• PROJECTS
• THE PLANETARY REPORT
• PLANETARY RADIO
• WEBLOG
  • Archive
  • Future Space Events of Note
  • Special Coverage
  • Video Archives
• SOCIETY UPDATES

browse projects: Apophis Mission Design Competition Asteroid Impact Mapping System Catalog of Exoplanets Drive a Mars Rover Extrasolar Planets Transit Search International Lunar Decade LIFE Experiment: Phobos Mars Climate Sounder Team Website Messages from Earth Observing Earth Pioneer Anomaly Planetary Microphones S.O.S: Save Our Science! SETI Optical Telescope SETI Radio Searches SETI@home Shoemaker NEO Grants Solar Sailing Space Advocacy Space Information Stardust@home Target Earth Visions of Mars

browse space topics: 2001 Mars Odyssey Asteroids and Comets Cassini-Huygens Chandra X-Ray Observatory Chandrayaan-1 Chang'e 1 Compare the Planets Dawn Deep Impact Earth Extrasolar Planets Genesis Hayabusa (MUSES-C) Hubble Space Telescope Jupiter Kaguya (SELENE) Lunar Reconnaissance Orbiter (LRO) Mars Mars Exploration Rovers Mars Express Mars Global Surveyor Mars Reconnaissance Orbiter Mars Science Laboratory Mercury MESSENGER Moon Near Earth Objects Neptune New Horizons New Horizons Digital Time Capsule Past Missions Phoenix Planetary Analogs Planetary Exploration Timelines Planetfest 2008 Pluto and Charon Pluto Top Ten Postcards from Venus Private Missions Rosetta Saturn Search for Extraterrestrial Intelligence SMART-1 SOHO Space Imaging Spitzer Space Telescope Stardust Trans-Neptunian Objects Ulysses Uranus Venus Venus Express Voyager Weekly Planetary Radio Trivia Contest

The Planetary Society Weblog

By Emily Lakdawalla

Tenth Planet update

Weblog Archive

Astronomer Mike Brown has posted some new information on his website about the status of the 10th planet. There are two key updates. First, it turns out that the Spitzer observations they attempted of 2003UB313 were incorrectly pointed. The failure to detect the 10th planet using Spitzer is what had set their upper size limit. So that means that 2003UB313 is still known to be bigger than Pluto, but they no longer know the upper size limit. Still, based on its spectral similarity to Pluto, they're predicting a size of roughly 125% the size of Pluto. They will attempt Spitzer observations again at the end of the month.

The other update has to do with the naming of the body. Brown reports that there is wrangling among at least three different committees of the IAU. One committee is attempting to develop a definition for the word "planet;" another committee, the one in charge of naming asteroids and Kuiper Belt Objects is considering the name that Brown's team proposed for 2003UB313; and a third committee, the one that approves names for features on major planets and satellites, has asserted that if 2003UB313 is deemed a "planet," then the naming falls to them and must follow the Greco-Roman tradition.