SAN DIEGO - The fate of Pluto and possibly dozens of potentially "new" planets hangs in the balance this week, thanks, in part, to North San Diego County.

It was just a year ago that Cal-Tech scientist and planet hunter Mike Brown announced he had discovered a 10th planet, larger than Pluto and nicknamed "Xena," by painstakingly reviewing pictures taken in 2003 by the 200-inch mirror of Palomar Observatory's Samuel Oschin telescope - images so far away they had not been seen before.

The discovery fueled an increasingly public debate over how to re-shape the solar system, a debate that could end Thursday when the world's most prestigious astronomical society meets in Prague, Czechoslovakia.

On Thursday, the astronomical union's members are scheduled to decide whether to ignominiously dump Pluto from Earth's solar system or to open the doors of planethood to as many as 50 new "planets" in this solar system.

On Monday, Palomar officials, North County star watchers and Brown's graduate assistant said they had different feelings - including excitement - about the planetary debate and the publicity.

"I think it's a big deal anytime we get people excited about astronomy or any science," said Bob Thicksten, superintendent of the Palomar Observatory. "And it's nice to wake up everyone once in a while to the fact that Palomar is in the backyard of more than 2 million people in San Diego County."

Brown could not be reached Monday, as he was flying back to California from Hawaii where he was conducting research about how to find a way to "remove" the visual interference the earth's atmosphere creates, according to assistants.

Thicksten said that study has excited the scientific community because it could one day allow earth-bound telescopes to take pictures with the same visual clarity now obtained only by spacecraft.

Kristina Barkume, who has been Brown's graduate assistant for four years, said Monday that astronomers have debated whether Pluto - the smallest and, most often, the most distant, of the current solar system's nine planets - should be considered a planet. Pluto was discovered in 1930 by Clyde Tombaugh, but debate has always centered around whether it was simply too small to be considered a planet - criticism that has resurfaced because of Brown's discovery of "Xena."

"It had been brewing for quite a while," Barkume said, "but it really came to a head when Mike (Brown) found this object."

Barkume said that scientists really have not had any set definitions for what a planet is, other than the simple rule that they - unlike stars - move, around the sun, or other stars.

Unfortunately, as telescopes have increased man's ability to see farther into the universe, scientist have found more objects that could fit into the description.

"Xena," which Brown discovered last year, is one of what Brown himself said are dozens of potential planets in what is known as the Kuiper Belt, a vast swarm of objects beyond Neptune.

Astronomers could dump Pluto. Barkume said there is precedent. The largest known asteroid in Earth's solar system, Ceres, was once considered a full-fledged planet, Barkume said, but that designation was dropped 150 years ago.

However, Barkume said that the general public has balked at the idea of demoting or dumping Pluto.

She said that she thinks the idea uncomfortably challenges people's understanding of their universe. People grew up knowing there were nine planets, she said, and they're comfortable knowing there are nine planets.

"They felt an affinity for Pluto. It was the oddball," Barkume said, referring to the fact it was the smallest and remotest planet. "It was kind of the underdog."

Consequently, a committee from the astronomical union has proposed a new planetary definition - one that will allow Pluto to stay, Xena to be recognized, Ceres to be reinstated and Pluto's moon Charon to be named a planet.

Brown says the basic definition the committee proposes is to include anything in space that is large enough to have its gravity "pull it into a ball" and circle a star.

Ironically, Brown - who is not a member of the astronomical union and has no vote - hates the proposal, calling it the "leave no ice ball behind" initiative.

Although the committee says its proposal would only recognize 12 planets - the current nine plus Ceres, Xena and Charon - Brown says the Kuiper Belt contains 50 objects that could qualify, and shudders at the idea of teachers trying to get children to remember 50-odd planets.

Others, however, were simply excited by all the planetary debate.

Craig Weatherwax, owner of Oceanside Photo and Telescope, which he said was the largest astronomic retail store in the country, said stargazers coming into his store were definitely buzzing.

"I think it's exciting," he said. "It creates some interest and enthusiasm about a science that is probably as old as the earth is. They were studying the skies back in prehistoric days. This is the first new planet in all my years. This is quite a phenomenon."

- Contact staff writer Gig Conaughton at (760) 739-6696 or gconaughton@nctimes.com.