UH discovery could mean change for solar system
The debate is also affecting astrologers
When Bishop Museum planetarium manager Carolyn Kaichi begins explaining the universe to schoolchildren, she asks them, "How many planets are there in the solar system?"
"Nine," is the usual answer.
But that may all change next week, when the solar system could have 12 planets under a proposal scheduled to be voted on next week by the International Astronomical Union.
Under a draft proposal, the nine current planets -- including Pluto -- would be joined by the asteroid Ceres, Pluto's moon Charon, and a recently discovered object officially known as 2003 UB313 and nicknamed Xena.
Michael Brown of Caltech, Chadwick Trujillo of the Gemini Observatory atop Mauna Kea in Hawaii and David Rabinowitz of Yale discovered Xena three years ago and named it after the television heroine.
Next week's vote is the culmination of years of controversy over whether Pluto really is a planet -- a debate sparked by a discovery 14 years ago using the University of Hawaii telescope on Mauna Kea of an object called 1992 QB1 in what is now known as the Kuiper Belt.
"The result of that discovery is that we immediately knew Pluto is not special," said UH astronomer David Jewitt, who with Jane Luu made the discovery.
Even though he may have stirred up the debate, Jewitt believes the issue of whether Pluto is a planet is a matter of semantics and not of cosmic importance.
"Scientifically, it's a big nothing," Jewitt said. "Is it a boat or is it a ship? It doesn't matter. ... Understanding the solar system is more important than memorizing the nine planets."
But what the IAU decides will matter to publishers of encyclopedias, school textbooks, and science teachers who have been hanging solar system mobiles based on nine planets from classroom ceilings for generations.
The mnemonic phrase for remembering the order of the planets -- My Very Energetic Mother Just Served Us Nine Pizzas -- will also change, Kaichi pointed out.
The new order from the sun would be Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Charon and Xena or 2003 UB313.
Learning about the planets and the solar system is one of the first steps to understanding the universe, Kaichi said.
"(The solar system) is our neighborhood," Kaichi said. "Our world has expanded."
What the IAU does will also have an impact on astrologers, who use the nine planets to chart their predictions.
"We've always made this conjecture that there are two other planets out there that haven't been identified," said Cheryl Niggle, an astrologer and owner of the Serendipity book store on King Street.
As science advances, astrology also changes, Niggle said, adding that astrologers will probably meet as a body and come up with a new way to assign planets to the 12 signs in the zodiac.
Even if the proposal is approved by more than 2,000 astronomers from 75 countries meeting in Prague, the list of planets may grow even larger over the next few years.
Since Jewitt's discovery, more objects similar to QB1 have been discovered, including Xena. Xena is larger than Pluto and has a moon, nicknamed Gabrielle, that was discovered using the Keck telescope on Mauna Kea.
Many other objects will probably be added to the ranks of planets, scientists said. The panel in Prague provided a list of leading contenders that includes the recently discovered Sedna, Orcus and Quaoar, in the Kuiper Belt, as well as the large asteroids Vesta, Pallas and Hygiea.
The proposed new definition of a planet is any round object larger than 800 kilometers (nearly 500 miles) in diameter that orbits the sun and has a mass roughly 1/12,000th that of Earth. Moons and asteroids will make the grade if they meet those basic tests.
Roundness is key, experts said, because it indicates an object has enough self-gravity to pull itself into a spherical shape. Yet Earth's moon wouldn't qualify because the two bodies' common center of gravity lies below the surface of the Earth.
The IAU panel also proposed a new category of planets called "plutons," referring to Pluto-like objects that reside in the Kuiper Belt, a disc-shaped zone beyond Neptune containing thousands of comets and planetary objects. Pluto itself and two of the potential newcomers -- Charon and 2003 UB313 -- would be plutons.
Ceres, named for the Roman goddess of agriculture, would be a regular planet.
Astronomers also were being asked to get rid of the term "minor planets," which long has been used to collectively describe asteroids, comets and other non-planetary objects. Instead, those would become collectively known as "small solar system bodies."
IAU President Ronald Ekers said the draft definition, two years in the making, was an attempt to reach a cosmic consensus and end decades of quarreling. "We don't want an American version, a European version and a Japanese version" of what constitutes a planet, he said.
The current model of the solar system has held since 1930, when Pluto was discovered.
The proposal still could change before the vote on Aug. 24. Two brainstorming sessions are scheduled before the vote and there is still much controversy over whether Pluto should remain a planet.
Kaichi said she will teach whatever the astronomers decide, even if it means changing the current planetarium show.
The debate, Kaichi said, is a reminder that science evolves.
"Science is something we should consider as a changing, expanding type of endeavor," Kaichi said.
The Associated Press, the Boston Globe and the San Francisco Chronicle contributed to this report.