Chandrayaan-2: India’s orbiter validates earlier finding of water on the lunar surface

One of the significant findings of India’s Chandrayaan-1 mission was to detect the presence of water on the moon’s surface. A probe onboard India’s Chandrayaan-2 orbiter (second lunar mission) has not only validated the breakthrough made by its predecessor but also paved the way for future lunar exploration. 

According to ISRO scientists who were associated with both the Lunar projects, the data from Chandrayaan-2 would be used to build a lunar water map, which would further aid upcoming missions to the moon. 

The initial evidence for surface water came from the NASA-provided Moon Mineralogy Mapper (M3) experiment carried on the Chandrayaan-1 spacecraft. While this payload from NASA also detected evidence of water at the lunar poles, its finding was under question, owing to the limited wavelength that M3 (an imaging spectrometer) covered. The basic function of a Spectrometer is to take in light (reflected from a surface) and provide a graph of the output. However, in the case of the M3, its wavelength of 0.7 to 3 microns was not sufficient to ascertain and affirm the detection of water on the moon.

"With M3, we had reached the tip of the iceberg, but we needed double and triple confirmation. In a breakthrough for us, the data from the old M3 sensor and the new Chandrayaan 2 sensor matched. The orbiter of Chandrayaan-2 has a 5 micron (wider) spectrometer, hence it unambiguously confirms the findings of Chandrayaan-1, "Dr Mylswamy Annadurai, Former Director of ISRO’s UR Rao Satellite Center, told WION. 

He added that, with its nearly 7-year long mission life, the Chandrayaan 2 orbiter (in lunar orbit since Sept 2019) has the potential to create a moon terrain map that depicts the rocks, craters, ice deposits, water traces etc. Fondly known as India's ‘Moon Man ’, Dr Annadurai expressed hope that such a lunar map would help upcoming Indian lunar exploration missions and eventually the larger global scientific community. 

"The spectrometer on Chandrayaan-2 can detect the presence of water (H2O) molecules and also measure the
Oxygen-Hydrogen atoms are held together as Hydroxide (OH). In the new spectrometer images, the dips on the graph are visible, DR. A S Kiran Kumar, former Chairman of ISRO, told WION. 

According to him, the separation of wavelengths in the 3.1 and 3.2-micron regions helped distinguish between water and hydrogen. 

Water is detected as water molecules and hydroxides are found in minerals and hydrates. ISRO’s orbiter can map almost the entire moon (from its 100km altitude orbit) and more data can be collected from repeated observations, he adds. This offers good prospects for scientific analysis and studies, given that water (H2O) and hydroxide (OH) don’t exist in isolation on the lunar surface. Generally, water is found in the molecule form, whereas hydroxides are found as moisture in minerals and hydrates.

India’s second lunar mission, Chandrayaan-2 (launched in 2019), was only partially successful, as the lander ‘Vikram’ could not descend on the South Pole of the moon, as intended. Instead, the lander and the rover housed in it crashed landed, thus denying the opportunity to conduct a short-term, on-surface analysis. However, the orbiter, which circles the moon at an altitude of 100km and an approximate speed of 1km/s, continues to function and is expected to function for many more years. India’s first lunar probe, Chandrayaan-1, was launched in 2008 and it functioned for almost a year before communication was lost with the orbiter.