Скачать или смотреть A Tale of Lunar Water

Presented by Casey Honniball, GSFC

For decades the lunar surface was believed to be anhydrous, however, reports by three independent spacecraft in 2009 changed this view when they detected a 3 µm hydration band on the Moon. The 3 µm absorption band is attributed to hydroxyl (OH) and possibly molecular water (H2O). The band exhibits variations with lunar time of day, temperature, soil maturity, and composition that has been interpreted as variations in water concentrations. Data from an infrared spectrometer, the Moon Mineralogy Mapper (M3) onboard the Chandrayaan-1 spacecraft, is widely used to study the 3 µm band, its spectral range, however, only covers half the hydration band. Due to the limited wavelength range of M3, variations of hydration has been called into question. To investigate the validity of variations in the 3 µm band we used the Spex infrared cross-dispersed spectrograph at the NASA InfraRed Telescope Facility (IRTF) at Maunakea Observatory in Hawaiʻi. Our improved data showed that the variation in hydration is real. But is hydroxyl or water responsible for the variations? Distinction between OH and H2O from spacecraft measurements at 3 µm is difficult due to their similar spectral properties. We have developed a new approach for unambiguous detection of the water molecule on the sunlit lunar surface. At 6.07 µm the fundamental H-O-H bend of H2O is exhibited and is strictly due to H2O without contribution by OH. The only current observatory capable of 6 µm observations of the Moon at 6 µm is the Stratospheric Observatory For Infrared Astronomy (SOFIA). Using data from SOFIA we report the first direct detection of the water molecule on the sunlit lunar surface.