BENGALURU: A payload aboard India’s Chandrayaan-2 orbiter, which is orbiting the Moon since August 2019, has for the first time mapped the abundance of sodium on the Moon. This finding improves upon the already known data based on successive laboratory investigations of returned samples of Apollo, Luna and Chang’e missions, besides from India’s own first lunar mission Chandrayaan-1’s X-ray Fluorescence Spectrometer (C1XS) which detected sodium from its characteristic line in X-rays that opened up the possibility of mapping sodium on the Moon.
Although these data widened the range of sodium composition on the Moon, the fundamental conclusions had persisted till now. In a recent work published in The Astrophysical Journal Letters, Chandrayaan-2 mapped the abundance of sodium on the Moon for the very first time using the Chandrayaan-2 Large Area Soft X-ray Spectrometer (CLASS) on board the orbiter. Built at the UR Rao Satellite Centre of the Indian Space Research Organisation (ISRO) in Bengaluru, CLASS provides clean signatures of the sodium line thanks to its high sensitivity and performance.
The new findings from India’s second unmanned lunar mission, Chandrayaan-2, provide an avenue to study surface-exosphere interaction on the Moon, which would aid the development of similar models for Mercury and other airless bodies in our Solar System and beyond. The study found that a part of the signal could be arising from a thin veneer of sodium atoms weakly bound to the lunar grains.
Since 1988, ground telescopes have taken images of this faint sodium glow around the Moon, which is just the colour of light emitted by a sodium vapour lamp. What has been elusive so far is the source of these atoms on the Moon’s surface.
According to ISRO, the radiance that fills the vast expanse of the night sky is the reflection of sunlight from the Moon’s surface, a major part of which is from the bright lunar highlands. The rock and soil samples that the Apollo 11 astronauts brought back to Earth showed that the regions on the lunar surface, which are remnants of the ancient lunar crust, are mainly composed of silicate minerals, including sodium.