Newly discovered craters on moon could hold eons-old lunar ice

May 27, 1994|By Frank D. Roylance | Frank D. Roylance,Sun Staff Writer

The Clementine spacecraft -- the first scientific mission to the moon in 22 years -- has discovered craters at the lunar south pole that appear to lie in eternal shadow.

If they never see the sun, scientists say, the craters may stay cold enough to hold ice delivered there eons ago by crashing comets.

If further studies confirm the presence of water in the craters, it would be the first found on the moon. Such lunar ice could one day be mined to supply bases with water or split into hydrogen and oxygen gas to make rocket fuel.

"Don't imagine it as pure cube ice you could put into your martini," said Eugene Shoemaker of the Lowell Observatory in Flagstaff, Ariz. "It's very dirty ice, but it's cold enough." At more than 400 degrees below zero, maybe too cold.

Clementine was launched into a lunar orbit Jan. 25. A computer malfunction on May 7 canceled plans to send it to photograph an asteroid on Aug. 31. But scientists say the spacecraft -- relatively cheap at $75 million -- has accomplished 99 percent of its scientific mission.

Among other Clementine discoveries described yesterday at the American Geophysical Union meeting in Baltimore:

* The deepest impact crater ever found in the solar system, a 7.5-mile-deep basin 1,500 miles across. Called the South Polar Aiken basin and located near the moon's south pole, it was punched into the moon's surface 4.5 billion years ago by an object 155 miles across.

* Extremes of high and low altitude on the moon twice as great as previously believed. Scientists have found a span of more than 12 miles from the highest and lowest spots. That's about the same difference seen between Earth's deep ocean trenches and highest mountains.

"It turns out the moon is a much lumpier planet than we expected it to be," said Johns Hopkins University geophysicist Maria T. Zuber.

The apparent perpetual shadows on the moon's south pole were discovered after photographs of the pole were animated.

Dr. Shoemaker said Clementine's polar orbit allowed it to take repeated photographs of the polar region during two full rotations of the moon. That allowed the photographs to show the craters illuminated from all directions.

Because the sun's angle at the pole is so low, however, the bottoms of the polar craters appear to remain in the shadows of the surrounding mountains throughout the lunar day.

No water has ever been found on the moon, and any that once existed in the open there has long-since evaporated into space.

But scientists have said since the 1960s that any water molecules that reached the moon from cometary impacts might stick to the surface if they landed somewhere that was always shaded from the sun.

During its two months in orbit around the moon, Clementine gathered more than 2 million images of the lunar surface. The images have already begun to reveal details of the moon's mineral composition and geological history.

Clementine has produced the first reliable topographic map of the moon, showing its surface contours in a multicolored map that is accurate to within 330 feet.

A companion map showing where the moon's gravitation pull is strongest will help scientists figure out the moon's interior structures, providing clues to how it was formed and evolved.

Stewart Nozette of the Ballistic Missile Defense Organization said Clementine was designed to test new, lightweight satellite systems under development for the Strategic Defense Initiative, or "star wars" program.

Guidance and tracking devices on the spacecraft may eventually be used to guide anti-missile defense rockets to their targets. But, for this mission, the Defense Department decided to have the spacecraft find, track and find its way to the moon and a near-Earth asteroid.

Planners then invited NASA to ride along, to devise scientific experiments that could take advantage of the spacecraft's cameras and sensors to study the moon. If the state-of-the-art technologies work, they will also be made available for commercial and scientific applications.

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