‘Happy’ Pluto Demotion Day

When Pluto was first discovered in 1930, the news that there was a ninth planet in the solar system was exciting, groundbreaking, and eventually came to be taken for granted. But on August 24, 2006, a mere 76 years after its discovery, Pluto was “demoted” to the status of dwarf planet by astronomers at the International Astronomical Union (IAU).  

To say that the public was upset about this reclassification of the underdog celestial body would be an understatement, but armchair astronomers weren’t the only dissenters. According to Dr. Alan Stern, planetary scientist and head of National Aeronautics and Space Administration’s New Horizons mission which explored the Pluto system six years ago and is now exploring further out, the IAU’s narrowed definition of a planet was a result of their horror over “the idea that there could be hundreds of small planets beyond the orbit of Neptune in the Kuiper Belt” in our solar system.  

Pluto is one of many small, icy planets in a region of the solar system called the Kuiper Belt which consists of a huge cluster of objects orbiting our sun in a donut shaped mass at the edge of the known solar system, sculpted by the gravitational forces of massive gas giants Neptune and Uranus. Planets in the Kuiper Belt “now outnumber the terrestrial and gas planets, and are expected to number in the hundreds when surveys are complete,” according to Stern.  

Based on the classification used by planetary researchers, all so-called dwarf planets are also, in fact, planets. This includes Pluto as well as others in the solar system like Eris, Makemake, Ceres, and Haumea. Stern claims that to separate planets — defined as bodies orbiting the sun and having enough mass to maintain a round shape but insufficient mass to trigger nuclear fusion at the core — from dwarf planets — which have not “cleared their neighborhood” allowing them to be the only planet on the block — is unnecessary and not scientifically relevant.  

So, there is still some debate in the scientific community about whether to consider Pluto a full-fledged “planet.” In any case the celestial body is fascinating. As NASA says “Pluto is a complex and mysterious world with mountains, valleys, plains, craters, and maybe glaciers.”  

Pluto’s Composition  

The eight “main” planets of the solar system are of two particular varieties: terrestrial planets composed primarily of silicate rocks or metals (Mercury, Venus, Earth and Mars,) and gas giants composed mostly of massive amounts of hydrogen and helium (Jupiter, Saturn, Uranus and Neptune.)  

Pluto, however, is what can be known as an ice planet or a “small icy world,” which are planets made up of frozen and icy volatiles. Pluto is composed of frozen nitrogen, methane, and carbon monoxide.  

Pluto’s Partnership  

Pluto has five known moons, but its largest, Charon, is approximately half the size of the planet it orbits. This unique configuration means that Pluto and Charon actually orbit each other. While a traditional world/moon system, like Earth and our moon, has a center of orbit and thus a center of mass inside the planet, the center of Pluto and Charon’s orbit lies in the space between them. For this reason, Pluto and Charon are sometimes called a “double planet.”  

Pluto’s Vision Into Kuiper  

One thing that is certain about Pluto’s status is that it is a large, close, standout example of a Kuiper Belt Object. And its icy, planet-ish properties and strange orbital pattern can offer insight into even more of the icy debris at the edge of known space. As astronomers and planetary scientists alike venture further out into the cosmos, there is a lot to be learned about the furthest reaches within our grasp.  

This strange rock in space, although controversial, is a unique, fascinating and enlightening vision, and an exciting reminder of all that we still have yet to discover — even within the bounds of our own solar system. 

By Ardea C. Eichner