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Pluto gone? Not so fast!

In the wake of Pluto's demotion from the roll of solar system planets, astronomers are pointing out that a lot of the nitty-gritty details still need to be worked out - and that the plucky erstwhile planet shouldn't be counted out quite yet. Just wait until 2009!

Here's today's statement from the American Astronomical Society's Division of Planetary Sciences:

"Some questions have arisen over the recent International Astronomical Union (IAU) resolutions that defined three categories of bodies in the solar system: planets, dwarf planets, and small solar system bodies. These concerns are not surprising, given the long and difficult history of efforts to reach agreement on just what a planet is, and the unwillingness of nature to be categorized into neat compartments.

"The Division for Planetary Sciences (DPS) of the American Astronomical Society (AAS) recognizes the authority of the IAU to render a decision, and notes that it had considerable input by DPS members in the process.

"However, it is also mindful of the fact that future refinements of this definition will almost certainly be desired. All definitions have a degree of fuzziness that requires intelligent application: what does 'round' really mean? What does it mean to 'control a zone'? These are technical issues to be addressed by Division III of the IAU, currently chaired by Ted Bowell, a fellow DPS member. There is still work to be done, too, in constructing a definition that is generally applicable to extrasolar planetary systems. These and other changes, radical or moderate, presumably will be addressed at the next IAU General Assembly in Rio de Janeiro in 2009, and the DPS community will continue to be involved in all stages of this process.

"Ultimately, the definition of a planet will come through common usage and scientific utility. There is no need to throw away current school texts; Pluto has not gone away.  We will continue to explore Pluto and the other objects orbiting beyond Neptune with telescopic observations and spacecraft missions to obtain a fundamental understanding of their place in our solar system.

"The DPS is the largest international professional organization of planetary scientists with approximately 1,300 members of which about 30 percent are from non-US countries."

While you're waiting for the final answer, take a walk on the lighter side of Pluto: Check out this cartoon roundup and Jason Kottke's list of new planetary memory aids.

Update for 10:10 p.m. ET: Hoo boy, the Pluto protest movement is growing. Space.com's Robert Roy Britt rounds up the resistance in this article and this blog posting. Late today, a fresh wave of criticism came to light from the Center for Space Exploration Policy Research and the Planetary Science Institute. Here's their news release:

"On August 24, a session of the International Astronomical Union (IAU) General Assembly in Prague passed a resolution re-defining the planets of our solar system. Only 428 of the IAU’s nearly 10,000 members were involved in the vote. A proposal crafted over the previous year by the IAU Planet Definition Committee would have expanded the number of objects designated as planets in the solar system to 12, with the potential for additions in the future. At the assembly, however, the proposal was modified over the course of several days to define the term with the intent of excluding all but the eight largest planets.

"Neither definition was subjected to critical review by the broader planetary science community prior to the assembly.

"As part of its role to examine the nature of scientific authority, the Center for Space Exploration Policy Research (CSEPR) is considering the role of the IAU and its findings, as well as a petition to reevaluate the principles for planet definition.

"Just after the August 24 vote, members of the space science community pointed out serious technical and pedagogical flaws in the IAU’s definition of planets. As a consequence, a grass-roots petition was posted, stating:

"'We, as planetary scientists and astronomers, do not agree with the IAU’s definition of a planet, nor will we use it. A better definition is needed.'

"The statement was placed on the Web at http://www.ipetitions.com/petition/planetprotest and circulated by e-mail to a small fraction of the world’s astronomical research community.

"In less than five days, the petition was signed by 300 professional planetary scientists and astronomers. The list of signatories (posted at the Web site above) includes researchers who have studied every kind of planet in the solar system, as well as asteroids, comets, the Kuiper Belt and planetary interactions with the space environment. Many have been involved in the robotic exploration of the solar system from some of the earliest missions to Cassini-Huygens, missions to Mars, and ongoing missions to the innermost and outermost reaches of our solar system.

"Others are leading missions that are preparing for launch. The petition list includes prominent experts in the field of planet formation and evolution, planetary atmospheres, planetary surfaces and interiors, as well as international prize-winning researchers.

"'This petition gives substantial weight to the argument that the IAU definition of planet does not meet fundamental scientific standards and should be set aside,' states petition organizer Dr. Mark Sykes, director of the Planetary Science Institute in Tucson, Ariz. 'A more open process, involving a broader cross section of the community engaged in planetary studies of our own solar system and others, should be undertaken.'

"'I believe more planetary experts signed the petition than were involved in the vote on the IAU’s petition,' adds co-sponsor Dr. Alan Stern, executive director of the Space Science and Engineering Division at Southwest Research Institute. 'From the number of signatories that the petition received in a few days, it’s clear that there is significant unhappiness among scientists with the IAU’s planet definition, and that it will not be universally adopted by scientists and textbook writers.'

"'A key public policy question is who has the social mandate to alter the definition of something as fundamental as a planet,' says Dr. Mark Bullock, director of the CSEPR. 'Scientists have in the past vested the IAU with authority to name asteroids and other planetary objects. However, the word "planet" has cultural, historical, and social meaning and as such requires much broader discussion and consensus than those required for the naming of astronomical bodies.'

"The CSEPR is currently examining the nature of scientific authority, and its use and misuse in issues of fundamental concern to the public. The scientific and cultural value of the definition of planets, both within and outside our solar system, is of utmost significance. Accordingly, continues Stern, 'To achieve a good planet definition that achieves scientific consensus will require more work.'"

It should be noted that Stern is the principal scientific investigator for NASA's New Horizons mission, which was launched toward Pluto earlier this year. Sykes is a co-investigator for NASA's occasionally endangered Dawn mission - which will target another "dwarf planet," the asteroid Ceres. Bullock's specialty is planetary atmospheres, particularly on Venus and Mars.

So is this a time to "teach the controversy"?