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Pluto politics left behind

Dancers perform during opening ceremonies for the International Astronomical

Union's General Assembly in Rio de Janeiro Tuesday. Pictures of Pluto and other

dwarf planets are displayed on the screen above the stage, in the most visible

reference to the controversy that raged during the IAU's last assembly in 2006.

Pluto and its pals loomed over the stage when the International Astronomical Union kicked off its general assembly this week in Rio de Janeiro, three years after its controversial decision to reclassify the icy world as a dwarf-planet non-planet. But that's as close as the issue will get to the spotlight this time around.

Neither the pro-Pluto nor the anti-Pluto adherents have any interest in reviving the debate over planethood in Rio - and it'll likely be a long time before the IAU gets back into planetary politics.

"There's no discussion of dwarf planets. That has subsided," said Lars Lindberg Christensen, who served as the IAU's spokesman during the 2006 assembly in Prague and is filling the same role in Rio.

Like others among the thousands of attendees in Rio, Christensen noticed that depictions of the dwarf planets known as Pluto, Eris, Haumea and Makemake were projected above the stage during Tuesday's opening ceremonies. "I was sort of snickering about that," he admitted. But Christensen insisted that the display had no connection to the IAU's business this year.

"That issue was dealt with," he told me. "There will always remain some people who are skeptics, particularly in the North American part of the world, but people are returning to the science."

Among the anticipated headlines are fresh findings about the similarities between surface features on Earth and on Titan, Saturn's smog-shrouded moon, as well as new questions about the habitability of Earthlike planets around sunlike stars, Christensen said. However, there'll be no controversies that bring tears to the eyes of third-graders (unless there are some kids out there who really hate the Second Realization of the International Celestial Reference Frame).

No more pokes at Pluto

That's likely the way the IAU will play things for the foreseeable future, said Gettysburg College astronomer Laurence Marschall, a co-author of the recently published book "Pluto Confidential: An Insider Account of the Ongoing Battles over the Status of Pluto."

"Nowhere in the next 500 years are they going to deal with the definition of scientific terms," Marschall told me. "Maybe operational terms, like the definition of a dynamical second. But when it comes to scientific terms, they will probably wisely leave them to common usage."

Marschall belongs to a select group: the 400 or so astronomers who were actually in the room to vote on the IAU's planethood definition in Prague. He voted in favor of the final wording, even though the process was as ugly as an eruption on Io. "Given the course of action that the IAU took, the results were inevitable," Marschall said. "I would have voted for anything that recognized Pluto as being part of a new class of objects."

His co-author, astronomer/writer Stephen Maran, noted that one of the IAU's main reasons for pushing ahead with the planet definition was to set up a procedure for naming newfound objects like Pluto - relatively small, roundish objects such as Eris (a.k.a. Xena), which is actually bigger than the one-time ninth planet.

The procedure was indeed established: Names for dwarf planets are now approved jointly by the IAU's Committee on Small Body Nomenclature (which deals with asteroids and comets) and its Working Group for Planetary System Nomenclature (which deals with the moons and surface features of planets). However, that procedure could have been put into effect without ruling on the broader planet-or-not definition.

"Now it appears that everybody in the United States is an opponent of the IAU definition," Maran said, with just a bit of hyperbole. "Everybody pretty much agrees that the definition is not scientifically useful. It solves that administrative issue, but it has inflamed passions and raised the point that you don't normally adjudicate scientific questions in a court of law or a legislature."

No pitchforks for Pluto

So why aren't the definition's detractors descending on Rio with firebrands and pitchforks? According to those who put down Pluto, it's because they know they're in the wrong.

"I suspect no one will press the fight about Pluto because even the partisans are reluctantly admitting to themselves that the fight is over, and planets have won," Caltech astronomer Mike Brown, who was in on the discovery of Eris and two other dwarf planets, wrote in a blog entry from Rio. (His Twitter username, Plutokiller, lets you know where he stands.)

