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Pluto has been demoted to non-planet status in a vote involving 424 professional astronomers who remained for the last day of a meeting of the International Astronomical Union (IAU) in Prague. The demotion of Pluto was due to the new definition of the world ‘planet’ which states - in layman’s terms - that “anything round, orbiting the sun, is not a satellite of another body, and has enough capacity to clear it’s vicinity of other space objects” is a planet. On the other hand, the IAU also defined the new term “dwarf planet” which states that “anything round, orbiting the sun, is not a satellite of another body, BUT DOESN’T HAVE ENOUGH CAPACITY TO CLEAR IT’S VICINITY” should be called a dwarf planet. Pluto fits the “dwarf planet” definition but not the planet definition.

Less planets but more dwarf planets

According to the new definition of the world planet, we now only have Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune as planets. But we have new names to keep in mind as well and they are the dwarf planets. For now, the official dwarf planets are Ceres which is located in the asteroid belt between Mars and Jupiter, Pluto, and 2003 UB313 or Xena which is far beyond pluto. It is not known whether Pluto’s “moon” Charon will also be called a dwarf planet. The confusion with Charon arises from the fact that it doesn’t really orbit Pluto like a satellite would do. Rather, Pluto and Charon orbits a common center of gravity in a merry-go-round like pattern.

Here is the new official definition of planet, as passed on 24 August 2006:

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 neighbourhood 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 neighbourhood around its orbit, and (d) is not a satellite.

Hmmm…

What do I think about this? Well, I think the decision to demote Pluto is a good step towards scientific clarity of what a planet really is. However, astronomers think that the present definition of planet is a bit off-course when it said that a planet should be able to clear its vicinity of other space objects. Why? Because Earth has asteroids labeled as Near Earth Objects (NEO), Mars also has its share of asteroids in its vicinity. Jupiter has its Trojan asteroids which actually cross the orbit of Jupiter in a step-lock manner. In other words, these “planets” were not really able to clear their vicinity of other space objects. In fact, these planets are even in danger of getting hit by these asteroids. Astronomers on Earth for example monitor the NEO’s regularly checking which of them may hit us.

Anyway…

Anyway… I think it’s still a good idea to take a step towards clarifying what is and what’s not. It is a turmoil at start but we will be smooth sailing soon.

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