This book is revised to expand on the Pluto Controversy. To give young readers the science behind the headlines, astronomer Ken Croswell has revised the acclaimed "Ten Worlds" - the most substantial and beautiful children's book about the solar system. Pluto is demoted and astronomers revolt! In 2006, hundreds of astronomers voted that icy Pluto was not a planet. But hundreds of other astronomers signed a petition refusing to recognize that vote. Is Pluto just an oversized comet - too small to be a planet? Or does it deserve the status it has had for seventy-six years? Tenth Planet is discovered! "Ten Worlds" is the only children's book with the full story of the tenth world, Eris. Its discovery in 2005 rekindled the old dispute about Pluto and triggered the controversial vote. Eris is bigger than Pluto. If Pluto is a planet, isn't Eris one, too? Croswell informs readers about the discovery of Eris and the long-running argument about what makes a planet. Also in "Ten Worlds", you find: large, lavish photographs, the latest on each of the planets and the seven biggest moons in the solar system.