8/30/2006

Pluto and the three dwarfs
(Disney move over)
By Tom Range, Sr.

First it was Earth revolves around the Sun.  Then it was Earth is not flat.  Then it was the Moon is not made of green cheese.  Now, Pluto is not a planet.  It is so confusing!

On August 24, 2006, the International Astronomical Union decided to re-categorize Pluto as a "dwarf planet."  The spatial body that on March 13, 1930, was declared as the ninth planet in the solar system is now considered little more than the ninth rock from the Sun.  The object formerly known as planet Pluto was discovered by astronomer Clyde Tombaugh working at Lowell Observatory in Flagstaff, AZ, and originally was referred to as "Planet X."  Planets are traditionally named for characters in Greek and Roman mythology.  So Planet X became Pluto, the named suggested by Venetia Burney, an 11-year-old schoolgirl in Oxford, England.  Pluto, the god of the underworld, rules in the bleak darkness of an orbit that takes 248 Earth years to complete.

Upon the development of advanced astronomical instrumentation and space exploration, it turned out Pluto is smaller than the Moon and has a mass just two tenths of one percent of Earth.  What is more, Pluto's orbit around the Sun is tilted compared to the other planets.  Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune line up within a degree or two of a flat plane through the Sun.  Their orbits are nearly circular.  Pluto's path is tilted 17 degrees to that plane and is so elliptical that for the 20 years from 1979 to 1999 Pluto had actually been the eighth planet of the Solar System, closer to the Sun than Neptune.  Some astronomers began taking a skeptical view of little Pluto, wondering if what Clyde Tombaugh discovered was really a large comet instead of a small planet.

Then there is the matter of Pluto's moon, Charon, discovered by astronomers at the U.S. Naval Observatory in Flagstaff.  Charon is about half the size of Pluto itself and named, appropriately, after the mythological character who ferried the dead across the river Styx and into the underworld of Pluto.  Pluto and Charon are almost a double planet system.  They dance around each other all the while showing exactly the same faces.  Charon hangs motionless in the Pluto sky, and vice-versa.  NASA has long had plans for a mission to Pluto.  The original concept was the Pluto-Kuiper Express, which was later changed to New Horizons.  That mission was successfully launched on January 19, 2006 and is on its way to Pluto right now.  The Pluto mission hopes to map the planet and its moon, and also the Kuiper Belt, a region of minor icy planets that orbit the sun in almost complete darkness.

It was hardly the first time that astronomers have rethought a planet.  The asteroid Ceres was hailed as the eighth planet floating in the space between Mars and Jupiter when astronomer Giovanni Piazza first discovered it in 1801.  It remained a "planet" for about half a century until the discovery of more and more objects like it in the same part of space led astronomers to dub them asteroids and their collective orbits the Asteroid Belt.

Joining the object formerly known as Planet Pluto in the demeaning status of dwarf planet are its own satellite Charon, Xena (officially designated VB313) that is larger than Pluto and like it orbits out beyond Neptune in the zone of ice debris known as the Kuiper Belt, and the aforementioned Ceres, the largest asteroid in the Asteroid Belt between the orbits of Mars and Jupiter.  Whatever its status, Pluto will continue to travel an orbit that brings it from 2.7 billion to 4.7 billion miles from Earth, and one of its years will continue to equal 248 Earth years.

It surely was not coincidence that Walt Disney named one of his animated figures Pluto.  A caricature of a bloodhound, the character that eventually evolved into Pluto made his debut unnamed in a 1930 cartoon "The Chain Gang."  In May 1931, after a second cartoon in which the character was named "Rover," Pluto was finally given his own name and appeared in the cartoon "The Moose Hunt" as Mickey Mouse's pet.  The Walt Disney organization has so far not announced demoting Pluto to puppy status.

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