Thursday, September 24, 2009

Confirming a damp Moon

The lunar surface as swept up by Cassini during its accelerating fly-by returning through the Earth-Moon system on the way to Saturn in 1999 showed regions of trace surface water (blue) and hydroxyl (orange and green) in daylight and at equatorial latitudes. [Science] On Aug. 19, 1999 the observations show water and hydroxyl at all latitudes on the surface, even areas exposed to direct sunlight. The Visual and Infrared Mapping Spectrometer (VIMS) view was slightly south of the lunar equator. The yellow cross indicates a latitude and longitude of zero. The picture at top left shows infrared light reflected off the moon as seen by VIMS. The top right picture shows the moon as seen by Cassini's Imaging Science Sub-system (ISS) during the flyby. The image at bottom left shows temperatures of the moon derived from VIMS data. Temperatures near the equator are hotter than boiling water on Earth. The bottom center picture shows a VIMS map of water associated with minerals. At bottom right is a VIMS map of hydroxyl-bearing minerals, created by chemical reactions with minerals and glasses in the lunar soil. [NASA/JPL-Caltech/USGS]

Kenneth Chang
New York Times

There appears to be, to the surprise of planetary scientists, water, water everywhere on the Moon, although how many drops future astronauts might be able to drink is not clear.

Data from three spacecraft indicate the widespread presence of water or hydroxyl, a molecule consisting of one hydrogen atom and one oxygen atom as opposed to the two hydrogen and one oxygen atoms that make up a water molecule. The discoveries are being published Thursday on the Web site of the journal Science.

“It’s so startling because it’s so pervasive,” said Lawrence A. Taylor of the University of Tennessee, Knoxville, a co-author of one of the papers that analyzed data from a National Aeronautics and Space Administration instrument aboard India’s Chandrayyan-1 satellite. “It’s like somebody painted the globe.”

For decades, the Moon has been regarded as a completely dry place. The dark side is more than ice cold, but when it passes into sunlight, any ice should have long ago been baked away. The possible exceptions are permanently shadowed craters near the Moon’s poles, and data announced this month by NASA verified the presence of hydrogen in those areas, which would most likely be in the form of water.

If water is somehow more widespread, that could make future settlement of the Moon easier, especially if significant water could be extracted just by heating the soil. Oxygen would also be a key component for breathable air for astronauts, and hydrogen and oxygen can also be used for rocket fuel or power generation.

Samples of lunar soil brought back from NASA’s Apollo missions about four decades ago actually did show signs of water, but most scientists working with the samples, including Dr. Taylor, dismissed the readings as contamination from humid Houston air that seeped in before the rocks were analyzed at NASA’s Johnson Space Center.

“I was one of the ones back in the Apollo days that was firmly against lunar water,” Dr. Taylor said.

Now he is convinced he was wrong. “I’ve eaten my shorts,” he said.

The Chandrayyan-1 data looked at sunlight reflected off the Moon’s surface and found a dip at a wavelength where water and hydroxyl absorb infrared light. Dr. Taylor estimated the concentration at about one quart of water per cubic yard of lunar soil and rock.

Meanwhile, Roger N. Clark of the United States Geological Survey analyzed decade-old data from NASA’s Cassini spacecraft when it passed the Moon en route to Saturn. He, too, found signs of water or hydroxyl, mostly at the poles, but also at lower latitudes.

Scientists working with the Deep Impact spacecraft, which later studied the Comet Tempel 1, also found infrared absorption at the water and hydroxyl wavelengths. More interesting, the amount of absorption — and thus the quantity of water — varied over time.

That suggests the water is being created when protons from the solar wind slam into the lunar surface. The collisions may free oxygen atoms in the minerals and allow them to recombine with protons and electrons to form water.

Lori M. Feaga, a research scientist at the University of Maryland who is a member of the team that analyzed the Deep Impact data, said this process would work only to about one millimeter into the lunar surface. If correct, that would not give future astronauts much to drink.

“You would have to scrape the area of a baseball field or a football field to get one quart of water,” she said.

Data from three spacecraft indicate that a thin film of water coats the surface of the soil in at least some spots, a discovery that raises the possibility of colonization.

John Johnson, Jr.
Los Angeles Times

Space scientists have found the strongest evidence yet that water exists on the moon, a discovery that helps complete a picture of a water-rich solar system and that could make colonizing our nearest neighbor in space much easier than previously thought.

Using data from three spacecraft that have made close flybys of the moon in recent years, research teams in the United States have found proof that a thin film of water coats the surface of the soil in at least some places on the moon.

"Within the context of lunar science, this is a major discovery," said Paul G. Lucey, a planetary scientist with the University of Hawaii, who was not involved in the current research. "There was zero accepted evidence that there was any water at the lunar surface, [but] now it is shown to be easily detectable, though by extremely sensitive methods. As a lunar scientist, when I read about this I was completely blown away."

The discovery "will forever change how we look at the moon," added Roger Clark, a scientist with the U.S. Geological Survey in Denver and the author of one of three papers -- each dealing with data from a different spacecraft -- appearing in this week's edition of Science magazine.

