of which are Pluto and Ceres." While this may appear to contradict Stern's objections, Stern noted in an interview with Smithsonian Air and Space that, unlike the IAU's definition, his definition still allows unterplanets to be planets: "I do think from a dynamical standpoint, there are planets that really matter in the architecture of the solar system, and those that don't. They're both planets. Just as you can have wet and dry planets, or life-bearing and non-life-bearing planets, you can have dynamically important planets and dynamically unimportant planets." The density of an object is a rough guide to its composition: the lower the density, the higher the fraction of ices, and the lower the fraction of rock. The denser objects, Vesta and Juno, are composed almost entirely of rock with very little ice, and have a density close to the Moon's, while the less dense, such as Proteus and Enceladus, are composed mainly of ice. References Bibliography and external links What is a planet? -Steven Soter Why Planets will never be defined: Robert Roy Britt on the outcome of the IAU's decision An examination of the redefinition of Pluto from a linguistic perspective. The Pluto Files by Neil deGrasse Tyson The Rise and Fall of America's Favorite Planet Q&A New planets proposal Wednesday, August 16, 2006, 13:36 GMT 14:36 UK David Jewitt's Kuiper Belt page- Pluto Dan Green's webpage: What is a planet? What is a Planet? Debate Forces New Definition The Flap Over Pluto "You Call That a Planet?: How astronomers decide whether a celestial body measures up." David Darling. The Universal Book of Astronomy, from the Andromeda Galaxy to the Zone of Avoidance. 2003. John Wiley & Sons Canada (), p. 394 Collins Dictionary of Astronomy, 2nd ed. 2000. HarperCollins Publishers (), p. 312-4. Catalogue of Planetary Objects. Version 2006.0 O.V. Zakhozhay, V.A. Zakhozhay, Yu.N. Krugly, 2006 The New Proposal, Resolution 5, 6 and 7 2006-08-22 IAU 2006 General Assembly: video-records of the discussion and of the final vote on the Planet definition. Boyle, Alan, The Case for Pluto'' The Case for Pluto Book by MSNBC Science Editor and author of "Cosmic Log" Croswell, Dr. Ken "Pluto Question" Pluto Question Planetary science Planets of the Solar System Planets History of astronomy Planet Astronomical controversies