ROANOKE TIMES
Copyright (c) 1996, Roanoke Times
DATE: Friday, March 8, 1996 TAG: 9603080090
SECTION: NATL/INTL PAGE: C7 EDITION: METRO
SOURCE: KATHY SAWYER THE WASHINGTON POST
For the first time since the mysterious, remote planet Pluto was discovered 66 years ago, astronomers have seen its surface directly.
New images from the Hubble Space Telescope, released Thursday, reveal the only unexplored planet in the solar system to be an unexpectedly complex object that ``really blew our doors off,'' said Alan Stern of the Southwest Research Institute in Colorado, leader of the observing team. ``Pluto is turning out to be a wonderfully exciting place.''
The images show almost a dozen ``provinces'' of contrasting dark and light, including a ragged northern polar cap split by a dark strip. Nobody knows yet what these dark and light splotches are, the researchers said, but most of them are probably complex patterns formed by frosts that migrate across the surface with changing Plutonian seasons. Stern called them ``Boston snow [dark] and Colorado snow [light].''
Some of the features may also be basins, impact craters and other topographic features. The only way to be sure is to send a spacecraft there, Stern said.
Just two-thirds the size of Earth's moon, and at least 12,000 times farther away, Pluto has never appeared as anything more than a fuzzy point of light in even the largest ground-based telescopes. Astronomers were unable to study it with much success before the late 1970s.
Advances since then have been based mostly on measurements of its reflected light and of its interactions with its moon Charon, first detected in 1978 and visible as a speck in some of the Hubble images. (The size of Pluto as seen from Earth, the researchers said, is such that it would take 18,000 Plutos in a line to match the diameter of the full moon.)
Named after the Roman god of the underworld, Pluto is so unusual it ``defies classification,'' the scientists noted.
Dwelling in the frontier where the planets peter out and a belt of orbiting rubble begins, it is about 70 percent rock, with a covering of ice and volatile chemicals. It has been compared in some ways to Neptune's large moon Triton and in other ways to a comet.
Some planetologists describe it as an ``ice dwarf,'' the last survivor of a lost population of small, icy objects that inhabited the primeval solar system. Although it is officially classified as a planet, some astronomers refuse to call it that.
``It's a planet,'' said Stern, invoking the ``quacks-like-a-duck'' rule. ``It's round, it has a satellite and an atmosphere.'' He said recent claims to the contrary are ``at best a minority opinion'' and have done ``a real disservice to a lot of schoolchildren, and to grade-school science teachers who are now going to have to go and re-explain [the issue] over and over to all those little kids.''
The Hubble views of Pluto, taken when the planet was about 2.8 billion miles away, are comparable to counting the spots on a soccer ball at 400 miles. The team had to push the orbiting telescope to its limits to get them, scientists said at a briefing at NASA headquarters. The pictures still leave much to the imagination, but they lay the groundwork for better maps and perhaps, in the next decade, the first robot explorer from Earth.
``These images are just fabulous,'' said Bruce Margon, an astronomy professor at the University of Washington in Seattle. The view of Pluto is ``a real surprise ... because of this unexpected blotchiness.'' Also exciting, he said, is the prospect that ``it's going to change and we're going to be able to watch the evolution of an entire planetary atmosphere in a controlled way its chemical ices.
The Hubble used its Faint Object Camera to take more than a dozen snapshots covering almost the entire surface, as Pluto rotated on its axis through a complete ``day,'' (equal to 6.4 Earth days) in June and July 1994.
``These results ... are much better than I ever hoped for. Hubble has brought Pluto from a fuzzy, distant dot of light to a world which we can begin to map,'' said team member Marc Buie of Lowell Observatory in Arizona. He said the data in the images will produce a crop of new Pluto studies.
Pluto and Charon travel in an egg-shaped orbit that takes 248 years to complete. It carries them as far as 4.6 billion miles from the sun (49 times as far out as Earth), making it the outermost planet for all but 20 years of its orbit. During that period, its eccentric path brings it inside the orbit of Neptune, the next most remote planet, and as close as 2.8 billion miles to the sun. That's still 29 times as far out as Earth. Pluto's last close approach to the sun came in 1989.
These swings from big chill to deep freeze produce seasons on Pluto, where the current fading summer is maintaining relatively ``balmy'' surface temperatures estimated to range from minus 380 to minus 350 degrees Fahrenheit. This fleeting warm spell likely sets up tremendous pressure differences at the surface, the researchers said, creating high winds in the fragile atmosphere. The atmospheric pressure at Pluto's surface is likely about a millionth that of Earth.
Scientists believe Pluto, in effect, ``launders'' its surface. The ice is gradually tarnished over the years by ultraviolet sunlight and cosmic rays. As the planet moves closer to the sun, this dirty, old ice evaporates, revealing a nice clean surface.
As Pluto moves away from the sun, much of its atmosphere freezes and falls to the ground in a fresh layer of white frost. This loss of the planet's atmosphere causes all weather to cease, as Buie put it, until the next swing back toward the sun.
Pluto is headed back out into the outer edges of the solar system but will not recede beyond the orbit of Neptune until 1999. NASA's Jet Propulsion Laboratory has proposed to build and dispatch a spacecraft called the Pluto Express in a few years. Mission planners say they want to reach their destination before its atmosphere collapses again.
Stern suggested they may be aided by one of the features revealed in the Hubble images of Pluto: It is the clear silhouette of Mickey Mouse - or is it Minnie? - in one of the bright ``Colorado snow'' regions. ``Maybe Disney will help fund the Pluto Express.''
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