For decades, the moon had been considered a dead and uninteresting world by scientists. The Apollo missions of the 1960s and '70s brought back some rocks that contained tiny amounts of trapped water, but scientists at the time decided they had been contaminated by water from Earth.

Proponents of human space travel hope this new discovery could put pressure on the White House to follow through with the Bush administration's plans to return to the moon by 2020 and to construct Earth's first off-world colony there.

At the very least, the discovery lends weight to a new view of a friendlier solar system, where water, the lifeblood of biology on Earth, suddenly seems to be everywhere. Last year's Phoenix mission to Mars' polar region found ice just beneath its struts. Ice has been found on Saturn's moon Titan and it covers Jupiter's moon Europa.

Research teams from Brown University, the University of Maryland and the U.S. Geological Survey used spectroscopic measurements taken of the lunar surface by NASA's Cassini and Deep Impact spacecraft, as well as India's Chandrayaan 1 satellite. The instruments on all three spacecraft detected the signature of the OH chemical bond (oxygen and hydrogen) at many places on the lunar surface, including areas subject to daytime temperatures that reach the boiling point of water. The greatest concentrations were found in the coldest regions, however, near the two poles.

Detecting the OH bond is not a sure indicator of water. The instruments could be picking up hydroxyl, which is composed of one oxygen and one hydrogen atom. Water has two hydrogen atoms and one oxygen.

But one of the papers, by research scientists Lori Feaga and Jessica Sunshine of the University of Maryland, found clear evidence for both hydroxyl and water in measurements taken by the Deep Impact spectrometer on June 2 and June 9. "We saw both species," Feaga said.

The amount of water in any one place is tiny. Clark estimated it at about a quart per ton of soil.

The moon "is almost as wet as a bone," Lucey said in an e-mail interview with The Times. "It is in the form of an imperceptible film on soil grains, perhaps several molecules thick."

Unless science makes some technological breakthrough, it would be extremely difficult for future moon colonists to harvest such tiny amounts of water. The research indicates, however, that the water migrates toward the poles -- by literally lifting off the soil particles and drifting north and south -- when the temperature rises during the lunar day. When the water molecules land in a colder area near the poles, they are trapped there in higher concentrations, "perhaps high enough to use," Lucey said.

The question of how much water might have accumulated at the poles could be answered on Oct. 9, when NASA's Lunar Crater Observation and Sensing Satellite, known as LCROSS, is set to steer a rocket into a south pole crater called Cabeus A. The resulting collision, which will send up a dust cloud two miles above the surface of the moon, will be observed and sampled by satellites and observatories on Earth for evidence of water. Cabeus A was chosen because it is in a perpetual shadow, so any water stored there in the form of ice would not melt.

"The results of the present studies lend credence to the lunar polar water hypothesis by providing a proven source of water on the surface of the moon," Lucey said.

If there is water on the moon, where did it come from? One possibility, according to the research teams, is that the water was deposited by one or more comets colliding with the moon. Another is that meteorites colliding with the moon might have unearthed underground sources of water.

Finally, the solar wind, a stream of charged particles flowing outward from the sun, which is mostly made up of hydrogen and helium, could play a role. The solar wind could supply hydrogen to bind with oxygen in lunar soils.

Perhaps ironically, given how many spacecraft have orbited and landed on the moon in the last five decades, two of the spacecraft that made this discovery had other missions besides observing the moon. Cassini's primary mission was to observe Saturn and its major moons, including the bizarre smog-choked Titan. The measurements of the moon were taken in 1999 as Cassini was on its way to Saturn.

Deep Impact shot a rocket into the comet Tempel 1 in 2005 to find out what a comet is made of, but has since been given other jobs, including rendezvousing with another comet. Chandrayaan 1, India's first moon-orbiting satellite, was launched in October 2008.

All three spacecraft carried spectrometers, which operate by breaking down the light reflected off the surface of the moon. Because every chemical molecule has a different light wavelength signature, scientists analyzing the spectrograph can tell what the surface is made of. The reason the Deep Impact instrument was able to see both water and hydroxyl, Feaga said, was because it has a larger bandwidth than the instruments carried by Cassini and Chandrayaan.

"It is astounding to find water at all latitudes on the moon and in places where the temperature is hotter than boiling water on Earth," Clark said.

The discovery comes at a pivotal time for America's space program. Former President George W. Bush set NASA on an ambitious course to return to the moon by 2020 and then travel on to Mars. But a presidential commission recently found that without a significant increase in its budget, NASA won't be able to reach either goal.

It's unclear how this new discovery will affect the debate in Washington over NASA's future, but the presence of water on the moon would presumably make colonization much easier. Water would not only be valuable for drinking, but it could also be used to make oxygen for breathing and to make rocket fuel for trips to and from Earth.

"Perhaps the most valuable result of these new observations is that they prompt a critical reexamination of the notion that the moon is dry," Lucey said. "It is not."

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