Thursday, October 21, 2010

Moon Not Only Has Water, but Lots of It

Scientists have discovered significant amounts of water on the moon—about twice the quantity seen in the Sahara Desert—a finding that may bolster the case for establishing a manned base on the lunar surface.

In an audacious experiment last year, the National Aeronautics and Space Administration slammed a spent-fuel rocket into a lunar crater at 5,600 miles an hour, and then used a pair of orbiting satellites to analyze the debris thrown off by the impact. They discovered that the crater contained water in the form of ice, plus a host of other resources, including hydrogen, ammonia, methane, mercury, sodium and silver.

Jack Pfaller/NASA

NASA's Lunar Crater Observation and Sensing Satellite and its Centaur booster rocket crashes into the moon in this artist's illustration.

NASA announced its groundbreaking discovery of lunar water last October. Now, a more detailed analysis of the data—the subject of six research papers being published Friday in the journal Science—concludes that there is a lot more water on the moon than anyone expected.

"It's really wet," said Anthony Colaprete, co-author of one of the Science papers and a space scientist at NASA Ames Research Center at Moffett Field, Calif. He and his colleagues estimate that 5.6% of the total mass of the targeted lunar crater's soil consists of water ice. In other words, 2,200 pounds of moon dirt would yield a dozen gallons of water.

The presence of so much water strengthens the argument for establishing a manned lunar base from which to launch other interplanetary adventures. Water is crucial because its components, hydrogen and oxygen, are key ingredients for rocket fuel.

Having a source of water on the moon is critical because the cost of transporting a large amount from earth would be prohibitive. On the moon, a bottle of water would run about $50,000, according to NASA, because that is what it costs, per

The U.S. likely won't be involved in manned voyages to the moon anytime soon. President Barack Obama recently canceled a NASA program to return astronauts to the lunar surface a decade from now. The agency, however, is working on the grander, longer-term prize of a manned trip to Mars.

But other countries are gearing up. China has pledged to land astronauts on the moon by 2025 and India by 2020. Japan wants to establish an unmanned moon base in a decade, potentially setting the stage for a manned mission later. Only the U.S. has sent astronauts to the moon thus far.

Cabeus is a cosmic trap. Any material from space landing there tends to stick. "There's almost no energy to warm up the molecules, so that they can't bounce off again," said G. Randall Gladstone, co-author of one of the Science papers and a planetary scientist at the nonprofit Southwest Research Institute in San Antonio.

Dr. Gladstone and others believe that Cabeus contains cosmic material that has accumulated over a billion years or more.

Scientists know that most of the moon is drier than the driest terrestrial desert. And while remote observations had suggested that water ice might be present at cold-trap regions of the moon, there was no direct evidence.

To settle the debate, NASA devised a clever plan and set it in motion on June 18, 2009, with the launch of a rocket from Cape Canaveral, Fla. The rocket was stacked with an upper-stage rocket known as Centaur. Above it, sat the Lunar Crater Observation and Sensing Satellite, or LCROSS, roughly the size of a Volkswagen Bug. Atop that sat another satellite, the Lunar Reconnaissance Orbiter, or LRO.

Soon after lift off, LRO separated and headed for the moon. So did the still-joined LCROSS and Centaur modules, but via a different route. On Oct. 9, the Centaur sped off on its own—aimed for Cabeus and trailed by a hurtling LCROSS.

Drained of fuel, Centaur was now the equivalent of an empty soda can that was 36 feet tall. When it slammed into the crater, it blew a hole some 75 feet wide. It also spewed at least 8,800 pounds of debris, dust and vapor into LCROSS's sunlit field of view. LCROSS by then was 373 miles above the lunar surface. Its instruments began collecting data about the quantity of water vapor and ice in the plume, then zapping it to receiving stations on earth. Four minutes later, LCROSS smashed into the lunar ground as well, becoming dirt.

The LRO satellite, meanwhile, orbited 31 miles above the moon. Its main task—which it continues to do today—was to create a three-dimensional map of the moon's surface. But it also collected data on the impact plume. One instrument aboard the LRO was an ultraviolet spectrograph that can detect various gases and substances. Many of the findings were unexpected.

About 20% of the Cabeus dirt is a mix of different elements and volatile compounds, including water. "That was a real surprise. I don't think anyone appreciated that it would be as much as 20%," said Dr. Colaprete. A lot of the remaining dirt is made from the typical components of moon rock, including feldspar and basalt.

The scientists also found molecular hydrogen in the soil. "That's interesting because if you want to make rocket fuel you could heat up the soil and hydrogen would come pouring out," said Dr. Gladstone.

In 1999, American scientist George W. Reed published a study arguing that lunar cold traps would likely contain significant amounts of mercury, which is toxic to humans. The paper was titled "Don't drink the water."

He was right: LRO's instruments detected sizable quantities of mercury—about 1%—in the lunar soil.

Researchers were also surprised to find compounds such as hydrogen sulphide, which are the result of a chemical reaction. But how could any reactions occur in such a cold place? Dr. Colaprete speculates that solar winds and cosmic rays may be providing minute amounts of energy, allowing such reactions to take place over hundreds of millions of years.

Is that also how the water got there? "No, that approach would only create small amounts of it," said Dr. Colaprete. "It suggests to me that water and some of the other elements were brought in by a comet. Cabeus is an old comet site."

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