Chandrayaan-1, India’s first mission to Moon, was launched with the prime objective of finding traces of water on the lunar surface besides mapping minerals and chemicals on the Moon. Towards this, a host of sophisticated instruments were included in Chandrayaan-1 spacecraft, like Moon Impact Probe (MIP) and Hyper-Spectral Imager (HySI) from ISRO as well as Moon Mineralogy Mapper (M3) and Miniature Synthetic Aperture Radar (Mini-SAR) through NASA to collect relevant data from the lunar surface. During the mission, excellent quality of data from all these instruments has been obtained. While M3 has covered nearly 97% of the lunar surface, some of the other instruments have covered more than 90%.
A path-breaking finding has evolved recently from the detailed analysis of the data obtained from M3, which has clearly indicated the presence of water molecules on the lunar surface extending from lunar poles to about 60 deg. Latitude. Hydroxyl, a molecule consisting of one oxygen atom and one hydrogen atom, was also found in the lunar soil. The confirmation of water molecules and hydroxyl molecule in the moon's polar regions raises new questions about its origin and its effect on the mineralogy of the moon.
M3 measures the intensity of reflected sunlight from the lunar surface at infrared wavelengths, splitting the spectral colours of the lunar surface into small enough bits revealing finer details of the lunar surface composition. This enabled identification of the presence of various minerals on the lunar surface that have characteristic spectral signature at specific wavelengths. Since reflection of sunlight occurs near the moon’s surface, such studies provide information on the mineral composition of the top crust of a few millimeters of the lunar surface. The Indian instrument HySI, that covers the wavelength region 0.4 to 0.9 micron, also provided additional data in this regard that helped in better understanding of moon’s mineral composition.
The findings from M3 onboard Chandrayaan-1 clearly shows a marked signature in the infrared region of 2.7 to 3.2 micron in the absorption spectrum, which provided a clear indication of the presence of hydroxyl and water molecules.
The scientific team, after detailed analysis, has come to the conclusion that there are traces of hydroxyl (OH) and water (H2O) molecules on the surface of the moon closer to the polar region. It is also concluded that they are in the form of a thin layer embedded in rocks and chemical compounds on the surface of the moon and the quantity is also extremely small of the order of about 700 ppm. These molecules could have come from the impact of comets or radiation from the sun. But most probable source could be low energy hydrogen carried by solar wind impacting on the minerals on lunar surface. This in turn forms OH or H2O molecules by deriving the oxygen from metal oxide.
Following these findings, the scientific team revisited the data from NASA’s Deep Impact Mission launched in 2005 which carried an instrument similar to M3. Deep Impact Probe observed the moon during the period June 2 and 9, 2009. This, along with some laboratory tests carried out from samples brought from Apollo missions, has confirmed that the signature is genuine and there is a thin layer of surface mineral which contains traces of hydroxyl and water molecules.
The M3 observations are further strengthened by results obtained from the analysis of archived data of lunar observation in 1999 by another NASA Mission, Cassini, on its way to Saturn. This data set also revealed clear signatures of both OH and H2O absorption features on the lunar surface.
The analysis of the huge volume of M3 data was carried out by a joint team of scientists from US and India. The lead role was taken up by Dr.Carle Pieters, Principal Investigator from Brown University, USA and Prof. J N Goswami, Principal Scientist, Chandrayaan-1 from Physical Research Laboratory of India`s Department of Space. The findings were published in Sciencexpress in its September 24, 2009 edition (Slides provided by ISRO to media ).
Analysis of data from other instruments on board Chandrayaan-1 is in progress.
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