Pluto’s Comeback? Scientists Propose New Definition for Planets That'll Make Pluto One Again

Pluto recently rang in its 87th birthday since its discovery. As a late birthday present to the far-flung former planet, a group of scientists from NASA recently put together a proposal to redefine what being a planet means. If approved, this move will add over a hundred planets into the solar system including Pluto and our moon.

Led by Alan Stern of NASA's New Horizons mission to Pluto, the team of scientists proposed that planets no longer need to orbit the Sun to be classified as such. According to a report from Science Alert, they plan to define planets with their "intrinsic physical properties" instead of their relationship with stars and other external objects.

The proposed new definition of a planet, according to the team is: "A planet is a sub-stellar mass body that has never undergone nuclear fusion and that has sufficient self-gravitation to assume a spheroidal shape adequately described by a triaxial ellipsoid regardless of its orbital parameters."

More succintly -- and simpler for students -- the scientists consider planets to be "round objects in space that are smaller than stars." With this definition, it's not just Pluto that will make it into planet territory but hundreds of other celestial bodies including the Earth's moon and other moons.

The scientists called the current International Astronomical Union (IAU) definition of planets as flawed, citing three primary reasons for this conclusion.

First, the team criticized IAU for only recognizing objects that orbit the Sun as planets. They also point to "zone clearing" as an unnecessary requirement that no planet can actually satisfy because of other cosmic bodies such as near-Earth objects (NEO) constantly entering and crossing the orbits. Most importantly, the team pointed out that zone clearing is flawed in the way it requires larger objects as it reaches further zones. The scientists explain in the report, "For example, even an Earth-sized object in the Kuiper Belt would not clear its zone."

Time will tell if IAU accepts the proposed planet classifications, but if it pulls through, it's going to be much harder to keep track of Earth's neighboring planets in the solar system.