ISRO-SAC instrument finds presence of hydroxyl and water molecules on Moon

In a pathbreaking discovery, ISRO’s homegrown instrument aboard Chandrayan-2 has detected the unambiguous presence of hydroxyl and water molecules on the Moon with the precision of differentiating between the two.

The research also strongly suggests that the presence of these could correlate with mineralogy and latitudinal location, according to a paper published in the latest issue of fortnightly journal ‘Current Science’.

The Imaging infrared spectrometer (IIRS), an imaging instrument that collects information from the electromagnetic spectrum for understanding the mineral composition of the lunar surface with each element possessing a ‘spectral signature’ unique to itself, was developed by Ahmedabad-based unit of Space Applications Centre (SAC) of ISRO.

The discovery is being hailed as critical for future planetary exploration and resource utilisation.

While the first Moon mission of Chandrayan-1 in 2008 carried a similar instrument called Moon Mineralogy Mapper (commonly known as M3) capable of detecting water, the range of detection was lower — between 0.4 to 3 micrometre — and was also developed by NASA’s Jet Propulsion Laboratory and was not indigenous to ISRO. The higher wavelength range of IIRS permits for better accuracy in results. In September 2009, results published of the M3 instrument data had shown detection of absorption features on the polar regions of the surface of the moon “usually linked to hydroxyl- and/ or water-bearing molecules,” as NASA states. A 2017 research article by researchers from the Brown University had noted, “…the wavelength range of M3 is too limited to accurately determine the full shape and maximum absorption point within the 3-µm (micrometre) region, making it difficult to differentiate OH (hydroxyl) from H2O (water), particularly if both species are present.” Notably, the human eye is capable of detecting wavelengths in the range of 0.3 and 0.7 micrometre.

Prakash Chauhan, director at IIRS Dehradun, in response to queries by The Indian Express said in a written statement that since the spectral coverage of M3 instrument was limited upto 3 micrometre, distinction between hydroxyl, water and water ice/frost was not possible.

As more data from the mission is made available in the future, researchers are hoping that they will be able to learn more about hydroxyl and water production and hydration processes on the moon

As per a research article in the August issue of Current Science, three strips on the Moon’s surface were analysed by IIRS sensor for hydration presence and as reported, the initial analysis “demonstrates the presence of widespread lunar hydration and unambiguous detection of OH (hydroxyl) and H2O (water) signatures on the Moon.” It was also observed from the data that the rockier regions of the Moon were found to have higher hydroxyl or possibly water molecules, compared to the large basaltic plain regions where hydroxyl appeared to be dominant, especially at higher surface temperature.

As the paper, authored by scientists from IIRS-Dehradun, SAC in Ahmedabad, UR Rao Satellite Centre and ISRO headquarters in Bengaluru, notes, the most common and widespread process for the formation of hydroxyl and water on the Moon is considered to be due to interaction of solar winds with the lunar surface.