Dwarf planet to gradually become tidally locked, such that it always presents the same face to its companion. An extreme example of this is the Pluto–Charon system, where both bodies are tidally locked to each other. Earth's Moon is also tidally locked, as are many satellites of the gas giants. The upper and lower size and mass limits of dwarf planets have not been specified by the IAU. There is no defined upper limit, and an object larger or more massive than Mercury that has not "cleared the neighbourhood around its orbit" would be classified as a dwarf planet. The lower limit
The Pluto Files The Pluto Files The Pluto Files: The Rise and Fall of America's Favorite Planet is a book written by the astrophysicist and Hayden Planetarium director Neil deGrasse Tyson. The book is about Pluto, which was demoted to the status of dwarf planet in August 2006 by the International Astronomical Union, thereby depriving it of its planet-hood. The book also focuses on the fact that many Americans rallied their support for this icy dwarf on the edge of the Solar System because it was discovered by an American. The book was given a good review by Jon Stewart in a guest