Pluto arrived on the public's consciousness in 1930 when Clyde Tombaugh, an Illinois farm boy turned astronomer, discovered the frigid world after an extensive search for a much-sought "Planet X."

		More coverage Graphic: Pluto's planetary status Astrologers undaunted by Pluto's demotion

Yesterday, however, Pluto's status as a planet came crashing hard to earth.

In its annual convention in Prague, Czech Republic, the International Astronomical Union revoked Pluto's planetary status under new guidelines meant to bring the definition of "planet" in line with our expanding technology.

Pluto doesn't make the grade under the new rule: "a celestial body that is in orbit around the sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a ... nearly round shape, and has cleared the neighborhood around its orbit."

Pluto is disqualified because its oblong orbit overlaps with Neptune's.

It will now be reclassified in a new category of "dwarf planets," similar to what long have been termed "minor planets." The definition also lays out a third class of lesser objects that orbit the sun -- "small solar system bodies," a term that will apply to numerous asteroids, comets and other natural satellites.

		Listen in Pluto in the doghouse: Dr. Bruce Hapke, University of Pittsburgh professor of geology and planetary sciences, discusses why the International Astronomical Society's decision to 'demote' Pluto is a good idea. Dr. Hapke offers understanding for those who may not like the demotion. Tom Reiland, longtime amateur astronomer, and founder and director of Nicholas E. Wagman Observatory, offers his observations on the IAU ruling. Mr. Reiland says he understands why the term 'planet' had to be redefined.

Astronomers feared that, by declaring Pluto and similar worlds such as its moon Charon, the largest asteroid Ceres and 2003 UB313 as planets, that the solar system in years to come might be overrun with planets as new discoveries are made. Ceres and 2003 UB313 qualify as dwarfs; Charon may not receive any special designation.

"I think it's probably a good thing," Dr. Bruce Hapke said of Pluto's demotion.

Dr. Hapke, professor emeritus of geology and planetary sciences at the University of Pittsburgh, studies the surfaces of planets and satellites by analyses of data taken from the Earth and by spacecraft. He was a member of the Mariner 10 and Viking imaging science teams.

"If we continue to call Pluto a planet, there's probably a lot of bodies the size of Pluto or larger out beyond the orbit of Neptune that we haven't discovered yet," Dr. Hapke said. "If you call Pluto a planet you'd have to call these things a planet, and we'd end up with a solar system with a hundred planets."

While the IAU's decision is deemed widely by the astronomical community as scientifically sound, it may not sit well with the general public, which has an affinity for Pluto and will have to rethink a solar system consisting of eight planets instead of nine.

"It's just a question of tradition," Hapke said. "People are always upset when tradition gets changed. But you have to change as you learn more about something."

Shaler astronomer Tom Reiland, founder and director of Nicholas E. Wagman Observatory operated by the Amateur Astronomers Association of Pittsburgh, has observed Pluto many times. He said it will be difficult not to think of Pluto as a planet, but the IAU's ruling makes sense.

"I have mixed emotions considering that for all my life I've known Pluto as a planet," he said. "But I can see their point of view."

It's likely that Mr. Tombaugh, who died in 1997, would have been disappointed with the IAU's decision. He described his discovery in a 1990 interview with the Pittsburgh Post-Gazette. He searched for about a year before he found Pluto.

"It got to be a pretty grueling project, pretty tedious. But I had a natural curiosity to see what was out there," Mr. Tombaugh said. "I realized the impact of my discovery in one terrific wallop in one split second. I realized what I had found all at once."

Mr. Reiland said the news from the IAU "is not that Earth-shattering." People have to realize "things are going to change over a period of time. Our understanding of what a planet is will probably change again."

NASA said yesterday that Pluto's demotion would not affect its $700 million New Horizons spacecraft mission, which earlier this year began a 9 1/2-year journey to the oddball object to try to unearth more of its secrets.

"We will continue pursuing exploration of the most scientifically interesting objects in the solar system, regardless of how they are categorized," Paul Hertz, chief scientist for the science mission directorate, said in a statement.

The decision at a conference of 2,500 astronomers from 75 countries was a dramatic shift from just a week ago, when the group's leaders floated a proposal that would have reaffirmed Pluto's planetary status and made planets of its largest moon and two other objects.

That plan proved highly unpopular, splitting astronomers into factions and triggering days of sometimes combative debate that led to Pluto's undoing. In the end, only about 300 astronomers cast ballots.

So it appears schoolchildren will have to learn a new mnemonic, something akin to "My Very Excellent Mother Just Sent Us Nectarines" to help them remember the planets -- Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

"I'm willing to go with eight" planets, Mr. Reiland said. "It makes it a lot easier to look at all the planets in one night.

"Being able to see something as far out as Pluto is something special."