The planet that gets no respect - for now

Mark Sykes knows that Pluto is slipping away.

Just 12 years ago, the errant chunk of ice and rock was as close to Earth as it ever gets - swooping inside even Neptune on its odd, elliptical path around the sun. The time was right, it seemed, for humans to finally visit this last unexplored outpost in their solar system.

Plans were made and designs were drawn. The probe would launch in 2004 and rendezvous in 2012, catching Pluto before its oblong orbit took it billions of miles farther into the darkness of space.

Then came the great setback. In September, NASA halted the project, calling it to too expensive. Now, as Pluto loops away, amateurs and scientists like Dr. Sykes are desperately trying to rescue the mission with Web campaigns and project redesigns, knowing that a similar opportunity to study our most mysterious neighbor won't arise again for 200 years.

"There has been a rallying around this project because of the closing window of opportunity," says Sykes, an astronomer at the University of Arizona in Tucson. "If we only have one chance to do this mission, people are going to be much more motivated to do it."

The race is already on. Although NASA put its plans on hold, it has told members of the science community they can have until March 21 to come up with an alternate that costs less than $500 million for the fly-by photo shoot. If NASA finds a proposal to its liking, production could begin this year.

So far, half a dozen teams from physics labs and aerospace companies around the United States have joined the effort. One high school senior in Pennsylvania has even dedicated his website to saving the mission.

It's a tight deadline, participants say, but they understand why timing is crucial. For one, if scientists wait too long, Pluto's anemic atmosphere could freeze and fall out of the sky.

The very fact the Pluto has an atmosphere intrigues astronomers. For years, many people had thought Pluto was little more than a piece of space junk caught in the sun's gravity. Yet in 1988, a study detected some gases and vapors clinging to Pluto, which is about two-thirds the size of the moon.

With each passing day, however, the planet is getting colder as it moves farther from the sun. Soon, some astronomers say, nearly all of the gases that make up the atmosphere could fall out of the sky as a Plutonian snowfall.

It's a problem brought about by Pluto's enigmatic behavior. Unlike the solar system's other planets, which follow a roughly circular route, Pluto's track is an off-center oval. From 1979 to 1999, this path took Pluto slightly closer to the sun than Neptune. By 2113, however, the circuit will take Pluto to a point nearly 2 billion miles farther away from the sun than Neptune.

At that distance, the sun would be little more than a bright star in a dark sky, and temperatures could drop below minus 400 degrees F., causing the freeze-out.

"The atmosphere could get so cold that you get something catastrophic and everything just freezes," says Ralph McNutt, a scientist at Johns Hopkins University's Applied Physics Laboratory in Laurel, Md., which is putting together a proposal for NASA.

To be sure, studying the atmosphere is not the only reason for going to Pluto. But the passage of time would make study of the planet difficult for other reasons, as well.

Foremost among them is available sunlight. In another oddity, Pluto is flipped on its side so the planet doesn't spin on a nearly vertical axis like Earth, but rather rolls like a barrel. The way the planet is situated, the sun hits only the top - the poles - during the winter, meaning that only one hemisphere gets light. In summer, the planet has swung around so that its sides are exposed to sunlight, with the sun rising west to east.

Right now, Pluto is moving toward fall. Come winter, half the planet will be dark and hard to photograph.

"The longer we wait, the worse it's going to be," says Sykes.

Indeed, the next time Pluto will be in summer and closest to the sun will be in the 23rd century. And while everyone agrees that a winter trip to Pluto would still yield valuable data, the focus is on getting there as soon as possible.

After all, Pluto is almost a complete mystery, and scientists know that worlds are almost always more varied and dynamic than imagined. For example, when the Voyager spacecraft passed Neptune in 1989, geysers of some unidentified material were spouting from the surface of Triton, a Neptunian moon thought to been barren and similar to Pluto.

Already, one scientist has posited that Pluto's moon, Charon, may be geologically active, with watery eruptions through an ice crust. But even the strongest telescopes see Pluto and Charon only as indistinct blobs, and any journey there will be an education.

"The very earliest history of the solar system is out there," says Tom Morgan, a NASA planetary scientist in Washington. "A lot of this is basically exploring the unknown." Enigmatic Pluto

One trip around the sun takes Pluto 248 years; a season lasts 62 years.

Pluto's character is so abnormal that the Rose Center for Earth and Space in New York no longer calls it a planet.

Pluto is half the size of the second-smallest planet, Mercury.

Pluto's moon, Charon, is half the size of the planet.

Pluto and Mercury are the only planets that have elliptical, not circular, orbits.

From 1979 to 1999, Pluto was closer to the sun than Neptune. By 2113, it will be nearly 2 billion miles farther away.

At Pluto's farthest point from the sun, sunlight takes seven hours to travel the 4.6 billion miles. (Sunlight reaches Earth in eight minutes.)

Scientists estimate surface temperatures on Pluto can reach minus 400 degrees F.

(c) Copyright 2001. The Christian Science Publishing Society