Speaking as one who's been in touch with Pluto's partisans, however, I'd have to say the reason is because they've moved beyond the IAU, just as the IAU has moved beyond Pluto. After three years of claiming that scientific questions can't be settled by a vote, why would the dissenters force yet another vote they see as meaningless? It'd be like Martin Luther pleading for a recount in the College of Cardinals.

"The IAU is not Holy Mother Church, speaking ex cathedra," Mark Sykes, director of the Arizona-based Planetary Science Institute and an advocate for Pluto's planethood, said in an e-mail sent as I was writing up "The Case for Pluto."

"The issue continues to be debated," Sykes observed. "Scientists continue to write papers where Pluto and other such objects are referred to and treated as planets, because the science being discussed (e.g., atmospheric processes, mantle convection, differentiation) are shared with objects like the Earth."

Alan Stern, a planetary scientist at the Colorado-based Southwest Research Institute and principal investigator for NASA's New Horizons mission to Pluto, turned down an invitation to speak at the IAU's Rio meeting. "I'm not there because the IAU seems to have become irrelevant," he told me today via e-mail.

Pluto in perspective

In their book, Marschall and Maran detail many other decades-long planetary debates - over the status of Ceres and other asteroids, for example, or the search for the planet Vulcan (fascinating!), or the arguments over who really discovered Neptune.

The IAU's actions back in 2006 will no doubt be incorporated similarly into the broader sweep of scientific history. (And humor as well. One of Marschall's favorite quips was something he saw on a bumper sticker: "They got Pluto, Uranus is next.")

So what kind of verdict will history render on the dwarf planets?

Marschall thinks that Pluto and its pals will be put in their proper perspective as scientists learn more about how solar systems are constructed.

"In our own solar system, the debate is over how we're going to group these various objects that circle the sun," he told me. "Eventually, we're going to think that there are these eight large bodies, and then there are all these little bodies between Mars and Jupiter and scattered out in that region, and then you've got these trans-Neptunian objects and the Oort Cloud out there. People aren't going to worry too much about what a planet is. You're just going to think about these things that are part of the retinue of the sun.

"But it's way too early to start thinking about that with extrasolar planets," he added. "It's going to take a long time before the pictures of those systems are fleshed out."

Maran thinks Pluto will eventually be accepted as a kind of planet once again, although he doubts that will come about as the result of a vote.

"What's going to happen is that scientists will continue to define planets as they see them," he told me. "The people left holding the bag are above all the schoolteachers, and to some extent the publishers and the journalists, who are not supposed to put themselves up as experts. They're supposed to apply some official usage, and there is nothing official except for the IAU. ... The one political body I can think of that could have a political impact on this would be the Texas school board. If they decide that there are nine planets for the schoolbooks, that's going to have a big impact."

But even the Texas school board would probably figure out that it's better to keep quiet on the subject, unless it's to make a joke.

"If you want to think of a project that can consume endless amounts of people's time and create unbelievable degrees of bad feeling, it's for any scientific body to begin a project to create an official dictionary of scientific terms," Maran said. "No one fights over the commercial dictionaries, but let it be an official dictionary of a body of scientists, and people who could be out there discovering new worlds will be indoors arm-wrestling over the definition of one term or another."

Then Maran had another thought: "It actually might be a good way to get professors in the current environment to retire and make their slots open for younger people - just appoint them to one of these commissions."

Update for 5:30 p.m. ET Aug. 6: I've updated my reference to Titan by linking to the IAU's news release about the research. The release notes that "wind, rain, volcanoes, tectonics and other Earthlike processes all sculpt features on Titan's complex and varied surface in an environment more than 100 degrees Celsius colder on average than Antarctica." That's too cold for water to work the way it does on Earth - but Titanian methane takes the place of water in the atmosphere and as precipitation, cutting channels in the surface terrain.

The Saturnian moon's volcanoes, meanwhile, appear to spew out slurries of water ice and ammonia.

"It has not escaped our attention that ammonia, in association with methane and nitrogen, the principal species of Titan's atmosphere, closely replicates the environment at the time that life first emerged on Earth," Robert Nelson, a senior research scientist at NASA's Jet Propulsion Laboratory, is quoted as saying.

More from the IAU General Assembly:

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