Pluto a planet? Not a planet? Beloved Disney Dog?
The Pluto Controversy
Pluto the dog lives on as an animated character, but as far as being the ninth planet of our Solar System, Pluto has passed on by definition.
In 2006 the International Astronomical Union, the currently recognized collection of astronomical “deciders,” stated that, in the Solar System, a planet is a celestial body which:
1. is in orbit around the Sun,
2. has sufficient mass to be nearly round in shape, and
3. has “cleared the neighborhood” around its orbit.
A body fulfilling only the first two of these criteria is classified as a “dwarf planet,” so Pluto was demoted to that lowly status for not clearing its neighborhood.
The controversy evolved from the fact that scientific advances have led to the discovery of dozens of objects, at least one more massive than Pluto, that previously could have been called “planets.”
Pluto lives in the Kuiper Belt, a region of the Solar System beyond the orbit of Neptune, approximately 3 to 5 billion miles from the Sun. The belt was discovered in 1992. Since then, the number of known Kuiper belt objects has increased to over a thousand, and more than 100,000 objects wider than 62 miles are believed to exist.
Who could have imagined that in the 1930s when Pluto became the 9th planet?
In addition, Pluto, once thought to be more massive than Earth, is now known to be about 1/459th of Earth’s mass.
Some find it sad that Pluto cannot be a “real” planet anymore, but the line has to be drawn somewhere, doesn’t it?
You’ve been listening to “Western Slope Skies,” produced by members of the Black Canyon Astronomical Society. I’m Joyce Tanihara.