A research team from the Space Applications Centre (SAC) of the Indian Space Research Organisation (ISRO) in Ahmedabad, led by Satadru Bhattacharya, has found evidence of water of volcanic origin — water that has originated from deep within the Moon’s interior — rather than water-bearing igneous surface lunar material detected hitherto by different lunar missions including Chandrayaan-1.
Thus far scientists had believed lunar rocks were “bone dry” and that any water detected in lunar samples was either due to contamination from the Earth or produced by solar wind and other exogenous extra-lunar sources. Significantly, the concentration of the water detected by Indian researchers — 0.55 per cent by weight — is the highest ever found on the Moon, according to Prakash Chauhan, a member of the team.
The finding is based on an analysis of high-resolution spectral data of the Compton-Belkovich Volcanic Complex (CBVC) region on the far side of the Moon obtained by the NASA instrument Moon Mineralogy Mapper (M3), which was sent aboard the Indian lunar mission Chandrayaan-1. Unlike the earlier detection of water and hydroxyl molecules in the polar region of the Moon by Chandrayaan-1 and other missions, CBVC is a non-polar region. A 2011 work on the geology of the CBVC region by B. L. Jolliff and others had found it to be highly rich in silica, which makes its geology totally different from that of the polar regions. The Indian finding has been reported in the latest on-line edition of the journal Current Science .
The Indian work comes close on the heels of a similar finding based on M3 data on the central peak of the volcanic crater Bullialdus, which was reported by R. Klima and associates in Nature Geoscience about a fortnight ago. Crater Bullialdus is in the equatorial region of the Moon and Klima and company had suggested that the water signatures observed could be of magmatic or volcanic origin as the non-polar Bullialdus crater region is an unfavourable environment for solar wind to produce significant amounts of water on the surface. The independent Indian work, which pertains to a different volcanic region altogether, too has led to the conclusion that water in the CBVC could have originated from episodic events of volcanic eruption and effusion of silicic magma. It thus has thus not only confirmed the presence of magmatic water but has also provided a quantitative estimate of it.
The presence of endogenous water/hydroxyl molecules was inferred from the distinct and prominent absorption lines in the 2800 nm wavelength region observed in spectra of the Compton-Berkovich Thorium Anomaly (CBTA) region of the complex. The CBTA region is an area of high concentration of radioactive thorium of about 5.3 microgram/gram while the surrounding areas contain only 0.06 microgram/gram of thorium. It has an area of 32 km x 18 km.
The work of Klima and others too had found an enhancement of concentration of elements such as Thorium in the central peak of Bullialdus. The two findings together suggest that all the endogenous hydrogen present at the time of formation of Moon did not boil off and remained trapped at the certain locations on the Moon associated with primary magmatic minerals such as thorium. The presence of such endogenous water could call for revision of models of Moon’s origin, points out Dr. Chauhan.
