On January 5, 2005, an object was found beyond the orbit of Pluto. It was confirmed that the object now called Eris is larger than the 9th planet.

 

The International Astronomical Union had a meeting in Prague, the capital of the Czech Republic. There, on August 24, 2006, they officially defined the word "planet" for the very first time.

 

The International Astronomical Union defines a planet in this way:

 

1. A planet is a celestial body that is in orbit around the sun.

 

2. A planet is a celestial body that has sufficient mass for self gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium, a nearly round shape.

 

3. A planet is a celestial body that has cleared the neighborhood of its orbit.

 

For more information about the resolution, here is the link:

http://www.iau.org/static/resolutions/Resolution_GA26-5-6.pdf

 

 

 

 

 

 

 

 

 

 

 

 

 

The IAU Solar System

Courtesy of the IAU

 

However, the larger object Eris, named after the Greek Goddess of Discord, was observed to be smaller than Pluto. Observations taken from the Hubble Space Telescope were the source of this information.

 

What the public didn't know about the resolution was that only four percent of the IAU membership attended the meeting in Prague. There are 10,871 members of the IAU, and only 474 members attended!

 

Many astronomers, including Alan Stern, the mission leader of the New Horizons Project, felt that the resolution was "sloppy science" (Universe Today). The organization's main conclusion was that Pluto intersects Neptune's orbit.

 

The IAU also proclaimed that Pluto orbits in a 3:2 resonance with Neptune. Basically, Neptune goes around the Sun three times in the same amount of time that Pluto goes around the Sun twice. These conclusions, explained at the meeting, convinced the IAU to reclassify the 9th planet as a dwarf planet.

 

Go to the "Plutonian Conclusion" page on this website and you'll be convinced that Pluto and maybe even Eris should be planets!

 

.