Miércoles 30 de Agosto de 2006, Ip nº 168

Pluto Is Demoted to ‘Dwarf Planet’
Por Dennis Overbye

Pluto got its walking papers today.

Throw away the placemats. Grab a magic marker for the classroom charts. Take a pair of scissors to the solar system mobile.

After years of wrangling and a week of bitter debate, astronomers voted on a sweeping reclassification of the solar system. In what many of them described as a triumph of science over sentiment, Pluto was demoted to the status of a “dwarf planet.”

In the new solar system, there are eight planets, at least three dwarf planets and tens of thousands of so-called “smaller solar system bodies,” like comets and asteroids.

For now, the dwarf planets include, besides Pluto, Ceres, the largest asteroid, and an object known as UB 313, nicknamed Xena, that is larger than Pluto and, like it, orbits out beyond Neptune in a zone of icy debris known as the Kuiper Belt. But there are dozens more potential dwarf-planets known in that zone, planetary scientists say, and the number in that category could quickly swell.

In a nod to Pluto’s fans, the astronomers declared that Pluto to be the prototype for a new category of such “trans-Neptunian” objects but failed in a close vote to approve the name Plutonians for them.

“The new definition makes perfect sense in terms of the science we know,” said Alan Boss, a planetary theorist at the Carnegie Institution of Washington, adding that it doesn’t go too far in cultural terms. “We have a duty to satisfy the whole world.”

The vote completed a stunning turnaround from only a week ago when the assembled astronomers had been presented with a proposal that would included 12 planets, including Pluto, Ceres, Xena and even Pluto’s moon Charon. Dr. Boss said today’s decision spoke to the integrity of the planet-defining process. “The officers were willing to change their resolution and find something that would stand up under the highest scientific scrutiny and be approved,” he said.

Jay Pasachoff, a Williams College astronomer who favored somehow keeping Pluto a planet, said, “The spirit of the meeting was of future discovery and activity in science rather than any respect for the past.”

Mike Brown of the California Institute of Technology, who as the discoverer of Xena, had the most to lose personally from Pluto’s and Xena’s downgrading, said he was relieved. “Through this whole crazy circus-like procedure, somehow the right answer was stumbled on,” he said. “It’s been a long time coming. Science is self-correcting eventually, even when strong emotions are involved.”

It has long been clear that Pluto, discovered in 1930, stood apart from the previously discovered planets. Not only was it much smaller than them, only about 1,600 miles in diameter, smaller than the Moon, but its elongated orbit is tilted with respect to the other planets and it goes inside the orbit of Neptune part of its 248-year journey around the Sun.

Pluto makes a better match with the other ice balls that have since been discovered in the dark realms beyond Neptune, they have argued. In 2000, when the new Rose Center for Earth and Space opened at the American Museum of Natural History, Pluto was denoted in a display as a Kuiper Belt Object and not a planet.

Two years ago, the International Astronomical Union appointed a working group of astronomers to come up with a definition that would resolve this tension. The group, led by Iwan Williams of Queen Mary University in London, deadlocked. This year a new group with broader roots, led by Owen Gingerich of Harvard, took up the problem.

According to the new rules a planet meet three criteria: it must orbit the Sun, it must be big enough for gravity to squash it into a round ball, and it must have cleared other things out of the way in its orbital neighborhood. The latter measure knocks out Pluto and Xena, which orbit among the icy wrecks of the Kuiper Belt, and Ceres, which is in the asteroid belt.

Dwarf planets only have to be round.

“I think this is something we can all get used to as we find more Pluto-like objects in outer solar system,” Dr. Pasachoff said.

The final voting came from about 400 to 500 of the 2,400 astronomers who were registered at the meeting of the International Astronomical in Prague. Many of the astronomers, Dr. Pasachoff explained, had already left, thinking there would be nothing but dry resolutions to decide in the union’s final assembly.

It was hardly the first time that astronomers have rethought a planet. The asteroid Ceres was hailed as the eight planet when it was first discovered in 1801 by Giovanni Piazzi floating in the space between Mars and Jupiter. It remained a “planet” for about half a century until the discovery of more and more things like it in the same part of space led astronomers to dub them asteroids.

In the aftermath, some astronomers pointed out that the new definition only applies to our own solar system and that there was so far no such thing as an extra-solar planet.

The decision was bound to have both a cultural and economic impact on the industry of astronomical artifacts and toys, publishing and education. The World Book Encyclopedia, for example, had been holding the presses for its new 2007 edition until Pluto’s status could be clarified.

Neil deGrasse Tyson, director of the Hayden Planetarium in New York, said children are flexible, when asked about the cultural impact of today’s redefinition. He said that he had not bothered to watch the International Astronomical Union’s vote in the Internet, as many astronomers did. “Counting planets is not an interesting exercise to me,” he said. “I’m happy however they choose to define it. It doesn’t really make any difference to me.”

Dr. Tyson said the continuing preoccupation with what the public and schoolchildren would think about this was a concern and a troubling precedent. “I don’t know any other science that says about its frontier, ‘I wonder what the public thinks,’ ” he said. “The frontier should move in whatever way it needs to move.”

  24/08/2006. The New York Times.