PLUTO (ONCE AND FUTURE PLANET?): In 2006 an international group of astronomers demoted the ninth planet, Pluto (shown here with its moon Charon), to a lowly dwarf planet. The bitter debate over the change is set to continue later this summer.
NASA

Pluto lovers, don't despair: Researchers have not given up the fight for the former ninth planet. Many of them put up a fuss two years ago when the International Astronomical Union (IAU) downgraded Pluto to the status of mere dwarf planet. Now they plan to revive the debate, this time under the banner of public understanding of science.

Researchers on both sides of the issue are set to gather in August at Johns Hopkins University Applied Physics Laboratory in Laurel, Md., for what's being called "The Great Planet Debate: Science as Process." The goal, says the conference's co-organizer Mark Sykes, director of the Planetary Science Institute in Tucson, Ariz., is to teach the public that science is a process of constant revision and refinement. "People should be exposed to that process," he says. "The IAU process gave the impression that science is done by a bunch of scientists voting behind closed doors."

The schedule for the upcoming conference includes back-to-back talks on the current IAU definition of a planet (a round body that has cleared its orbit of competitors) as well as an earlier version, preferred by researchers such as Sykes. Also listed is a talk on "challenges and opportunities" for teachers, who are invited to attend. "One of the problems over the last couple of years," Sykes says, "has been [that] teachers have been confused what to teach"

The lingering resistance to the IAU's decision irks some researchers. "I think fighting it is doing more damage to our reputation than anything," says Harold Levison, a planetary scientist at the Southwest Research Institute in Boulder, Colo. He agrees with the IAU's conclusion, he says, but adds that he would have rather seen planets divided into two groups: major and minor. The IAU could still decide to revisit the subject in a meeting scheduled for next year.

Despite the rift, textbook publishers seem to be taking Pluto's demotion in stride. Some contacted by ScientificAmerican.com say they anticipated it. An early draft of Perspectives on Astronomy (first edition, 2007), written before the August 2006 IAU meeting, excluded Pluto from a map of the planets in the solar system, says text co-author Dana Backman, a planetary scientist at NASA Ames Research Center, Moffett Field, Calif.

"The IAU decision was expressing what we already believed, and had put words to paper about," Backman says. He provided an excerpt of the published first chapter by e-mail, which briefly recounted Pluto's demotion but did not describe it as controversial.

Planetary Sciences (first edition, 2001) counted Pluto among the planets but will exclude it in the second edition, due out in 2009, according to Backman's fellow Ames researcher Jack Lissauer, co-author of the text, who shared the 2007 Chambliss Astronomical Writing Award from the American Astronomical Society with co-author Imke De Pater.

Pluto has always stood out from the other planets. At roughly a fifth the mass of the moon, it is the largest of the icy bodies that make up the Kuiper belt beyond Neptune's orbit. Unlike the four inner (terrestrial) planets, it has a tenuous atmosphere at best.

The outer four Jovian planets are massive and gaseous. None resemble the former ninth planet, which also has a distinctly eccentric, or elliptical, orbit that crosses that of Neptune. "When you look at a plot like that [of eccentricity], there's eight planets," Levison says. "It just jumps out and bites you in the butt."