Once, it was considered that there were 11 planets in our solar system. They were: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Neptune, Uranus, Pluto, Ceres, and Eris. But now, it is considered that there are actually 8 planets (Pluto, Ceres and Eris are considered as dwarf planets) in our solar system. But now, the very interesting thing is, some scientists have jumped into a debate, claiming that Pluto is a planet.
What is the definition of a planet? In simple word, objects that are “large” in size in the space and orbiting the Sun or another star is called a planet. But in August 2006, International Astronomical Union (IAU) voted to update the definition of what makes a planet. According to their decision a planet must satisfy the following three criteria:
- It must be an object which independently orbits the Sun
- It must have enough mass so that gravity pulls it into a roughly speroidal shape
- It must be large enough to “dominate” its orbit (ie. its mass must be much larger than anything else which crosses its orbit
And since then, many astronomers as well as scientists started to deny Pluto as a planet although it orbits the sun. They claimed that Pluto does not qualify to be a planet because it is not as “large” as a planet should be. The same goes for the other two: Ceres and Eris. Now these three (Pluto, Ceres and Eris) are considered as dwarf planets.
But last week, a group of scientists forgathered at the Harvard-Smithsonian Center for Astrophysics to battle out over what actually makes a planet. It is to be noted here that the scientists debated among themselves (two for Pluto being a planet and one against) in front of an audience of scientists, teachers and the public. However, those scientists who still consider Pluto a planet said that Pluto satisfies all the criteria (actually it satisfies the first two criteria completely, but not the third one entirely) for being a planet, and if so, then why it will still be considered a dwarf planet, why not a planet? And then a vote was made where the majority cast their vote for Pluto a planet.
Gareth Williams, associate director of the IAU’s Minor Planet Center, who presented the IAU definition at the Harvard debate said, “In my world, Pluto is not a planet.”
The debate was really really and r-e-a-l-l-y interesting. Here’s the entire video of the debate.