Demoted to dwarf planet status in 2006, Pluto may soon regain its original designation.
A group of NASA scientists has submitted a proposal to the International Astronomical Union (IAU) seeking a reshaping of the characteristics that define a planet. If approved, the new definition would have major consequences for how we classify objects in our solar system.
keeping with both sound scientific classification and
peoples’ intuition, we propose a geophysically-based
definition of 'planet' that importantly emphasizes a
intrinsic physical properties over its extrinsic
orbital properties," the researchers state.
In 2006, the IAU ratified a planetary definition that only includes objects that orbit the sun, have a nearly-round shape, and have cleared the neighborhood around its orbit.
The group proposing changes to this definition is being led by Alan Stern, the principle investigator of NASA's New Horizons mission to Pluto. After the spacecraft's historic flyby in the summer of 2015, scientists expressed amazement at the complex and unique features of the dwarf planet.
“We were just dumbfounded by what a wonderland it is scientifically,” Stern told Business Insider in 2015. He added that Pluto "qualifies in every respect" for planetary status and that the current definition is completely "bogus."
What Stern and his colleagues are proposing, however, wouldn't just right a perceived wrong with Pluto, but would also elevate as many as 110 other objects in our solar system to planetary status.
"We propose the following geophysical definition of a planet for use by educators, scientists, students, and the public," they write. "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."
In other words, if it's round and smaller than a star, it's a planet. This would include our moon, the moons of many current planets, and other objects extending as far out as the Kuiper Belt. The scientists freely admit that this issue presents a dilemma for students attempting to learn the names of planets, but there's a way around that.
analogy, there are 88 official constellations and 94
naturally occurring elements, yet most people are content
to learn only a few," they write. "So it should be with planets."
As for the requirement that a planet's orbit should be free of foreign bodies, the scientists argue that no planet can satisfy this rule because "small bodies are constantly injected into planet-crossing orbits." If Earth were to exist at the same distance as Pluto, for example, this very rule would disqualify it as a planet due to the much larger zone it would need to clear.
"I think the public will take one look at this and they’re going to feel like the IAU made fools of themselves," Stern told Lights in the Dark. "I don’t know a single planetary scientist – out of thousands – I don’t know a single one who says that the IAU decision was a good one."
Whether we keep eight or expand to 110 planets will likely be up for debate when the next General Assembly of the IAU meets in August 2018 in Vienna.