Astronomers and scientists in August 2006 have decided that Pluto should no longer be classified as a planet.

Sacramento State Physics and Astronomy professor Chris Taylor gave a speech entitled “What the heck just happened to Pluto?” Friday night on the subject.

Taylor said for a body of mass in space to be considered a planet, objects in space have to meet two specific criteria.

Giving definitions from the International Astronomical Union, Taylor said the first definition of a planet is the object’s orbit and gravitational pull has to affect other bodies. The second definition is the body has to be a certain shape and has to be composed of a certain material.

Both criteria coincide.

“When objects in space pull enough gravitational force in their direction, the material that the object is composed of will pull closer to the center, creating a spherical shape,” Taylor said. “Since the gravitational pull is so great, it also causes other nearby objects that orbit the planet, thus making them moons of various sizes.”

Most planets are made up from rock-like materials or gas. Pluto is composed mainly of ice, making it difficult to classify, Taylor said.

Other criteria factor into this as well, Taylor said. Normal planets follow a specific orbit around the sun. The orbit is usually a flat circle similar in shape to a Frisbee, Taylor said.

Pluto’s orbit is circular, but it inclines sending its orbit on a trajectory contradictory to the definition. In fact, Pluto’s orbit actually intersects Neptune’s orbit. No other planet’s orbit interferes with other planets.

The object also needs to be the dominant presence in its part of the solar system. In the case of Pluto, many other small asteroids, moons and dwarf planets share space with it in its part of the galaxy.

The speech concluded with Taylor saying that the astronomical society had decided that Pluto should be classified as a “dwarf planet.” For the time being, that is exactly the way it will be defined. However, theories are constantly changing, and Taylor was confident that the astronomical society could change its mind again.

The speech was supposed to be followed with an observing of Pluto, but due to bad weather that part had to be cancelled.

Taylor is expecting to hold another viewing of the planet sometime in the early part of spring. He encourages students to get involved.

For more information on the event, Taylor can be contacted at [email protected] or at 278-6480.