Physicist - Why Pluto was demoted

January 13, 2008|By TIFFANY ARNOLD

WAYNESBORO, Pa. - It's the announcement that changed the cosmos and still has people buzzing: Pluto is not a planet - it's a weenie "dwarf planet."

Gettysburg College physics professor Larry Marschall will discuss what led to Pluto's demotion to dwarf-planet status Thursday, Jan. 24 at Renfrew Museum and Park. The event, originally scheduled for Jan. 17, was postponed due to bad weather.

The Renfrew Institute will host the event in collaboration with Tri-State Astronomers. The free, public program starts at 7 p.m.

"I'm going to put the Pluto controversy in context," said Marschall in a telephone interview from Austin, Texas, while attending the American Astronomical Association's yearly meeting.

The Pluto controversy, Marschall said, is just one example of how science and society's understanding of outer space continues to evolve.


Marschall, deputy press officer for the American Astronomical Association, was in Prague when the International Astronomical Union determined by vote that Pluto no longer met its definition of a planet.

He wouldn't say how he voted.

"You'll have to come to the talk to find out that," said Marschall, an author and editor of Smithsonian Air & Space Magazine, who is working on a book about the Pluto controversy.

Even though more than a year has passed since the Pluto ordeal, the ex-planet still makes for good joke fodder. It even helped mint a new verb, "to pluto," which, according to the American Dialect Society, means "to demote or to devalue someone or something, as what happened to the former planet Pluto." The society cited "plutoed" as 2006's word of the year.

"There's a lot of sentimental attachment to Pluto," Marschall said. "There's more than just scientific issues there."

Changing the definition of what constitutes a planet has a broader social impact, Marschall said, as it alters people's understanding of what lies beyond planet Earth.

That's the reason that, when determining the fate of Pluto and some other Pluto-like objects, the International Astronomical Union consulted people outside the scientific community such as historians and science writers, Marschall said.

Still, even before its demotion to dwarf, Pluto's status as a planet was suspect.

"Pluto was kind of the red-headed aunt in the closet that nobody wanted to talk about," says Rod Martin, planetarium resource teacher for Washington County Public Schools and secretary of the Tri-State Astronomers. "(Pluto) didn't fit in."

Talks of demotion began to arise in recent years, when astronomers started discovering objects in our solar system that were either comparable in size to Pluto or even bigger, Marschall said.

In August 2006, the Astronomical Union revamped its definition of a planet. It decided that, in order to be called a planet, a heavenly body must have enough mass to be round (generally at least 200 miles in diameter), must orbit around the sun, and must be the dominant object within its orbit, Marschall said.

By that definition neither Pluto nor three other would-be planets recently called into question - Ceres, an asteroid between Mars and Jupiter; and Charon and Eris, objects near Pluto - met the criteria needed for bona fide planet-hood, according to the organization's online press materials.

The outcome: The solar system now has eight planets and four dwarf planets.

"This isn't the first time a planet has come and gone," Marschall said.

In the 1800s, for example, astronomers believed there were as many as 19 planets, of which most were really asteroids, Marschall said.

While Pluto's demotion stirred up a social buzz, it did not lead to a mass expungement of old text books, Martin says.

Instead, it has prompted healthy classroom discussions about the role of science.

"It forces (students) to see how science works, that science changes, evolves," Martin says. "There are no hard-and-fast rules."

If you go ...

WHAT: "Deconstructing Pluto," a lecture by Larry Marschall, a Gettysburg College physics professor who was present when International Astronomical Union determined Pluto was not a planet.

WHEN: 7 p.m. Thursday, Jan. 24 (rescheduled from Jan. 17)

WHERE: The visitor center of Renfrew Museum and Park, 1010 E. Main, St., Waynesboro, Pa. Enter at the Welty Road entrance, off Main Street. Parking is available off the Main Street entrance, near the barn, for people with special needs and disabilities.

COST: Free

MORE: Call Renfrew Institute, 717-762-0373, or go to

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