by Playfuls Staff |
16th August 2006
The International Astronomical Union is set to find a new definition of the word planet this week, which should totally modify our perception upon our Solar System. Following astronomers’ decision, Pluto should remain a planet, but a few others will join it soon.[more]
Planets should be defined as objects that have sufficient gravity to form a “nearly round” shape and that orbit a star without themselves being a star or a moon, according to the draft of a resolution published today on the Web site of the Paris- based International Astronomical Union (IAU).
The new definitions will leave eight "classical planets" - Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Everything else, including Pluto, which was named the ninth planet when it was discovered in 1930, will be a pluton.
The proposal was hammered out after two years of intense debate among leading experts of the IAU, which is the sole authority on Earth for naming celestial objects.
"We now have a new way to put the solar system together," said Richard Binzel, a member of the IAU executive committee that drafted the definition. "We think this definition is reasonable."
On the other hand, some astronomers think that this new definition will render the old manuals and textbooks useless, but it will also create more confusion.
"It's a mess," said Michael Brown of the California Institute of Technology.
The new definition of the term “planet” would increase the number of planets in our Solar System to 12 from the nine that are taught in schools, with the inclusion of Ceres- an asteroid orbiting between Mars and Jupiter, Charon, which for now is considered Pluto's moon, and so-called 2003 UB313, an object beyond Pluto. Other bodies outside the orbit of Pluto and Neptune will also be considered.
The proposal from Prague admits the existence of eight classical planets, three planets belonging to a new category called "plutons" and the largest asteroid Ceres.
Pluto remains a planet, but becomes the basis for the new pluton category.
"For the first time in more than 75 years, we will be able to discover new planets in our Solar System. This is a fascinating prospect," said Richard Binzel, a member of the IAU planet definition committee which put together the proposal.
Dr Andrew Coates of the Mullard Space Science Laboratory in Dorking said he thought the plan was "a good compromise".
"On the second morning several members admitted that they had not slept well, worrying that we would not be able to reach a consensus," writes Owen Gingerich of the Harvard-Smithsonian Center for Astrophysics and chair of the Planet Definition Committee. "But by the end of a long day, the miracle had happened: we had reached a unanimous agreement."
The Solar System thus enriches itself with the first double planet, the Pluto-Charon pairing, as well as several so-called "dwarf planets," such as Ceres, which, although only 952 kilometers in diameter, still fulfills the new planet criteria.
In fact, there are at least 12 more planet candidates, including Sedna and Quaoar that the IAU will be called upon to include or dismiss during future deliberations, along with giving 2003 UB313 a proper name. For the moment, attendees will simply debate the proposed definition and vote on whether to accept it or not on August 24.
"Did our committee think of everything, including extrasolar planet systems? Definitely not!" Gingerich wrote. "Science is an active enterprise, constantly bringing new surprises."
Dr Andrew Coates of the Mullard Space Science Laboratory in Dorking explained: It keeps the idea of eight classical planets, while Pluto is allowed to retain its status. But other objects are allowed in, which I suppose makes life more interesting."
“These trans-Neptunian objects bigger than Pluto created a nomenclature crisis,” Owen Gingerich, Professor of Astronomy and History of Science at the Harvard-Smithsonian Center for Astrophysics, and chair of the committee that devised the draft resolution, said yesterday in a telephone interview from Prague. “We were keen to avoid an arbitrary decision on defining planets and to make a decision that was based on science.”
The threshold for planetary status that the IAU-appointed committee decided on was bodies with a mass greater than 500,000,000,000,000,000,000 kilograms and a diameter over 800 kilometers (497 miles). That means that Pluto, at 2,300 kilometers across, classifies as a planet - an idea that many oppose, according to Gingerich.
Under the proposal put forward by a seven-member Planet Definition Committee, plutons will be considered objects in the outer regions of the solar system that are Pluto-sized or bigger. They also have orbits that are different from their "classical" companions and typically take more than 200 years to orbit the Sun.
“There was a considerable difference of opinion: a large number of astronomers hoped that Pluto would not be included,” Gingerich said. The seven-person committee that drafted the resolution, whose members included Dava Sobel, author of the bestseller “Longitude,” was also split initially, he said.
“We never asked `how many of you want to wipe Pluto out and how many want to keep it?' but there were people from both camps in the committee,” with two saying Pluto should be a planet, two saying it shouldn't, and three holding neutral stances, Gingerich said. The final decision was “unanimous,” he said.
If it's passed, original committee member Chris Tinney - an astronomer with the Anglo-Australian Observatory in Sydney - will be delighted.
"I will be deliriously happy when I no longer have to spend a moment of my time worrying about the definition of the word 'planet'," Dr Tinney said last year when The Australian flagged the upcoming resolution.
Gibor Basri, chairman of astronomy at the University of California, Berkeley, praised the IAU for coming up with a reasonable definition that could help quell the stubborn arguments over what makes a planet, a debate provoked by critics who questioned tiny Pluto's status as a planet.
"I feel that they have made the most rational and scientific choices," he said. "It does mean some adjustment for the public."
“It is wonderful when new scientific discoveries present you with new problems," said Richard Binzel , a Massachusetts Institute of Technology professor of planetary geology who served on the panel. “This is almost the essence of being a scientist.”
Professor Owen Gingerich, who chairs the IAU planet definition committee, said: "In a sense we're demoting Pluto by taking it off the list of classical planets. But we're promoting it by making it the prototype of this new category of plutons."
Dr Coates commented: "Something had to be done about the definition. It does change the textbooks somewhat, but it also demonstrates that this is a vibrant area of research.
"The surprise is Ceres, because most people thought of it as an asteroid."
Ceres is the largest object in the asteroid belt between Mars and Jupiter, and like a planet is spherical in shape.
It's also an open question how the new definition would be received by the public, who grew up with mobiles of the nine-planet solar system in their bedrooms and learning mnemonic devices to memorize the planets.
