Our Solar System May Have Two Undiscovered Planets

On the outer reaches of our solar system, well past Neptune and Pluto, lurk dozens of asteroids and possible minor planets, dimly lit by the faint glow of our sun. Last week, that strange place got even stranger.

On January 13, scientists from the University of Madrid and the University of Cambridge announced that the eccentricities of some of the farthest objects might be explained by the gravitational pull of two large bodies—in other words, undiscovered planets.

ETNOS jpl caltech image
New calculations suggest that two undiscovered planets may lurk at the edge of our solar system.

The team faces an uphill battle to add them to our solar system’s familiar roster. David Wilson, writing for Astrobites, urges caution:

The calculations suggesting the existence of unseen planets is based on observations of only 13 KBOs [Kuiper Belt Objects], few enough that the clustering could be down to simple chance. If future observations find many more KBOs that don’t fit the pattern, then the case for missing planets will disappear. If, on the other hand, they do match what has already been seen, then their behaviour could be used to narrow down the locations of the unseen super-Earths, giving future astronomers the information they need to find them.

The authors of the study—who published their results in two papers, one just this month, and an earlier one in September, in the Monthly Notices of the Royal Astronomical Society—agree that their conclusions are limited by a small sample size, but conclude their earlier paper with the argument that “the same trends are found for asteroids and comets,” and their results are unlikely to be due to Neptune’s gravitational pull or to observational bias.

Fortunately, this all may be sorted out by the New Horizons spacecraft, which is scheduled to buzz Pluto this summer. The data it beams back could shed light on these mysterious gravitational forces.