Dec
07
2009

The moon reveals its secrets

LCROSS: Centaur rocket separating from the shepherding spacecraft upon final approach of the moon.
LCROSS: Centaur rocket separating from the shepherding spacecraft upon final approach of the moon.Courtesy NASA
On June 18, 2009, NASA sent up the Lunar CRater Observation and Sensing Satellite (or LCROSS, as it’s called) with the intent to find water on the moon. How? By sending LCROSS on a kamikaze mission. The first component of LCROSS (the Centaur rocket) smashed into the moon at speeds faster than a bullet. The second component (the shepherding spacecraft) then flew through the resulting cloud, gathered the vaporized particles, analyzed them, and sent that data back to Earth before it, too, crashed into the lunar surface. Although most earthling telescopes were unable to see the plume, as NASA had predicted (Joe mentioned this in his post just after the impact), it was large enough (10-12 km across) to get the information they were looking for.

What did they find? Oh, only that there’s water on the moon! How, exactly, did scientists come to this conclusion? The target for impact of LCROSS was located deep in the Cabeus crater on the moon’s south pole. This region is permanently in shadows and very cold. When the plume of debris rose above the crater’s rim and was exposed to sunlight, any water-ice, hydrocarbons, or organics vaporized and broke down into their basic components. Those components are what the spectrometers in the shepherding spacecraft picked up, analyzed, and sent back to earth. What’s interesting is that there were two independent spectrometers on board: an ultraviolet visible spectrometer and a near infrared spectrometer, and both relayed the presence of water.

Spectrometers produce graphs that look like EKG’s after a ton of caffeine. In the case of the NIR spectrometer, scientists compared the shape (spectral signature) of the graph sent back from LCROSS to those of various known materials. The LCROSS spectral signature matched that of water. For the ultraviolet visible spectrometer, however, scientists found the specific spectral signature spike (say that ten times fast) indicative of hydroxyl. Hydroxyl is produced when water vapor is broken up by sunlight, which is exactly what happened when the moon dust escaped the crater. Having two instruments saying the same thing makes scientists more confident that there is, indeed, water on the moon.

So, there’s water on the moon. Why is that a big deal? One reason involves future space exploration. Launching rockets directly from the moon for exploration in other parts of the solar system is much easier (due to the gravity being 1/6th that on Earth) and more cost effective (you can use smaller rockets) than launching from Earth. In order to do this efficiently, though, we would need to produce rocket fuel on the moon: hydrogen (the “H” in “H2O,” just to belabor a point) is required for this. Having a local supply of water is also important in establishing local infrastructure: semi-permanent lunar settlements, perhaps. Exploration aside, simply learning as much as we can about our nearest neighbor helps us continue to piece together this solar system we call home.

See the full LCROSS briefing here.

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