Astronomers have detected water on the Moon. While that statement might sound all too familiar in recent years, previous reports were based on spectral signatures that could have been other related compounds – this time, the detection is unambiguously water, in the molecular form we need.
In 2009, NASA announced that three separate spacecraft had detected what looked like water on the surface of the Moon. The observations were done by bouncing light beams off the surface and studying how it reflected back – measuring which wavelengths of light were absorbed can reveal much about the composition of the lunar dust, or regolith.
Using this method the spacecraft detected, at wavelengths of three micrometers, the spectral signature of hydrogen and oxygen molecules. The most famous of these of course is water, containing two hydrogen atoms bound to an oxygen atom (H2O), but it’s not the only one. The absorption pattern was also consistent with related hydroxyl compounds, containing one hydrogen and one oxygen atom.
But in a pair of new studies, researchers have been able to definitively say that molecular water is present on the Moon. The Stratospheric Observatory for Infrared Astronomy (SOFIA), a telescope that operates from a 747 plane, observed the lunar surface at a longer wavelength of six micrometers and detected a spectral signature that can only be explained by H2O – that wavelength is not shared by any other hydroxyl compounds.