Pluto’s Demise Remains Controversial
By Dr. Syed Amir
Bethesda, MD

In late February on a starry night in 1930, a young student, Clyde Tombaugh, barely 24-years old, was peering down a telescope at the Lowell Observatory located at Flagstaff in the Arizona desert when he made some remarkable observations that led to the discovery of Pluto. Yet, ever since its discovery almost 76 years ago, the status of Pluto as the ninth planet has remained a subject of relentless controversy, one that has only been exacerbated by time.
This long-standing controversy aside, Pluto’s discovery makes a fascinating story. Growing up on an agricultural farm, Tombaugh had inherited a passion for astronomy and a zeal for stargazing from his father, and as a boy had constructed his own rudimentary telescope to observe Jupiter and Mars. His ambition was to study astronomy at a university, but his family did not have enough money to support his quest for higher education. He therefore started to look for alternative opportunities to fulfill his aspirations.
Tombaugh got his opportunity when he went to work at the Lowell Observatory. The celebrated American astronomer, Percival Lowell, who founded the Lowell Observatory in 1894, had been intrigued during his life time by his finding that the orbits of two known planets, Uranus and Neptune, seemed to deviate from their predicted course. He theorized that the observed perturbations were caused by the gravitational pull of another planet yet to be discovered. He named this unknown planet, X. Following his death in 1916 other astronomers continued to look for the presence of the hypothetical planet in the sky. It was not an easy undertaking and the planet X defied for many years all attempts to find it.
When Tombaugh was interviewed for a job at the Lowell observatory, the scientists who interviewed him were impressed by his youthful enthusiasm and promptly offered him a position. He was assigned the task of surveying the heavens for the elusive planet, photographing the constellations on different nights and then meticulously studying the photographic plates for any evidence of the unknown planet.
In their search, the astronomers were hoping to take advantage of the differences in the relative movements of stars and planets. Stars move little relative to each other over a short time, but planets orbit the sun, shifting their positions significantly relative to stars in the night sky. The two planets located at the edge of our solar system, Uranus and Neptune, are so far away from us that they are visible only as spots of light in the darkness. The only hope the young astronomer had for finding the new planet in the neighborhood of Uranus and Neptune was to be able to identify a speck of light in the distant sky that shifted its position, as opposed to numerous others that did not move at all.
After persevering for a year and help with serendipity, Tombaugh was finally able to locate the planet X by comparing its image with thousands of stars all of which he had captured on his photographic plates. Paradoxically, while the new planet was found in the region where the astronomer Lowell had predicted that it would be, the initial prediction itself was based on an incorrect premise. Later calculations showed that there was no true deviation in the orbits of Uranus and Neptune, as Lowell had long believed; he had merely made an error in his orbital calculations. The new planet was named Pluto, after the Greek god of the underworld, following the suggestion made by an eleven-year girl from Oxford, England, who was interested in classical mythology. The exotic name was nicely consistent with Pluto’s cold, frozen character and its remote location. It was the only planet ever discovered by an American.
With the addition of Pluto, the number of planets in the solar system went up from eight to nine. But even as school textbooks and astronomical documents were getting updated, and children were struggling to learn the names of the nine planets, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and now Pluto, the status of Pluto as a planet was steadily coming under attack. Initially believed to be of much larger size, larger than mercury, Pluto turned out to be of much smaller size, as more powerful and sophisticated instruments became available to study it. The original calculations of Pluto’s size were erroneous, because the telescopes available at the time could not separate Pluto from its large satellite, Chiron, giving the illusion of a larger body. In fact, Pluto has a diameter of only 1,440 miles, or less than one-fifth the size of our earth. Its distance from the earth is estimated to be 2.67 billion miles, and it is so far away from the sun, 3.7 billion miles, that when viewed from its surface the sun looks like a dim star.
As the full realization of Pluto’s true size and density emerged, it re-ignited the controversy as to why it should continue to be classified as a planet and not considered a comet. Comets are small celestial bodies that are made mostly of ice and stellar debris and abound in the outer regions of the solar system. Pluto, based on available information, is believed to have an icy surface that consists of 98% nitrogen, mixed with small amounts of methane and carbon monoxide. Its small size has also been problematical, since a number of moons that orbit planets are known to be larger than Pluto.
To settle the question of whether Pluto is a planet or a comet, the International Astronomical Union (IAU) appointed a committee to make a final recommendation about its status. The seven-member committee met in June and July this year, and returned with a recommendation designed to please everybody. They proposed the creation of a new subcategory of small planets to be called Plutons. They further recommended that Pluto be placed in this special category to distinguish it from the eight established planets. However, the new proposal failed to carry a majority support of the astronomers and astrophysicists. At its meeting in Prague where 2,500 astronomers gathered on August 24, 2006, IAU, after much acrimonious debate, decided to strip Pluto of its status as a planet. They settled on a new definition of planets, according to which a planet must have an orbit that is clear of all debris and smaller celestial bodies. Pluto did not qualify, as it travels mostly through a ring of icy chucks and debris, the so-called Kuiper belt, and its orbit is crossed by the much larger planet, Neptune.
The decision of IAU, however, has not settled the controversy -- far from it. Recently, more than 300 planetary scientists and astronomers in the United States signed a petition protesting the IAU’s decision and expressing their disagreement with the new definition of a planet. They are planning to have their own international conference next year and propose to reopen the debate. Thus, the final chapter on the status of Pluto may not yet have been written.
Meanwhile, Pluto’s demotion to the status of a dwarf planet not only dismayed school children around the world who seem to have special affection for it, it also saddened the widow of Tombaugh, the discoverer of Pluto who died in 1997 at age 90. Tombaugh’s ashes are currently being carried by the spacecraft, New Horizons, which will rendezvous with Pluto in the year 2015 and will scatter his remains on the former planet’s surface. Alas, Mrs. Tombaugh who is 93 years old is unlikely to be alive to celebrate the event.

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