Star Points for September, 2006; by Curtis Roelle Understanding the IAU's Pluto Decision Everyone who began attending school after Pluto's discovery on February 18, 1930 learned our solar system has nine planets. This changed last month when the International Astronomical Union (IAU) issued a decree shrinking that count to eight by downgrading Pluto to the paltry status of "dwarf planet." In a nutshell the decision was based on a newly drawn definition of planet. According to the Smithsonian Institution's National Air & Space Museum (NASM) web site, the IAU rule says that a planet must meet the following criteria: A planet 1) is a celestial body that orbits the Sun; 2) is massive enough that its own gravity causes it to form in a spherical shape; and 3) has cleared the neighborhood around its orbit. Where Pluto fails in the third rule. It is in an area of the solar system called the "Kuiper Belt." It is an outer asteroid belt. By the way, the main asteroid belt between Mars and Jupiter contains the asteroid Ceres which has been promoted to dwarf planet status, joining Pluto. There are currently two other dwarf planets in our solar system -- both farther away than Pluto. Other criteria could have been used. For example maybe a planet has to have moons. Pluto has four. But this would have knocked out Mercury and Venus which have none. Just who does the IAU think they are that they can take away an entire planet? The organization was founded in 1919. According to their web site the IAU's "mission is to promote and safeguard the science of astronomy in all its aspects through international cooperation." With members in 85 countries the IAU is the internationally recognized authority for standard astronomical policies and naming conventions. For example, it was the IAU that designated the names and drew the borders for the 88 constellations in 1930. The IAU is also charged with issuing names for newly discovered objects such as planetary moons, asteroids, and dwarf planets. An IAU committee was tasked with drawing up a testable scientific definition of what a planet is. That definition that leaves Pluto where it was found -- out in the cold. From the time of Clyde Tombaugh's 1930 discovery of the ninth planet until its demotion Pluto has only traveled 30% of its 248 year long circuit around the sun. When found Pluto was in the constellation Gemini. It moved into Cancer and spent the mid- 1950's in Leo's head. After that it has visited Virgo, Libra, Serpens Caput (serpent's tail), Ophiuchus, Scorpius, and Serpens Cauda (serpent's head). Pluto reaches Sagittarius in December. By the way, Scorpius is the proper name, not "Scorpio." Also there's no such thing as "Capricorn" -- it's called Capricornus. If you don't like it then you can take it up with the IAU. The Westminster Astronomical Society Inc. (WASI) had a tent at the State Fair. Each day hundreds of passersby paused to safely view the sun through a telescope or to take a look at the scale model public observatory the group is raising money to build just outside of town near Westminster. Many who stopped by expressed their feelings about the IAU Pluto decision. The views expressed ranged from resigned disappointment to border outrage. Although the IAU is within its bounds to treat Pluto any way it wishes, there is a backlash emerging. On its web site Sky & Telescope magazine reports that "a small but growing group of scientists made their first formal attack against the International Astronomical Union's August 24th resolution." The astronomers most radical action so far was to ciruclate a petition. Among them is Alan Stern who leads the ongoing New Horizons spacecraft mission to Pluto. New Horizons is scheduled to reach Pluto in 2015. It was launched earlier this year on a mission to encounter the only major planet that has not been visited by a spacecraft from earth. With the IAU's decision suddenly no planets remain unvisited. The last one, Neptune, was encountered by Voyager II way back in 1989. For now the dust hasn't quite settled on the Pluto issue. Will the petitions meet with success and overturn the IAU? Only time will tell. In the meantime Pluto itself remains unchanged.