KILEIGH FORD — We grew up with nine planets; the ninth, and furthest out in our solar system, only lasted as a planet for 76 years. Hearts were broken in 2006 when Pluto was declassified as a planet, but some astronomers are still pushing for Pluto to make a comeback.
In August of 2006, 426 astronomers voted at the International Astronomical Union meeting to demote Pluto from planethood. Through this, the IAU created three criteria to develop a standard for planethood.
Firstly, the body must orbit the sun on its own accord, meaning moons are ruled out since they orbit a planet that orbits the sun.
Secondly, the planet candidate must have enough mass for its gravity to be able to create its spherical shape.
Lastly, and most controversially, it must “clear the neighborhood around its orbit,” which means it must be much larger than anything around it in order to move them out of its orbital path.
According to Space.com, clearing the neighborhood is where Pluto fell short of planethood as it resides within the Kuiper Belt, which is a region past Neptune’s orbit full of icy bodies of comets, meaning it is nowhere near cleared.
Currently, Pluto is classified as a dwarf planet, a planet that does not adhere to all of the criterion to be a planet.
The definition of a dwarf planet, according to the IAU, is a celestial body that orbits the sun, has a great enough mass for its gravity to create its spherical shape, does not “clear the neighborhood around its orbit,” and is not a satellite.
Another problem, as reported by Space.com, lies with Pluto’s orbit, or path taken around the sun.
All of the planets in our solar systems follow a rounded, ellipse-shaped path for their orbit.
These paths make up a sequence of concentric rings that do not cross over one another. Pluto, however, the furthest planet from the sun, has a very wide orbit that crosses over the eighth planet, Neptune’s, orbit and nearly Uranus’. It is seen as abnormal compared to the other eight planets’ orbits.
New fights are on the horizon though. Recently, Alan Stern, a lead investigator of NASA’s New Horizons mission, and David Grinspoon, a planetary scientist, have published Chasing New Horizons: Inside the Epic First Mission to Pluto, detailing the Pluto flyby mission.
In addition, the Washington Post has published a perspective piece, “Yes, Pluto is a Planet,” written by the two where they detail the IAU’s problematic criterion for planethood and ridicule their quick decision to dub Pluto a dwarf planet.
They point out, “This criterion is imprecise and leaves many borderline cases, but what’s worse is that they chose a definition that discounts the actual physical properties of a potential planet, electing instead to define ‘planet’ in terms of the other objects that are — or are not — orbiting nearby.”
They go on to point out that, by this criterion, you can put any planet in our solar system in an asteroid belt and it will fail to continue on being a planet, just like we have encountered with Pluto.
Past the discussion of Pluto’s planethood, many other potential planets have been impacted. According to Space.com, Ceres, Haumea, Makemake, and Eris are the other four dwarf planets in our solar system that have been denied planethood based off their erratic orbits or not “clearing the neighborhood around its orbit.”
Makemake is a dwarf planet that would have received planethood status if not for Pluto’s being taken away.
The planethood status of exoplanets, or planets beyond our own solar system, have also been influenced by this criterion, says Mike Wall of Space.com.
Since these planets are not orbiting the sun, as they are outside of our solar system, the first criteria for planethood is not fulfilled, meaning they do not qualify as planets.
The debate rages on.
Diehard Pluto fans will continue to stand up for their beliefs about the planet. They will fight for its planethood and combat the solar system-based criteria for it.
Astronomers aiming to correctly form criteria that will allow for classification of heavenly bodies, based on the differences between them, will stand their ground.
With new scholarly articles and fierce debates emerging at the forefront, there is hope that our ninth planet could be reinstated someday soon.