Laboratory spectroscopic detection of hydration in pristine lunar regolith

•Pristine Apollo samples contain ∼0.08-0.16 wt.% H2O+OH native to the lunar surface.•Pristine Apollo sample spectra are similar to lunar spectra acquired by spacecraft.•H2O+OH concentrations are comparable to those derived from spacecraft measurements.

Reflectance spectroscopy of Apollo lunar soil samples curated in an air- and water-free, sealed environment since recovery and return to Earth has been carried out under water-, oxygen-, CO2- and organic-controlled conditions. Spectra of these pristine samples contain features near 3 μm wavelength similar to those observed from the lunar surface by the Chandrayaan-1 Moon Mineralogy Mapper (M3), Cassini Visual and Infrared Mapping Spectrometer (VIMS), and Deep Impact Extrasolar Planet Observation and Deep Impact Extended Investigation (EPOXI) High-Resolution Instrument (HRI) instruments. Spectral feature characteristics and inferred OH/H2O concentrations are within the range of those observed by spacecraft instruments. These findings confirm that the 3 μm feature from the lunar surface results from the presence of hydration in the form of bound OH and H2O. Implantation of solar wind H+ appears to be the most plausible formation mechanism for most of the observed lunar OH and H2O.