Pluto Safe From Demotion

"There is no plan to 'downgrade' or 'demote' Pluto," says Brian Marsden, head of the International Astronomical Union's Minor Planet Center. "It will stay as a planet."

Sometime early this year, it's likely Pluto will be designated a "transneptunian object" -- but not lose its planetary status, as has lately been rumored.

The designation, new for Pluto, already describes a group of 90 known bodies on the outer fringes of the solar system.

"This is like giving it a social security number," Marsden said. "Humans acquire names soon after birth. Later they get social security numbers. Does having the latter demote them in some way? Of course not."

Controversy has swirled around the pint-sized planet for various reasons, including its smallness and eccentric orbit. But the possibility of its being demoted touched nerves.

Among the miffed was Patricia Fort Johnson, a former resident of Streator, Ill. Pluto's discoverer, Clyde Tombaugh, was born near there.

Tombaugh attended high school in Burdett, Kan., and went to school at the University of Kansas, in Lawrence, so the possible demotion rankled folks in those towns, too. At KU, an observatory is named after Tombaugh.

Johnson recently wrote to Steve Shawl, KU professor of physics and astronomy, about her distress.

"I would be sorely disappointed," she told Shawl, "if Pluto were to be demoted from planet status. Where would be our truth?"

It was Shawl who put her in contact with Marsden, who responded with assurance and the social security analogy.

All this amounts to quite a bit of fuss over an odd little ball. Pluto is only about 1,450 miles across, about the distance between Kansas City and Las Vegas. It's considerably smaller than Earth's moon, which is about 2,150 miles across.

That's only one reason some people don't consider it a planet. Another is that it breaks a trend in the solar system, says Bruce A. Twarog, KU professor of physics and astronomy. While the inner planets, out to Mars, are basically orbiting rocks, the outer ones are gigantic gas balls -- until you get to Pluto, says Twarog.

If you drilled from the surface of Pluto toward its center, you'd be boring through ice the first quarter of the way. It's nothing you'd want to put into a margarita though, being frozen nitrogen, carbon monoxide and methane.

Currently, Shawl says, Pluto has a thin atmosphere. That's only because it's as close to the sun as it ever gets, and the heat is changing some of the ice into gas.

Pluto orbits the sun every 248 years, moving, unlike other planets, in a big ellipse rather than a circle.

For about 20 of those 248 years, it's closer to the sun than Neptune, which is ordinarily the eighth planet out from the sun, Shawl says. In fact, Pluto has been the eighth planet since Jan. 21 ,1979, but becomes the ninth planet again on Feb. 11 of this year -- and the pro-Pluto crowd can breathe a sigh of relief that it will still be a planet on that date.

Despite Pluto's eccentricities, the debate about whether it's a planet is "much ado about nothing," Shawl says.

David Tholen, a KU graduate now at the University of Hawaii, adds, "Debating the dividing line between planet and minor planet, or asteroid, is like debating the dividing line between city and town, river and stream."

"It's nothing that should send anybody out of orbit," Shawl says.