2006-10-13 / Columnists

Drawing On Science

Pluto Demoted
Commentary by Stephen Yaeger

In the 1930's, astronomer C.W. Tombaugh snapped thousands of photographs through the lens of the Lowell Observatory's telescope in Flagstaff, Arizona. He was searching for the object that Percival Lowell believed was the reason for the divergences in the predicted and observed motions of the planets Neptune and Uranus.

The observatory was founded by Perceval Lowell who made many unsuccessful calculations as to where the object would be, so he funded two searches for his "Planet X". It wasn't until the observatory's director, Vesto Slipher, hired Clyde Tombaugh for a third search that success was finally achieved. Tombaugh calculated that somewhere near the orbits of Neptune and Uranus there must be an unknown celestial object responsible for the divergence in the planets' orbits.

Tombaugh's photographs were taken one to two weeks apart.

He looked for anything that appeared to shift against the backdrop of the stars.

He carefully studied the many photographs and on February 18, 1930 the 24 year old Tombaugh was able to identify a small object which appeared to change location among the stars.

He had what he was looking for. But Tombaugh's object was too small to be Lowell's "Planet X".

The public suggested many names for the newly discovered planet including Artemis, Vulcan, Cronus and Atlas. Lowell's widow (he died in 1916) suggested Zeus for the planet's name, but later changed it to Constance. It was also suggested that the planet be called Lowell in honor of the astronomer.

Finally it was officially called Pluto, a name originally suggested by 11-year old schoolgirl, Venetia Burney of Oxford, England.

Pluto was aptly named as it is in perpetual darkness and it is the name of the Roman god of the underworld, Erebus (Greek: Hades). Thus it became the fifth member of the Jovian Planets, which includes Saturn, Jupiter, Uranus and Neptune. The Terrestrial Planets are Mercury, Venus, Earth and Mars.

As a member of the solar system, Pluto is the farthest body from the sun and orbits it every 249 years, but its eccentric orbit brings it closer to the sun than Neptune for a period of 20 years. Its size is about the size of our moon.

It has crossed Neptune's path many times in the history of the solar system...the last time in 1999. Pluto will not cross Neptune's path again until 2226. It rotates on its axis every 6,387 days, which is the same as its satellite, Charon making it the only body in the solar system which is synchronized with its satellite.

In November, 2005 two more satellites of Pluto were discovered.

On August 24, 2006 the International Astronomical Union agreed on a definition of a Major Planet which is described as a celestial body that is in orbit around the sun, has sufficient mass for its self-gravity to overcome rigid body forces, has a nearly round shape, and has cleared the neighborhood around its orbit.

The IAU defined a Dwarf Planet among other things as being in orbit around the sun, has sufficient mass for its self-gravity to overcome rigid body forces, has a nearly round shape, has not cleared the neighborhood around its orbit and is not a satellite. Small Solar System Bodies include asteroids, comets and natural satellites.

Unfortunately Pluto does not meet the criteria of a major planet since it appears to orbit Neptune and has been redefined as a dwarf planet...something attempted in 1999, but protests derailed the classification...with the IAU number 134340.

In 2005 Michael Brown of CIT in Pasadena discovered a small celestial body and named it "Xena" (after the TV adventure character) with the number 2003 UB313, but with the controversy surrounding Pluto's designation Xena's name was changed to Eris after the Greek goddess of discord and strife.

Questions/comments/suggestions? E-mail Steve: Drawingonscience@aol.com

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