Resurrecting Pluto

As Sciencebase reported recently, a session of the International Astronomical Union (IAU), meeting in Prague, during August passed a resolution re-defining the nature of the planets of our solar system. Apparently, only about 428 of the IAU’s almost 10000 membership was involved in the voting. The original proposal would have led to an expansion of our solar system from the familiar nine planets to 12, for now. But, as we now know things turned out very differently.

This proposal was modified at the conference, with the aim being to exclude from the definition of planet all but the eight largest planets, which meant Pluton was dwarved. The vote leaned towards this definition, much to the chagrin of the wider IAU community, which believes neither definition was subject to critical review by the broader planetary
science community prior to the conference, despite simple means to do so.

A grass roots petition 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” has now emerged –

According to a press release from the Planetary Science Institute, in less than five days more than 300
professional planetary scientists and astronomers had signed the petition. “The list of signatories includes researchers who have studied every kind of planet in the solar system, as well as asteroids, comets, the Kuiper Belt, and planet interactions with space environment. They have been involved in the robotic exploration of the solar system from some of the earliest missions to Cassini/Huygens, the missions to Mars, ongoing missions to the innermost and outermost reaches of our solar system, and are leading missions preparing to be launched,” says the release.

The list also includes prominent experts in the field of planet formation and evolution, planetary atmospheres,
planetary surfaces and interiors, and includes international prize-winning researchers.

“This petition gives substantial weight to 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, Arizona. “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.”

So, as we predicted, Pluto’s status could be changed yet again. Meanwhile the guy on the Clapham omnibus will probably stick with the idea that Pluto is a planet regardless of the outcome of this debate.


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