Scientists have postulated the existence of possibly two undiscovered planets beyond the orbit of Neptune to explain discrepancies in the orbits of trans-Neptunian objects (ETNO). The objects have orbits that take them beyond the orbit of the planet Neptune.

Theory predicts that they be randomly distributed and that their orbits must have a semi-major axis with a value around 150 AU; an orbital inclination of nearly zero degrees; and an angle of perihelion, the in the object’s orbit at which it closest to the , of zero to 180 degrees.

However, a dozen ETNO do not these orbital criteria. These objects have semi-major axis values of 150 to 525 AU, orbital inclinations of around 20 degrees, and angles of perihelion far from 180 degrees.

According to a statement, a study by astrophysicists at the Complutense University of Madrid (UCM) and University of Cambridge have calculated that these orbital discrepancies could be explained by the existence of at least two additional planets beyond the orbits of Neptune and dwarf planet Pluto. Their study suggests that the gravitational pulls of those two planets must be disturbing the orbits of some smaller ETNO.

However, there are two with the hypothesis. One is that current models of the formation of our solar system do not allow for additional planets beyond Neptune. Secondly, the team’s sample size is very small, only 13 objects. However, additional are in the pipeline, which will expand the sample.

“This excess of objects with unexpected orbital parameters makes us believe that some invisible are altering the distribution of the orbital elements of the ETNO and we consider that the most probable explanation is that other unknown planets beyond Neptune and Pluto,” said Carlos de la Fuente Marcos of UCM and lead author on the study.

The new findings have been published in two papers published in the journal Monthly Notices of the Royal Astronomical Society Letters.