OUR FAR-FLUNG CORRESPONDENTS about astronomer Mike Brown and the discovery of a tenth planet. There are 9 planets in our solar system. Or 8, or 10, or maybe even 23. A planet is an arbitrary thing. In a matter of weeks, however, the International Astronomical Union (I.A.U.) is likely to issue a definitive description. For many years, the planets have been the 9 largest objects in orbit around the sun. The case for the 9 regards Pluto-discovered in 1930 by Clyde Tombaugh-as the 9th planet. The case for 8 eliminates Pluto, claiming it's more of a transneptunian object. The transneptunian region is called the Kuiper Belt. The case for 10 planets accepts Pluto and considers the largest Kuiper object, currently called 2003 UB313 (or Xena), as the 10th planet, since it's larger than Pluto. The argument for 23 planets regards a planet as any big, round object in our solar system. 2003 UB313 was discovered on January 5, 2005, by an astronomer named Mike Brown, a professor at Caltech. It's the largest object discovered in the solar system since Neptune's moon Triton, in 1846. Brown has already found the 7 largest objects in the solar system that aren't currently thought of as planets-he has also found the 9th largest-all of which reside in the Kuiper Belt. If the I.A.U.'s definition allows 23 planets, Brown will have found 8 of them, more than anyone else ever has. Brown began teaching at Caltech in 1997. Describes his search of the skies at the Palomar Observatory, which began in July, 1998. Using a new kind of digital camera, Brown was able to track objects to see if they were moving or not. In 2000, he bet a friend that he would find a new planet before December 31, 2004. Describes how the computer selects possible planetary objects from thousands of photographs. Brown was born in 1965, in Alabama. He studied physics at Princeton and then focused on graduate work in astronomy at Berkeley. At Palomar, with the digital camera, Brown and his team, including Chad Trujillo and David Rabinowitz, began finding big things. In June, 2002, they found an object half the size of Pluto; describes how they named it Quaoar, from Tongva Indian mythology. In November of 2003, Brown discovered another object, bigger than Quaoar; they named it Sedna, from Inuit mythology. Two weeks before Brown's bet expired, he found another object that he named Santa. On January 2, 2005, Brown was looking through archival digital images when he found a bright object farther out and bigger than Pluto. After using the Hubble Telescope in December of 2005, he was able to determine that the planet was a little larger than Pluto. Having discovered Xena, Brown began studying it in order to describe it in a paper. Brown hadn't told anyone about his findings except his wife and the members of his team. In July, a conference of astronomers published on the Internet an abstract of Brown's presentation to the conference on Santa. A week later, a team of astronomers in Spain announced that they'd found the brightest object in the Kuiper Belt; it was Santa. Brown's heart sank, but he congratulated the Spanish team. Mentions Brian Marsden, the director of the Minor Planet Center. On July 29th, Brown typed into Google Santa's technical name, and it came up with a Web page in Ohio. The web page was a record of where Brown had aimed the telescope; any astronomer could find what Brown had been looking at. From Marsden, Brown heard that an astronomer in Germany had found other objects Brown had discovered on the Ohio Web site and had calculated their orbits. On August 9th, Brown wrote to the Spaniards who had looked at records of his work, calling what they'd done an “ethical breach.” Brown was uncertain whether to call Xena a planet or not. “When I used to argue for 8, I felt as if there was a public sentiment that you couldn't get rid of Pluto…” The writer describes looking at images of the deep sky with Brown.