In our school text-books we had read that there are nine planets. We all remember their names in increasing order of their distance from the sun. And we know that Pluto is the ninth planet. Well, it was the ninth planet. There has been a change in the planetary situation and we ( or rather I) at VERITAS thought that we must inform you about this change. When Pluto was discovered in 1930 it was added to the list of planets. It’s mass was not accurately known but scientists estimated that it would be of a comparable size to Mercury.In 1978 its moon, Charon was discovered and that made it possible to calculate Pluto’s mass.Pluto is one-twentieth the size of Mercury making it the smallest planet!
Now Pluto did not also behave like other planets. It has a huge orbital eccentricity and high orbital inclination. An orbit has less eccentricity when it is closer to a circle in shape. A more eccentric orbit is more elliptical or elongated. Pluto’s orbit is so elongated that for about 14 years of its 248 year orbit, it is closer to the sun than Neptune. So for 14 years out of its 248 year orbital period it is the 8th planet and Neptunebecomes the 9th. It’s orbit crisscrosses Neptune’s orbit but there will never be a collision between the two planets because their orbits are locked in a resonance( See VERITAS: Resonance in orbits- posted in year 2000. Available on request). Now let me explain what is meant by high orbital inclination.
All planets revolve around the Sun in one plane called the ecliptic. Pluto’s orbit does not lie on its plane – it is inclined by 17 degrees. So it does not behave like other planets and that had caused astronomers a lot of embarrassment. And to make matters worse, astronomers detected a few “objects” in the solar system which were of a comparable size or even larger! Eris, for example, islarger than Pluto. So should these other objects be included in the list of planets or should Pluto be expelled from the list?
To resolve the issue, the International Astronomical Union( IAU) decided to make a set of criteria that an object must satisfy in order to be given the planet status. So an object is called a planet if it satisfies the following:
1) It should revolve around the sun( and not around any other object)
2) It should have enough mass for gravity to squeeze it into a sphere. In scientific language this is called “achieving hydrostatic equilibrium”.
3) It should have cleared its neighborhood i.e it should have captured all nearby objects or collided with them so that there is nothing else left in the neighborhood of its orbit.
If an object only meets criteria 1 and 2 i.e. it revolves around the sun and is spherical because of its own gravity but has not cleared its orbital neighborhood then it is classified as a dwarf planet.
And if you go by the above criteria, then Pluto is a dwarf planet. It revolves around the sun and is spherical in shape due to its own gravity but has not cleared its orbit’s neighborhood. We know that it has not cleared it’s orbit’s neighborhood because it shares its orbital neighborhood with several other objects in a ring or belt beyond Neptune. This ring/belt of objects is called the Kuiper belt. There are hundreds of small objects in the Kuiper belt and Pluto is one of them. The Kuiper belt is also the source of many comets. So Pluto has not cleared its orbit and is therefore a dwarf planet.
So Pluto is one of the five dwarf planets identified so far. The following is the complete list:
1) Pluto ( A Kuiper Belt object)
2) Ceres ( a part of the asteriod belt between Mars and Jupiter)
3) Haumea ( Kuiper Belt Object)
4) Makemake ( Kuiper Belt Object)
5) Eris ( A scattered Disk object. The scattered disk is beyond the Kuiper Belt and is the source of lots of comets. Eris is the largest dwarf planet) So Pluto has been demoted from the status of planet to dwarf planet. The word “plutoed” or “to pluto” was coined in 2006 following Pluto’s demotion. “To pluto” means to “demote or devalue something or someone”. Therefore we can say that Pluto has been plutoed.
Go, wondrous creature! mount where Science guides:
Go, measure earth, weigh air, and state the tides:
Instruct the planets in what orbs to run,
Correct old time and regulate the Sun;
Tags : Universe, Unearthly, Pluto, 2010 VERITAS