be spotted within the next 10 to 15 years. In his latest study, Adams used computer models of the solar system’s evolution to simulate how Planet Nine might fit into our little corner of the universe.
According to Adams, the analysis suggests that Planet Nine is smaller and closer to the sun than previously thought. The team’s model predicts Planet Nine is about five to ten times as massive as Earth and orbits approximately 37 billion miles (60 billion kilometers) away. That estimate makes sense, as astronomers have detected similarly sized planets in other solar systems, but there aren’t any among the known planets here.
Another study from Brown and Batygin examines what we know of the clustered KBO orbits. The researchers looked for bias in each observation, finding a one in 500 chance the observations were inaccurate.
That points to something causing KBOs to organize into these skewed orbits. Other teams have suggested the cumulative gravity from many small objects could affect orbits like this. Still others say a massive object like a brown dwarf grazing the solar system could nudge KBOs into such orbits. For now, the answer is unclear, but the new studies support the idea that Planet Nine exists.