More to come

THE discovery of water on the moons surface by the Moon Mineralogy Mapper (M3), a scientific instrument of NASA on board Chandrayaan-1, is the first of the findings by the instrument and we expect more to come, M. Annadurai, Project Director, Chandrayaan-1, said.

He pointed out that the mass spectrometer named ChACE (Chandras Altitudinal Composition Explorer), a payload on the MIP of Chandrayaan-1, had detected water vapour in the moons thin atmosphere. The MIP was built by the ISRO and was made to crash on the moons surface on November 14, 2008.

Annadurai said finding water on the moon was one of the several objectives of the Chandrayaan-1 mission and it had been achieved. The mission was technically 100 per cent successful, he asserted. Voluminous data had been received from all the 11 instruments that were flown on the spacecraft and they were being studied, he said.

He took the stand that the water on the lunar surface was being generated on the moon itself. The discovery, he said, had belied theories that the water on the top surface of the moon could have come from outside sources, that is, other planetary bodies. He made these observations in an interaction with students of the South Indian Educational Society (SIES) College in Mumbai on September 26.

Another theory is that comets and meteors that crashed on the moon over millions of years ago could have brought the water. Annadurai argued that the Chandrayaan-1 mission had altered that thinking.

The new theory is that the water molecules were not from an outside source but were being generated then and there [on the moon itself]. This is being analysed now. He revealed that the water molecules were found in the sunlit region of the moon. The earlier thinking was that water ice could exist only in the permanently shadowed regions of the moon. We are analysing this phenomenon also, he told the students.

An ISRO press release on September 24 said Chandrayaan-1 was launched with the prime objective of finding traces of water on the moon besides mapping its chemicals and minerals.

Towards this, several sophisticated instruments were included in the spacecraft. They included M3 and Mini-Synthetic Aperture Radar (Mini-SAR), both of NASA, and the MIP and the Hyperspectral Imager (HySI) of the ISRO to collect relevant data from the lunar surface. During the mission, data of excellent quality were obtained from all these instruments.

While M3 covered nearly 97 per cent of the lunar surface, some of the other instruments covered more than 90 per cent.

The press release described as path-breaking the finding from the data obtained from M3 that clearly indicated the presence of water molecules on the lunar surface, extending from the lunar poles to about 60o latitude.

It added: 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 molecules in the moons polar regions raises new questions about its [the moons] origin and its effect on the mineralogy of the moon.

Chandrayaan-1s scientific team, after a detailed analysis, had concluded that there were traces of hydroxyl (HO) and water (H2O) molecules on the surface of the moon closer to the polar region, the press release said. The team also concluded that they were in the form of a thin layer embedded in rocks and chemical compounds on the surface of the moon and the quantity was extremely small, of the order of about 700 parts per million.

[T]he most probable source [of water molecules] could be low-energy hydrogen carried by solar winds impacting on the minerals on the lunar surface. This, in turn, forms OH or H2O molecules by deriving oxygen from metal oxide, it added.

The analysis of the huge volume of M3 data was done by a joint team of scientists from the United States and India. The lead role was taken by Dr Carle Pieters, Principal Investigator from Brown University, U.S., and Dr J.N. Goswami, Principal Scientist, Chandrayaan-1 mission, and Director, Physical Research Laboratory, Ahmedabad.

ISRO Chairman G. Madhavan Nair told a press conference in Bangalore on September 25 that Chandrayaan-1 had detected water on the moon as early as June 2009. The mass spectrometer on board the MIP picked up clear signatures of water during its descent towards the moon, he said. This finding was later confirmed by the discovery of the M3, Madhavan Nair said.

Informed ISRO officials said there were possibilities that Mini-SAR, one of the scientific instruments on Chandrayaan-1, might have found water ice in the permanently shadowed polar regions of the moon.

Mini-SAR was developed jointly by the Applied Physics Laboratory of Johns Hopkins University and the Naval Air Warfare Centre, both in the U.S., and it came through NASA.

T.S. Subramanian