The International Astronomical Union altered the definition of a planet, stripping Pluto of its status. Pluto, seen at far right in the image above, now is included in a new category known as dwarf

The fall of Pluto from the list of major planets left Kansas University astronomers crestfallen Thursday.

“Clyde Tombaugh will no longer be called the discoverer of the ninth planet,” said Barbara Anthony-Twarog, professor of physics and astronomy.

In a historic action, the International Astronomical Union convening in Prague, Czech Republic, set new rules for what defines a planet. That tossed Pluto from the list of “classical” planets and put it among a new category of “dwarf planets.”

And the demotion will force KU to rethink the way it celebrates Pluto’s Jayhawk discoverer, alumnus Clyde Tombaugh.

“It’s a pleasure for us to talk about Clyde Tombaugh’s heritage at KU and we still will,” Anthony-Twarog said. “But it’s a different conversation now.”

Tombaugh earned bachelor’s and master’s degrees from KU after discovering Pluto while working at Lowell Observatory near Flagstaff, Ariz.

KU faculty and students for years have delighted in the telling of Tombaugh’s story.

A farm boy from rural Burdett, the young Tombaugh once built a telescope with old tractor and auto parts. In 1930, at age 24, he discovered Pluto. The discovery fueled a distinguished career for Tombaugh.

And KU has treasured his legacy. Scholarships bear his name, as does an observatory. Earlier this year, KU threw a posthumous 100th birthday celebration for Tombaugh.

But on Thursday, it was hard for some not to feel like the party balloon had been popped.

“It’s upsetting,” said Bruce Twarog, professor of astronomy and physics. “We knew Clyde. He was a very strong promoter of astronomy for the public.”

Defining the issue

Some at KU had hoped the International Astronomical Union would define a planet as a spherical object that independently orbits the sun. That definition would have kept Pluto in the mix but possibly added countless others.

The definition favored by KU astronomers was under consideration – as revealed in a draft definition last week – but the scientists meeting in Prague ultimately rejected it.

“It was an open-ended definition,” Anthony-Twarog said. “And I suspect that is what people found uncomfortable. We went from nine to 12 planets last week, and who knows how many more would have been discovered in the next decades.”

Instead, the convention settled on this definition: “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.”

In this 1980 photo provided by Dale Wittner, Clyde Tombaugh is shown in Las Cruces, N.M., with a telescope similar to one he used to find Pluto decades earlier.

About 2,500 astronomers from 75 countries were at the conference. In the end, after a long and sometimes combative debate, only about 300 of them cast ballots.

Pluto lost its previous status because its oblong orbit overlaps Neptune’s. The change leaves the number of major planets down to eight: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

The new definition also sidelined two other objects that at one point were moving toward full-fledged planethood.

Joining Pluto as dwarf planets are the asteroid Ceres, which was a planet in the 1800s before it was demoted, and 2003 UB313, an icy orb slightly larger than Pluto and nicknamed “Xena” by its discoverer, Michael Brown of the California Institute of Technology.

In Prague, some scientists made clear they were as sentimental as anyone else about the ninth rock from the sun.

Jocelyn Bell Burnell, a specialist in neutron stars from Northern Ireland who oversaw the proceedings in Prague, urged those who might be “quite disappointed” by Pluto’s demotion to look on the bright side.

“It could be argued that we are creating an umbrella called ‘planet’ under which the dwarf planets exist,” she said, drawing laughter by waving a stuffed Pluto of Walt Disney fame beneath a real umbrella. Later, she hugged the doll as she stood at the dais.

NASA journey continues

NASA said Thursday 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 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.

KU junior Julie Feldt, an astronomy major, said Tombaugh’s story intrigued her when she first visited KU.

“It’s kind of sad because maybe it might not be as significant or important anymore,” she said.

But KU astronomy faculty said they would continue to celebrate Tombaugh.

“I think we will still honor the anniversary of the discovery of Pluto and talk about it as the first discovered object in this enormously important class of objects and one of the largest minor bodies in the solar system,” Anthony-Twarog said.