Plutos Demotion
On 24 August 2006, About 2,500 scientists met in Prague for the International Astronomical Union's (IAU) annual general assembly. The IAU is the organisation responsible for making all the important decisions in the astronomical world. This year was no exception, with one of the largest and most debated topics on the Agenda Is Pluto a Planet.
On 24 August 2006, About 2,500 scientists met in Prague for the International Astronomical Union's (IAU) annual general assembly. The IAU is the organization responsible for making all the important decisions in the astronomical world. This year was no exception, with one of the largest and most debated topics on the Agenda "Is Pluto a Planet".
Since Pluto's discovery in 1930 by the American astronomer Clyde Tombaugh, several objects have been discovered that are substantially larger than Pluto, but have not been considered planets, and since there is no actual scientific definition of a planet, there was much confusion over the matter.
New Discovery
In 2003, astronomer Michael Brown of Mount Palomar Observatory, discovered an object outside Plutos orbit and calculated that its size to be greater than Pluto. It had not been discovered before as it orbits at an irregular angle to the solar plane. Since this object is larger than Pluto, and has its own moon (Gabrielle) the surely this must be the tenth planet? Astronomers were divided upon the matter.
Arguments
The two arguments for the case are:
- Ceres, UB313 (Xena), Charon, 2005 FY9, Sedna and Quaoar are NOT planets, therefore Pluto CANNOT be a planet either.
- Pluto IS a planet, therefore about another 11 objects also class as a planet, bringing the total to 20.
Since nobody can agree on what classes as a planet, the IAU were called upon to create a definition. The IAU have been responsible for naming planets and its mission is to "promote and safeguard the science of astronomy in all its aspects through international cooperation."
The Definition
The IAU came up with a definition of a planet as follows:
A planet is a celestial body that:
- Is in orbit around the Sun
- Has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium
- Has cleared the neighbourhood around its orbit.
The definition they decided on rules out Pluto as a planet, and Pluto was officially demoted to a dwarf planet.
The revised Solar System
The IAU's initial proposal was to raise the number of planets in the Solar System to 12, adding the asteroid Ceres, Pluto's "moon" Charon and the distant Xena, but that was met with strong opposition.
After a week of debating, the vote was passed and will rewrite every science book published in the 20th century, the IAU have ruled that Pluto is NOT a planet, but instead a dwarf planet in the Kuiper Belt.
Controversy
1. In orbit around the sun
Pluto orbits the sun, as does Sedna, Xena and Charon.
2. Hydrostatic Equilibrium
Basically this means that the objects mass is great enough that its spinning momentum forms a spherical shape, ie a round object. Pluto is round, as is Ceres, Sedna, Xena and Charon.
3. Clearing the Neighbourhood
The most ambiguous part of the definition is that it should have cleared the neighbourhood around its orbit. Dr Alan Stern of NASA commented "since neither Earth, nor Mars, nor Jupiter, nor Neptune have entirely cleared their regions of debris, none could properly be considered planets."
Final Decision
The IAU have the final say in the matter, and at current the ruling stands.
There are now officially EIGHT planets in the solar system, which are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
In January 2006 NASA launched its unmanned New Horizons probe to Pluto on a mission to learn more about the planet at the end of the solar system. Now it is on a mission to an "unplanet". It is due to rendezvous with Pluto in 2015.
