Lunar Splashdown

Three different spacecraft have independently detected the presence of water on the moon. And tomorrow morning, a fourth will attempt to make a big splash.

The Moon was thought to be a dry, barren place after the days of Apollo when astronauts returned, mission after mission, with samples of powdered lunar soil and rocks. The latest results from India's Chandrayaan-1 lunar probe indicate that the Moon is still a dry, barren place, but with a little bit of water hiding in the mix. And when I say a little bit of water, I really mean a tiny, minute, miniscule bit. If you could compile a ton of lunar soil, you would only amass about 32 ounces of water. However, that's still a nontrivial amount.

So how do we know this? As astronomers observing objects at such great distances, the only physical thing we have to measure is light. Lucky for us, we can learn a heck of a lot from light. One of the scientific instruments aboard Chandrayaan-1 was a spectrometer. Astronomers rely on spectrometers to detect the distribution of wavelengths of light coming from an object, in this case the Moon. While the Moon doesn't produce its own light, it reflects the sunlight that hits it in a way that is specific to its composition, i.e. the molecules that make up the lunar surface either scatter incoming sunlight or selectively absorb and/or re-radiate it. Thanks to laboratories here on Earth, we've gotten very good at identifying the exact wavelengths associated with known molecules. The spectra captured by Chandrayaan-1 show signs of absorption features that we associate with the presence of water.


But that's just scratching the surface. The next question is whether or not there is more water hidden deeper, underneath the Moon's dusty veneer.

That's where NASA comes in. Tomorrow morning at approximately 7:30am EDT, the used upper stage of a Centaur rocket that propelled the LCROSS (Lunar CRater Observing and Sensing Satellite) spacecraft to the Moon over the last three and a half months will crash into a pre-existing crater at the South Pole of the Moon. Why you ask? To create a large enough impact that the ejected material will come from not only the lunar surface, but from previously unexposed layers many meters below. The LCROSS spacecraft has a spectrometer of its own that will study the resulting plume of lunar debris and search for that telltale signature of water.