NASA scientists have just proposed a new definition for planets, and this is great news for little Pluto! If this new definition, which you can consult in this document, is approved, will not only take Pluto to the Planet class again, but will also do the same for more than 100 other celestial bodies in our Solar System, including our own Moon!
The base for this change, and the one the team hopes to get approval for, is that to be considered a planet, the celestial body no longer needs to be orbiting the Sun, instead we should only take in account the physical properties and not their interactions with stars.
“In keeping with both sound scientific classification and peoples’ intuition, we propose a geophysically-based definition of ‘planet’ that importantly emphasises a body’s intrinsic physical properties over its extrinsic orbital properties”, explained the team led by Alan Stern, principal investigator of NASA’s New Horizons mission to Pluto.
Back in 2006, Pluto was ‘demoted’ to dwarf planet, in result of a rewrite of the definition of planets. Here is the definition of a planet in our Solar System by the International Astronomical Union (IAU):
“A celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit”.
Stern, thinks it’s not right to maintain such definition, set by an astronomer, who studies multiple celestial bodies and cosmic phenomena, instead of a planetary scientist, who’s main focus are planets, moons and planetary systems. It’s equivalent to going to a heart surgeon, to treat a toothache.
“Even though they’re both doctors, they have different expertise”, He said. “You really should listen to planetary scientists that know something about this subject. When we look at an object like Pluto, we don’t know what else to call it”.
So, Stern’s team have written a new definition of a planet to be submitted to the IAU for consideration, which states:
“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”, and if you want a simpler version of it, it’s something like, round objects in space that are smaller than stars.
Although it seems like a rather vague definition, it’s enough to cover only the intended celestial bodies, and it’s based on the physics of the world itself, instead of its interaction with external objects.
This new definition, if accepted, would turn Pluto back into a planet, but also many moons including our own companion. One giant problem with the present definition, is that it only applies to Our own Sun, meaning that all other planets in other Solar Systems and Galaxies, are not considered Planets.
Although IAU still needs to approve the newly proposed definition, we are looking forward to it, so we can have our old friend Pluto back in the Planet category.