Your moon base here? Sun-washed crater rim has big vistas, but little water.

A team using observations from a lunar orbiter studied 'the living daylights' out of the Shackleton Crater, near the moon's South Pole. Their findings suggest scant water would be available to supply a lunar base there.

By Pete Spotts / June 20, 2012

De Gerlache Crater, Shackleton Crater, Sverdrup Crater, Shoemaker Crater, Faustini Crater, Cabeus Crater, and Nobile Crater, as imaged by NASA

Courtesy NASA/JPL-Caltech

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If you want to set up a base on the moon, and if plenty of local water-ice is a must, you may want to scratch Shackleton Crater from the list of possible locations.

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That is the implication of a new study based on observations from NASA's Lunar Reconnaissance Orbiter (LRO).

As a site for a lunar base, the rim of Shackleton has a lot going for it. Positioned at the moon's South Pole and just off center of the moon's slightly tilted axis of rotation, the crater's rim receives sunlight for virtually an entire lunar "day," 27.32 Earth days.

That's important for minimizing exposure to the frigid temperatures of the moon's nearly 14-day "night" at lower latitudes ? think 243 degrees below zero Fahrenheit. The sunlight also provides a near-continuous source of energy to power a moon base. Indeed, some researchers have proposed building a large infrared telescope ? best served chilled ? on the crater's shadowed floor and powering it with solar arrays on the rim.

For its part, water is desirable not only for human survival, but also as a source of hydrogen and oxygen for rocket fuel. Observations over the past 15 years, however, have proved inconclusive regarding the presence of water ice at Shackleton.

The latest LRO data indicate "that water is not there ... in a way that would facilitate human exploration," says planetary scientist Maria Zuber, who led the team analyzing the data.

If the signatures the team saw in the soils on the crater floor do indicate water, how much water might there be? Roughly 100 gallons ? enough to fill two or three residential rain barrels ? spread over a surface of about 133 square miles. Leave the swim-suit at home.

"This is not like Mars," says Dr. Zuber, a professor at the Massachusetts Institute of Technology in Cambridge, in an interview. On the red planet, explorers would find thick layers of icy soil in many locations just by turning over a shovelful or two of topsoil.

Using the lunar orbiter's laser altimeter, which measures the intensity of laser light reflected from the surface as well as the topography of the surface, Zuber?s team found that what some had interpreted as evidence for possible water-ice deposits is far more likely to signal mere rock and soil.

And while water ice remains a possible explanation for evidence seen in the soil on the crater floor, at best it would make up only about 22 percent of the top few hundred-thousandths of an inch of the soil. Data from the LRO's radar yielded no evidence of thick near-surface ice layers, which the device is capable of detecting.

Useful quantities of water or no, Shackleton is a remarkable feature in its own right. Estimated at about 3.6 billion to 3.7 billion years old, the ding in the moon's crust is 13 miles in diameter and 2.6 miles deep. It sits in a broader depression known as the South Pole-Aitken Basin ? a region of keen interest to planetary scientists working to understand how such a feature could form and what its effect is on the structure of the moon's interior.

Hints that Shackleton, as well as other polar craters, might harbor water ice first emerged in 1998, when an instrument aboard NASA's Lunar Prospector mission detected signatures from the surface indicating higher-than-expected levels of hydrogen in polar regions, including in Shackleton Crater.

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