Lunar Oasis

A QUANTUM OF SCIENCE

Three separate space probes find spectral evidence of lunar water

In October 2008, India launched the Chandrayaan-1, its first lunar probe. The Chandrayaan-1 was designed to spend the following two years mapping the surface of the moon, but on August 31, 2009 contact with the probe was lost. Before then, however, the probe generated over 70,000 high-resolution images covering almost the entirety of the moon’s surface. Even more importantly, its sensors revealed a curious observation: ice.

Light absorbance is the characteristic interaction of different wavelengths of light with particular chemical elements. If a specific element is present in a material, it will absorb light of a characteristic wavelength. The same is true for simple compounds, such as water. With this technique, specific elements and often simple compounds can be detected even at interstellar distances, allowing scientists to deduce the chemical composition of distant stars. One compound that has a particularly characteristic absorbance spectrum is water. The Chandrayaan’s sensors reported a spectrum containing absorbance peaks consistent with water, and soon afterwards the observations were repeated by NASA’s Cassini and Deep Impact space probes.

Isn’t the moon a dry desert, though? Apollo astronauts certainly believed so when they landed on the moon in 1969, and "moon rocks" brought back from the lunar landing seemed to confirm it – except that it was assumed that any humidity found in the samples were the result of earth water contamination. Now, scientists theorize that water exists on the lunar surface in extremely thin layers just millimeters below the surface. The source and amount of water are still matters for further investigation, but scientists theorize that water on the surface of the moon might "migrate" as the moon is alternately warmed and cooled by exposure to the sun, until it ends up in deep lunar craters. These craters were recently found to be at a lower temperature than the surface of Pluto, so water ending up there would be "stuck" and accumulate over time.

The existence of water on the moon is particularly exciting not only because it was contrary to decades-old assumptions but also because it creates new possibilities. If it could be effectively harvested, lunar water could help sustain a human outpost on the lunar surface. Even more daringly, some have suggested that hydrogen and oxygen derived from electrochemically "splitting" this water could serve as rocket fuel. Rockets launched from the moon would require substantially less fuel because the moon’s gravity is so much less than that on Earth, leading to speculation that lunar launches could facilitate a new era in the exploration of the solar system, especially Mars.

For more information:

India's first lunar probe fails after less than a year (New Scientist)

Widespread water may cling to moon's surface (New Scientist)

How astronauts could 'harvest' water on the moon (New Scientist)

What Do Spectra Tell Us? (NASA)


© AQOS / P. Smalley (2009)
Reproduction with attribution is appreciation