Since its discovery and classification as the ninth planet in our solar system in 1930, Pluto has been the subject of much controversy in the scientific community.  Its small size and extreme distance from Earth have made gathering specific data about its characteristics difficult, and no real consensus exists amongst astronomers about the information that is known about Pluto.  In 2006, the International Astronomical Union created an official definition for the term "planet" which listed three criteria for classification:

1. The object must be in orbit around the sun.
2. The object must be massive enough to be rounded into a sphere by its own gravity.
3. The object must have "cleared the neighborhood" around its orbit.

Because Pluto is much smaller than the other objects in its orbit, it fails to meet the third condition and has since been known as a "dwarf planet".  Some scientists have gone so far as to suggest that Pluto may actually be one of the many moons of its neighboring planet, Neptune.

When Pluto was first discovered in 1930, astronomers estimated that it may be as large as earth and thus were confident that it was, in fact, a planet.  As our ability to gather information about outer space continues to improve through more powerful telescopes and space probes, scientists are now able to use the new, more accurate information they receive to accurately classify objects in space.  While some still argue that Pluto meets the accepted criteria to be known as a planet, for the time being, conventional scientific thinking will hold that our solar system only has eight planets.

Passage adapted from The Call of the Wild by Jack London (1903)

Again Hal's whip fell upon the dogs. They threw themselves against the breast-bands, dug their feet into the packed snow, got down low to it, and put forth all their strength. The sled held as though it were an anchor. After two efforts, they stood still, panting. The whip was whistling savagely, when once more Mercedes interfered. She dropped on her knees before Buck, with tears in her eyes, and put her arms around his neck.

"You poor, poor dears," she cried sympathetically, "why don't you pull hard?--then you wouldn't be whipped." Buck did not like her, but he was feeling too miserable to resist her, taking it as part of the day's miserable work.

 One of the onlookers, who had been clenching his teeth to suppress hot speech, now spoke up:--

 "It's not that I care a whoop what becomes of you, but for the dogs' sakes I just want to tell you, you can help them a mighty lot by breaking out that sled. The runners are froze fast. Throw your weight against the gee-pole, right and left, and break it out."

 A third time the attempt was made, but this time, following the advice, Hal broke out the runners which had been frozen to the snow. The overloaded and unwieldy sled forged ahead, Buck and his mates struggling frantically under the rain of blows. A hundred yards ahead the path turned and sloped steeply into the main street. It would have required an experienced man to keep the top-heavy sled upright, and Hal was not such a man. As they swung on the turn the sled went over, spilling half its load through the loose lashings. The dogs never stopped. The lightened sled bounded on its side behind them. They were angry because of the ill treatment they had received and the unjust load. Buck was raging. He broke into a run, the team following his lead. Hal cried "Whoa! whoa!" but they gave no heed. He tripped and was pulled off his feet. The capsized sled ground over him, and the dogs dashed on up the street, adding to the gayety of Skaguay as they scattered the remainder of the outfit along its chief thoroughfare.