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Lunar impact mission scooped up more than water

Posted: October 21, 2010

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Astronauts exploring the moon's south pole should bring a shovel.

NASA's robotic mission to plunge an empty rocket stage into a lunar crater last year confirmed the presence of large quantities of water ice and hydrogen, but it also found traces of silver and mercury, scientists said Thursday.

Artist's concept of the LCROSS shepherding spacecraft observing the Centaur impact. Credit: Northrop Grumman
The findings are encouraging to advocates for further lunar exploration, be it with humans or robots.

"Once you make a discovery of a potential resource, the next thing you want to do is go prospecting," said Michael Wargo, the chief lunar scientist in NASA's exploration division.

The Lunar Crater Observation and Sensing Satellite, or LCROSS, crashed a spent Centaur rocket into the permanently dark Cabeus crater near the moon's south pole in October 2009. The goal: excavate thousands of tons of material and look for water.

A dedicated shepherding satellite flew right behind the Centaur, collecting in situ measurements of the dust cloud ejected by the rocket's nearly 6,000 mph impact.

Instruments aboard the Lunar Reconnaissance Orbiter, which launched with LCROSS, viewed the immediate aftermath of the rocket collision from its perch high overhead.

The results will be published Friday in Science magazine.

Speaking to reporters Thursday, scientists said they found about 50 percent more water than expected.

But there were also other surprises.

The missions found evidence of water ice in the lunar subsurface outside of the permanently-shadowed regions at the poles. Researchers expected water inside cold pockets in craters with rims that block sunlight at low angles.

"Some places that see sunlight during the year are, in fact, cold enough to preserve water ice beneath the surface," said David Paige, the principal investigator for LRO's Diviner instrument at the University of California, Los Angeles.

Diviner data show the temperature inside Cabeus was 38 Kelvin, or nearly -400 degrees Fahrenheit.

LRO's Diviner instrument collected data for this temperature map of the lunar south pole area. Credit: UCLA/NASA/JPL/Goddard
Many of the water discoveries were summarily announced last year, but scientists Thursday added more details to the picture of conditions at the lunar south pole, long a popular potential destination for future human and robotic missions.

Data analysis shows LCROSS hit a surface not like an icy skating rink, as predicted before the impact, but more akin to "fluffy, snow-covered dirt," Wargo said.

The average concentration of water in the ejecta plume in four minutes of observations was 5.6 percent, but the margin of error is 2.9 percentage points either side of that figure, according to Anthony Colaprete, LCROSS project scientist and principal investigator at NASA's Ames Research Center.

Peter Schultz, a professor of geological sciences at Brown University, said scientists found the chemical signatures of silver and mercury.

"We opened this lunar closet and discovered things we just didn't expect," Schultz said.

LRO's ultraviolet LAMP instrument also found signs of frozen carbon dioxide, carbon monoxide, and molecules of hydrogen.

"Some of the species found, for example molecular hydrogen and mercury, probably have important implications for future manned exploration and resource utilization," said Randy Gladstone, LAMP's deputy principal investigator at the Southwest Research Institute in San Antonio.

Colaprete described the Cabeus impact site as an oasis in a lunar desert. Chemical maps from a Russian neutron detector aboard LRO artifically paint Cabeus blue, a sign of significantly more water there than other regions on the moon, according to Igor Mitrofanov of the Institute for Space Research in Moscow.

"That's a significant amount of water," Colaprete said. "And it's in the form of water ice grains, at least a significant amount of it is. That's good because water ice is a friendly resource to work with."

According to Colaprete, there are 11 or 12 gallons of water for every metric ton, or 2,200 pounds, of lunar soil in Cabeus. Up to a billion gallons of water could be extracted in a region 6 miles around the impact site.

Scientists say they still need better data to chart the exact distribution of the water, including its depth in sunlit regions.

"One of the things LCROSS was meant to do was to understand the hydrogen and its potential as a resource," Colaprete said. "Based on our results, the answer is yes. The resources are there and potentially usable at a base in the future."