For many of us Pluto has long been known as the ninth planet in our solar system. Since its accidental discovery, Pluto has always had some unanswered questions but only recently has there been considerable controversy about the classification of Pluto.
We know that Pluto was classified as the ninth planet shortly after its discovery. However, 75 years later on August 24, 2006, the International Astronomical Union (IAU) decided on what the official definition of a planet would be and Pluto did not make the cut. Instead, Pluto was demoted to the status of “dwarf planet.” It is still in the same class as a planet but there are some key differences.
Below we see the distinctions that designate what is and what is not a planet according to the International Astronomical Union:
A “planet” is 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.
A “dwarf planet” is 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, (c) has not cleared the neighborhood around its orbit, and (d) is not a satellite.
All other objects except satellites orbiting the Sun shall be referred to collectively as “Small Solar-System Bodies”.
According to the new rules, Pluto did not meet the criteria. Although Pluto does in fact orbit the Sun, and it is big enough for gravity to squash it into a round ball, it has not cleared other things out of the way in its orbital neighborhood. Pluto was not the only “planet” to be downgraded either. The planet 2003UB313 (Eris), which orbits among the icy wrecks of the Kuiper Belt, and Ceres, which is in the asteroid belt, were also downgraded to dwarf planets.
Pluto holds special significance to our solar system for several reasons. Of course any planet whether dwarf or not holds keys to possible life, the study of atmospheres, the differences in climate causes by the distance from the sun, and the list can go on and on. Pluto is special because for many years it was the most distant large mass that astronomers knew about.
Discovered by American astronomer Clyde Tombaugh in 1930, Pluto takes 248 years to orbit the Sun. This in and of itself is magnificent and hints to the incredibly diverse (but still very cold) nature of the atmospheric conditions present on Pluto depending on the years when it is closest and farthest from the sun. Between 1979 and 1999 was when Pluto’s highly elliptical orbit brought it closer to the Sun than Neptune. During this chance period of opportunity, scientists were able to study the rare dwarf planet of Pluto as well as its moon, Charon. Scientists are still anxious to learn more about the farther parts of our solar system and have launched a robotic space flight mission to Pluto (as it is currently impossible to sustain a human crew for the length of time it would take to reach the far away dwarf plant). This mission by NASA is called New Horizons and was launched in January of 2007. If it lands successfully in 2015 (that’s 8 whole years in flight!), it will allow for the study of both Pluto and the Kuiper Belt region.
The significance of Pluto to our solar system is apparent. Although there may not be direct connections between the faraway mass and your everyday life, study of our solar system answers interesting questions about how our own planet works. We are able to see just how amazing it is to have a planet that is so ideal for human life.
Learn more with these Pluto websites.