Pasadena, Calif. ? Few planet hunters stand to gain as much as Michael Brown if our solar system balloons to 12 planets under a new definition. He’s spotted more than a dozen objects that might qualify as planets.

So why is he upset?

“When I was a kid, planets were special,” he said. “This definition takes the magic out of the solar system.”

It was Brown’s discovery of an icy rock bigger than Pluto that helped lead astronomers to rethink their definition of what a planet is. But Brown doesn’t think his discovery – or even Pluto, which was spotted in 1930 – should qualify as true planets.

On his Web site, the California Institute of Technology astronomer muses about why Pluto has kept its title for so long: “I think that astronomers are as sentimental as the rest of the world and couldn’t stomach removing Pluto. Probably they also couldn’t stomach the criticism that would follow.”

Last week, a high-ranking panel from the International Astronomical Union proposed that the solar system be expanded to 12 planets from the current nine, the first attempt at creating a scientific definition for planets.

Under the proposed definition, an object is a planet if it is at least 500 miles in diameter, orbits the sun and has a mass at least about one-12,000th that of Earth.

Pluto would keep its planethood while three other bodies would be added, including Pluto’s moon Charon, the asteroid Ceres and Brown’s object 2003 UB313, which he nicknamed Xena.

Michael Brown, an astronomer at the California Institute of Technology in Pasadena, Calif., helped lead astronomers to rethink their definition of a planet through his discovery of an icy rock bigger than Pluto. But Brown doesn't think his discovery, or even Pluto, should qualify as a true planet.

Brown said the proposal – that a planet is basically anything round orbiting the sun – is too broad and amounts to “No Ice Ball Left Behind,” cheapening the solar system.

He worries that by the time his daughter, Lilah, now 13 months, is old enough to memorize the planets, there could be hundreds.

In scientific circles, Brown is a star known for his outspokenness. But vocal as he is, he is not a member of the professional astronomers’ group and will be shut out of Thursday’s vote on the proposal.

“I feel like an outsider. It’s an odd situation,” said the 41-year-old, who was named one of Time Magazine’s 100 Influential People of 2006.

Still, his discovery helped initiate the process.

Brown grew up in Huntsville, Ala., nicknamed “Rocket City” because it is the home of NASA’s Marshall Space Flight Center. As a kid, he would hear rocket test firings and knew early on that he wanted to be an astronomer.

By Brown’s own count, 14 of his discoveries besides Xena are in the running for planethood. That could make Brown the most prolific planet hunter.

But he supports an eight-planet solar system, although he wouldn’t mind if Xena was added as the 10th planet.

“When people finally realize the number of planets is going to be much bigger, they’ll shake their heads and say, ‘Astronomers are crazy,'” Brown said.