Pluto Is Out
Pluto and its satellite Charon (now also a dwarf planet)
The International Astronomical Union (IAU), the world's official body for astronomy, has voted out Pluto in the roster of planets in the solar system. This was a result of the organization's establishment of 3 main categories of objects in the solar system.
(1) 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.
(2) 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.
(3) All other objects except satellites orbiting the Sun shall be referred to collectively as "Small Solar-System Bodies".
1The eight planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
2 An IAU process will be established to assign borderline objects into either dwarf planet and other categories.
3 These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.
Pluto becomes the prototype from which other trans-Neptunian objects (celestial objects that are farther from the sun compared to the planet
So what wrong did Pluto do? Pluto did not clean his room. According to the IAU, planets and dwarf planets share the same characteristics except that planets have cleared their orbits from astronomical debris.
Here are some interesting facts about this development:
1. The name dwarf planet is a misnomer. The IAU's definition of planet excludes them, which is exactly why they are given a different category.
2. Of the almost 10 thousand members of the IAU, only 424 were in the general assembly to vote. This gives ground to some sectors that argue against the IAU's resolution that would rewrite Science and make giant ripples in history and culture.
3. Mike Brown, whose team from Caltech discovered 2003UB313 (a Pluto-sized celestial object which, before the groundbreaking IAU resolution, was on the threshold of planethood together with two others), declares that, although the development was a personal defeat for him and his team, it is scientifically sound and that he welcomes it.
4. Some argue that the difference pointed out by IAU between planets and dwarf planets (clearing the neighborhood of its orbit from astronomical debris) is contentious, saying that Jupiter's and even Earth's orbits are populated as well with debris.
You may want to read more about this development in these links.
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