Mystery Surrounds Thursday's Vote on Pluto's Fate

The 12 planets under the newly proposed IAU definition. Planet sizes are shown to scale but their orbital distances are not to scale. CREDIT: IAU/Martin Kornmesser

A vote that could determine how Pluto is portrayed in future textbooks is set for Thursday at a meeting of the International Astronomical Union in Prague.

Exactly what astronomers will be voting on is not known, however.

At issue is whether Pluto, being smaller than Earth's Moon and traveling an odd trajectory around the solar system, should have ever been termed a planet. Depending on the proposal and the vote, the official tally of planets in the future could range anywhere from eight to hundreds. One possible variation would represent such a radical change that even our Moon could one day be termed a planet.

Three proposals

At least three distinct proposals have been discussed since the IAU revealed it's first draft resolution last week, one that called for the addition of an asteroid and a moon to the pantheon of planets.

Astronomers criticized the original proposal and an alternative was put forth that would strip Pluto of it's planetary status. That idea apparently did not gain enough traction, because a third proposal was then discussed. It melded the other two but was also poorly received, a source told SPACE.com.

Thursday's vote will involve something that springs from the heated debate that's gone on at the meeting since Aug. 16 and which stretches back several years to when some of the first icy worlds were discovered out in Pluto's realm.

4th proposal?

IAU officials will release the refined proposal-which they have sole discretion to modify as they see fit-to the public prior to the vote. It is not known if they'll go with one of the alternate proposals or develop yet a fourth.

"It's been modified from the original proposal," said IAU press officer Helen Sim.

The voting session is to begin at 2 p.m. local time, which is 9 a.m. ET. There are other proposals to be voted on, so it is not known when Pluto's fate will be decided. "The vote will be in first part of the meeting," Sim said in a telephone interview today. "We expect it to all be concluded by 4 p.m. at the latest."

The vote is a "yes" or "no" proposition, so it is possible that the meeting will end with no planet definition.

The session, part of a closing ceremony, is expected to be webcasted here.

The Debate at the IAU Meeting

• Join the Discussion in Robert Roy Britt's Blog
• 3rd Proposal 'Shot Down in Flames'
• Details Emerge on Plan to Demote Pluto
• Pluto May Get Demoted After All
• One Astronomer Says 'It's All About the Atmosphere'
• Earth's Moon Could Become a Planet
• Public Laughs and Shrugs at 12-Planet Proposal
• Astronomers Sharply Divided on New Planet Definition
• Adding Planets Means New Textbooks, Toys
• Nine Planets Become 12 with Controversial New Definition
• Image Gallery: The 12 "Planets"

Defining Moments: The Saga's History

• Pluto's Fate to be Decided by 'Scientific and Simple' Planet Definition
• JUNE: Definition of 'Planet' Expected in September
• 2005: Definition Debate: Planets May Soon Get Adjectives
• 2003: Controversial Proposal Would Boost Solar System's Planet Tally to 12
• 2000: What is a Planet? Debate Forces New Definition