|On August 24, 2006, the International Astronomical Union (IAU) decided Pluto would no longer hold planetary status. The decision by the IAU identifies the basic properties celestial objects will have to have before they can be considered planets. |
The new definition for a planet has been 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 ... nearly round shape, and has cleared the neighborhood around its orbit." For now, there will be eight planets in our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Pluto is automatically disqualified because it has not cleared the neighborhood around its orbit. Pluto is in an area known as the Kuiper belt which contains many other objects the size of Pluto in this same area.
Instead, Pluto will be reclassified in a new category of "dwarf planets," similar to what long have been termed "minor planets." The definition also lays out a third class of lesser objects that orbit the sun -- "small solar system bodies," a term that will apply to numerous asteroids, comets and other natural satellites.
The decision at the IAU conference of 2,500 astronomers from 75 countries was a remarkable shift from previous discussions, when the group's leaders suggested a proposal that would have reaffirmed Pluto's planetary status as well as made planets of its largest moon and two other objects. That plan proved highly unpopular and led to days of debate, leading to Pluto's reclassification.
Now two of the objects that could have come out of this conference as confirmed planets will join Pluto as dwarfs: the asteroid Ceres, which was a planet in the 1800s before its status changed to an asteroid; and 2003 UB313, an icy object slightly larger than Pluto whose discoverer, Michael Brown of the California Institute of Technology, has nicknamed "Xena." Charon, the largest of Pluto's three moons, is no longer under consideration for any special designation.
This decision is quite controversial, changing the classification of our planets that we have known for the past 76 years. Do you think Pluto should be still considered a planet? Do you agree with the development of smaller classifications of planets? Share your thoughts in the Opinion Corner forum.
|Image of Pluto. Image credit: NASA.|
|Pluto, center and it's previously known moon Charon, below Pluto and right of center, shine brightly. Two more moons appear more faintly to the right of the pair. Image credit: NASA.|