MOON Spells "Water"

Map of Moon water; blue indicates higher concentrations of detected water molecules. Credit: NASA/Moon Mineralogy Mapper instrument.Here it comes! A veritable tidal wave of discovery on Earth's Moon….

In one short week, NASA's LCROSS (Lunar Crater Observation and Sensing Satellite) mission will quite literally come to an end—a fiery, spectacular end as it deliberately crashes into the lunar South Pole crater Cabeus A in hopes of kicking up enough material for us to detect the presence of water. If you want to see the action as it happens, come up to Chabot Space & Science Center on Friday morning, October 9, 3:00 AM to watch NASA's live simulcast and--weather and the gods of astronomy permitting--the view through Chabot's 36-inch telescope, "Nellie."

In recent months, NASA has been sending a lot of acronyms—excuse me: spacecraft—to the Moon: LRO with it's LROC, LEND, and LOLA instruments; LCROSS (which I've heard some call "LaCROSS," for the record) with its VIS, NIR, MIR, TLP, VSP, NSP—oh, the list goes on!

The fact of the matter is MOON spells "Moon." Whether or not we do end up returning humans to the Moon in the next decade, which is partly what reconnaissance by LRO and LCROSS and their arrays of acro-instrumentation is for, there are still things to be learned about our nearest neighbor in space—and water is the word at present.

Even as LCROSS and its Centaur-booster-rocket-turned-lunar-clobbering-device follow their final fatal trajectory toward Cabeus A, its launch buddy LRO, now in an orbit around the Moon and beginning to send back scientific results and images, may have already detected telltale signs of the wet stuff—which on the Moon won't be wet, but frozen solid, of course; liquid water cannot persist in the Moon's airless environment.

LRO's LEND (Lunar Exploration Neutron Detector) instrument is designed to find signs of water molecules by measuring neutron radiation emanating from the lunar surface. The Moon is constantly bombarded by high energy cosmic radiation, which forms radioactive isotopes in the soil that in turn emit neutrons. By measuring the abundance and speed distribution of the neutrons, details of soil chemistry can be inferred. The presence of light atomic nuclei--in particular the lightest of all, hydrogen, a component of water—in the soil reduces the levels of neutron emission. That drop in neutron radiation is the telltale scientists are looking for.

While LRO scientists want to make further measurements before concluding the presence water ice concentrations, observations from three other spacecraft—NASA's M3 instrument (Moon Mineralogy Mapper) aboard India's Chandrayaan-1 spacecraft and the Cassini and EPOXI spacecraft—have mutually confirmed the presence of water and hydroxyl molecules (hydroxyl is a water molecule missing one of its two hydrogen atoms) in the soils of the Moon, across much wider expanses than the confines of dark polar crater floors.

Cassini and EPOXI made measurements as they flew past the Moon to their respective destinations (Saturn, and a comet), and measurements have been made by M3 from lunar orbit. The detection of water by these spacecraft doesn't mean seas of liquid or glaciers of ice, or even blanketing layers of gaseous water vapor, but rather relatively small amounts of water and hydroxyl molecules attached to, or "stuck to," other materials in the top few millimeters of soil.

This thin "confetti" of water molecules appears to come and go with lunar daytime, forming during the cold, dark two-week-long lunar night and diminishing under the baking light of the Sun.

So, right now, MOON spells water (M3 et al), water (LRO), and possibly more water (LCROSS, on October 9th)—at least, the evidence seems to be mounting!

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