Since the surprise discovery last year of trace amounts of water on the moon, scientists have been redefining their concept of Earth's rocky neighbor. Now researchers say the water on the moon comes in three different flavors.
Until recently the moon was thought to be bone dry. But measurements in the last year from the Mini-SAR and Moon Mineralogy Mapper (M3 or "M-cubed") instruments on India's Chandrayaan-1 moon probe and from NASA's recent LCROSS mission have proved that wrong.
Mini-SAR found 40 craters, each containing frozen water at least 6.6 feet deep on the lunar surface – which adds up to 600 million tons of lunar ice stuff altogether. LCROSS slammed into the moon on Oct. 9, 2009 and found evidence of water in another crater.
"So far we've found three types of moon water," said Paul Spudis of the Lunar and Planetary Institute in Houston, Texas. "We have Mini-SAR's thick lenses of nearly pure crater ice, LCROSS's fluffy mix of ice crystals and dirt, and M-cube's thin layer that comes and goes all across the surface of the moon."
LCROSS struck moon water in a cold, permanently dark crater at the lunar south pole. Since then, the science team has been thoroughly mining the data collected from the intentional moon crash.
"It looks as though at least two different layers of our crater soil contain water, and they represent two different time epochs," said Anthony Colaprete, LCROSS principal investigator. "The first layer, ejected in the first 2 seconds from the crater after impact, contains water and hydroxyl bound up in the minerals, and even tiny pieces of pure ice mixed in. This layer is a thin film and may be relatively 'fresh,' perhaps recently replenished."
This brand of moon water resembles the water M3 discovered last year in scant but widespread amounts, bound to the rocks and dust in the very top millimeters of lunar soil, scientists say. But the second layer is different.
"It contains even more water ice plus a treasure chest of other compounds we weren't even looking for," he says. "So far the tally includes sulfur dioxide (SO2), methanol (CH3OH), and the curious organic molecule diacetylene (H2C4). This layer seems to extend below at least 0.5 meters and is probably older than the ice we're finding on the surface."
The researchers don't yet know why some craters contain loads of pure ice while others are dominated by an ice-soil mixture. It's probably a sign that the moon water comes from more than one source.
"Some of the water may be made right there on the moon," Spudis said. "Protons in the solar wind can make small amounts of water continuously on the lunar surface by interacting with metal oxides in the rocks. But some of the water is probably deposited on the moon from other places in the solar system."
These findings are completely rewriting the book on the moon.
"It's a different world up there," says Spudis, "and we've barely scratched the surface. Who knows what discoveries lie ahead?"