In the early 1600s Galileo discovered the four largest moons of Jupiter. This discovery encouraged the study of our Solar System and the objects known today as planets. A planet was a planet because it was distinct: a large body that orbited the Sun. Therefore, up until 2006, there was never a need to define what a planet is because it was indisputable. There was no real need for a formal definition for planets, until the discovery of Eris. Clyde W. Tombaugh discovered Pluto in February 18, 1930. Based on what were the qualifications for being a planet – orbiting the Sun and being sufficiently large – Pluto was obviously a planet at the time. Little Pluto was recognized as the smallest planet in the Solar System and the ninth planet from the sun. However, in 2003 an astronomer saw a new object that surpassed Pluto. This discovery made several astronomers question if the new object, named Eris, was a new planet itself. Eris was discovered in 2003 by a team led by Mike Brown, who determined that this object was 27% more massive than Pluto! This raised several questions, many of which were never presented before. If Eris is not a planet, what makes Pluto a planet? Therefore, the finding of Eris initiated the question, what makes a planet a planet. In 2006 the International Astronomical Union voted on and passed the definition of a planet: an object must meet three criteria in order to be classified as a planet; it must orbit the sun, must be big enough for gravity to squash it into a round ball, and it must have cleared other objects out of the way in its orbital neighborhood. And like that, Pluto was no longer classified as a planet. Bam.
The problem was that Pluto’s orbit is in the Kuiper Belt along with 43 other known objects, which proved that its neighborhood is not sufficiently clear in order to be considered a planet. Thus, after a heated debate, the International Astronomy declared Pluto as a dwarf planet. You may ask, what is the difference between a planet and a dwarf planet? Well it is simple; a dwarf planet is a planetary-mass object that is big enough for gravity to squash it into a round ball, but not big enough to clear its orbit.
However, Pluto’s fame does not end here, because a space probe by NASA was launched in 2006 in order to obtain more information about it. This spacecraft, called New Horizons, will arrive in July 2015 and it is expected to study Pluto and its many moons. This mission will not only provide details about the unknown characteristics of Pluto by astronomical images and collecting scientific information, but the spacecraft will also head deeper into the Kuiper Belt. Pluto will become famous once again. Therefore, looking back on the discovery of Pluto, we must realize that Pluto has truly impacted the way we study and view our Solar System today.
Dalia Dorantes
