An international group of astronomers trying to define the term planet may be finally nearing a decision, but a consensus is unlikely.
If a decision is soon rendered as expected, with or without consensus, the result will be less of a definition, however, and more a string of qualifying adjectives.
Pluto and 2003 UB313 could be called Trans-Neptunian objects. Earth would be called either a terrestrial planet or perhaps a "cisjovian" planet, meaning it's inside Jupiter.
Further complicating the matter are extrasolar planets much more massive then Jupiter, planet-like objects orbiting dead stars called pulsars, and possibly even free-floating worlds that don't orbit stars.
If that's to be the case, then the group's chairman, Iwan Williams of Queen Mary, University of London, will likely have to act without consensus.
"Every time we think some of us are reaching a consensus, then somebody says something to show very clearly that we're not," said Brian Marsden, a member of the group and leader of the Minor Planet Center where newfound objects are catalogued.
Today Marsden told SPACE.com that it's not clear if a consensus will be reached soon. "I thought maybe we were close," he said, "but just yesterday somebody [in the group] insisted we define planet."
That's the very effort that's gone mostly in circles for many months, however.
Nonetheless, a subcommittee within the working group was formed and is supposed to report back Friday. Marsden calls the effort "not helpful" because "it's quite clear we weren't going to agree on a meaning for the word planet."
"I don't believe we should classify planetary objects by location," committee member Alan Stern of the Southwest Research Institute told Nature. "We should use properties of the objects as a guide."
Group member Alan Boss said there is a majority that agrees with the adjective plan and "a minority that's still upset."
Boss, a planet-formation theorist at the Carnegie Institution of Washington, sees the whole affair as a positive one for science. "We know so much more now" about the types of objects that are out there, Boss said in a telephone interview today, that even though a consensus is unlikely, the act of expanding the classification system is a healthy one.
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