What's the moon made of? NASA mission finds it's nothing so simple as cheese.
Thursday, October 21, 2010; 10:46 PM
Gazing at the moon will just never be the same.
It remains a place of mystery, for sure. But scientists say they now know that the moon has enough water ice and vapor to potentially quench the thirst of lunar astronauts and even fuel lunar rockets. Plus, it has a cache of familiar compounds - organics such as methane and ammonia, some mercury and even traces of sulfur and and silver - that were found hidden away in the moon's deep shadows.
"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, get flash-frozen and collect in craters, where they stay "in the permanent shadows." The crevices and their contents are like "oases in the desert," said Anthony Colaprete, project scientist for the mission from NASA's Ames Research Center.
The impact at the Cabeus crater dug a holone-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.
Surprisingly, last year's controlled crash revealed substantially more about what the moon is made of than the Apollo missions that landed astronauts there a generation ago and brought soil and rock samples back to Earth. The Apollo spacecraft landed in the parched midlands of the moon, but last year's mission tested the south polar region, which turns out to be far more chemically diverse.
Although the presence of lunar ice and water vapor was reported from that mission, the amount of H2O present was not known until the newest papers were released.
Colaprete and his colleagues calculated that the water ice and vapor in the plume of debris were 5.6 percent of its mass, and consequently the crater's. The finding, which had a reporting error of 2.9 percentage points, describes a considerably higher concentration of H2O than expected. When the water and all other detected compounds are added together, 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.
In a teleconference Thursday, Colaprete expanded on the findings and said scientists think there are probably large areas of lunar permafrost as well, where frozen water lies under the surface.
The papers by Colaprete and Schultz were among those released Thursday by the journal Science that focus on NASA's Lunar Crater Observation and Sensing Satellite, or LCROSS. In that mission last year, a spent rocket crashed into the moon at twice the speed of a bullet, followed by a data-collecting "shepherding spacecraft" that passed through the plume of debris created by the crash. A Lunar Reconnaissance Orbiter arrived on the scene as the mayhem was playing out.
The discoveries, Schultz said, show the moon to be far more chemically complex than presumed during the Apollo era and will forever change how scientists look at the moon.
"The Apollo astronauts saw only small regions of the moon and generally were nowhere near the poles," he said. "But the poles are where all that great chemistry was hidden."
Apollo astronauts had also detected trace amounts of silver on the moon but nothing at the level found near the southern pole. Schultz said the silver 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. Scientists also said during the teleconference that there was not enough silver in the soil to give the moon its sheen. Still, the discoveries led scientists to speculate about the potential for the moon holding larger amounts of compounds that could someday be collected and maybe put to use.
The molecules found in the crash cloud had probably 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.
Water on the moon, if plentiful, could be a valuable resource for space exploration. It could provide drinking water for astronauts on lengthy missions, and 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. China and India have plans to land on the moon in the 2020s, and Japan has voiced interest in setting up an unmanned and then a manned colony.