Hidden in the moon's deep shadows are caches of frozen water, organic compounds such as methane, toxins such as mercury and even traces of silver and gold — a previously unimagined trove of lunar chemistry, scientists announced Thursday.
Hidden in the moon’s deep shadows are caches of frozen water, organic compounds such as methane, toxins such as mercury and even traces of silver and gold — a previously unimagined trove of lunar chemistry, scientists announced Thursday.
These compounds and much more were kicked up when a NASA rocket and spacecraft were crashed into the lunar south pole a year ago.
The impact at the Cabeus crater dug a hole one-third the size of a football field and as deep as a swimming pool — setting loose chemical elements that lay in some of the coldest spots in the solar system and haven’t seen sunlight for billions of years.
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“This place looks like it’s a treasure chest of elements,” said Brown University planetary geologist Peter Schultz, one of the principal investigators of the NASA mission. He said the compounds migrate to the poles and then are quick-frozen and collect in craters, where they stay “in the permanent shadows.”
Although the presence of some lunar ice and water vapor previously had been reported from that mission, the full richness of what lies in the coldest and darkest reaches of the moon took a year to tease out.
The discoveries, Schultz said, show the moon to be far more chemically complex than presumed during the Apollo era — even after decades of studying lunar rocks — and will forever change how scientists look at the moon.
Apollo astronauts also had detected trace amounts of silver on the moon but nothing on the level now found at the southern pole region. Schultz said the silver and gold molecules detected were in atomic form — loosely attached to grains of lunar soil, or “regolith” — and were not the kind of deposits that could be mined.
The broad collection of molecules found in the crash cloud probably had fallen onto the moon long ago and, in the virtually complete absence of a lunar atmosphere to keep them in place, migrated to the poles, Schultz said. Had they not been quick-frozen in the crater, they, too, would probably have flown off into space, as most incoming molecules do.
He said the molecules are most likely brought to the moon by comets, asteroids and solar winds.
Schultz was one of six investigators whose papers on the results of the moon crash-landing will be published Friday in the journal Science.
The mission, called the Lunar Crater Observation and Sensing Satellite, or LCROSS, consisted of a spent rocket that crashed into the moon at twice the speed of a bullet, the data-collecting “shepherding spacecraft” that followed the rocket and passed through the plume of debris created by the crash, and the Lunar Reconnaissance Orbiter that arrived on the scene as the lunar mayhem was playing out.
Another Science paper using LCROSS data, written by Anthony Colaprete of NASA’s Ames Research Center and colleagues, calculated that the water ice and vapor in the plume was 5.6 percent of its mass, and consequently of the crater’s.
That finding, which had a reporting error of plus or minus 2.9 percent, described a considerably higher concentration of H2O than expected. When the water and all other detected compounds are combined, the scientists said, they make up 10 to 15 percent of the mass of the crater’s soil — again, a much higher percentage than previously understood.
Colaprete’s paper describes how the satellite collected data that allowed researchers to understand the crash in detail and to estimate that 342 pounds of water vapor and water ice were ejected from the darkness of the crater into the LCROSS field of view.
Water on the moon, if plentiful enough, could be a valuable resource for space exploration. It not only could provide drinking water for astronauts on lengthy missions, but also its hydrogen and oxygen could be used to create rocket fuel. A space engineering firm in Texas, Stone Aerospace, has been developing long-term plans to do precisely that kind of water mining on the moon’s Shackleton crater.
Just as the poles have nearby crater floors with permanently shaded regions because of the moon’s orientation to the sun, they also have nearby mountains and crater rims that are in nearly perpetual sunlight. In theory, they would be perfect locations for solar-powered systems and equipment. But the LCROSS mission also found a substantial presence of mercury in the soil.
“The detection of mercury in the soil was the biggest surprise, especially that it’s in about the same abundance as the water detected by LCROSS,” said Kurt Retherford, who worked on one of the Lunar Reconnaissance Orbiter instruments. “Its toxicity could present a challenge for human exploration.”
Under the Obama administration, a proposed Bush-era effort to set up human colonies on the moon has been largely scrapped. Although plans for moon colonies and intensive exploration have been shelved for now, scientists said the LCROSS mission was a success in revealing new secrets of the moon. But the new understandings, they said, raise far more questions than they answer.
“There’s this archive of billions of years” in the moon’s permanently shadowed craters, Schultz said. “There could be clues there to our Earth’s history, our solar system, our galaxy. And it’s all just sitting there, this hidden history, just begging us to go back.”