Imaging Infrared Spectrometer (IIRS) on-board Chandrayaan-2 is designed to measure the reflected sunlight and emitted part of Moon light from the lunar surface in narrow and contiguous spectral channels (bands) ranging from ~800 – 5000 nanometer (0.8-5.0 micrometer (µm)). It uses a grating to split and disperse the reflected sunlight (and emitted component) into different spectral bands. The major objective of IIRS is to understand the origin and evolution of the Moon in a geologic context by mapping the lunar surface mineral and volatile composition using signatures in the reflected solar spectrum.

The first illuminated image of the lunar surface was acquired by IIRS. The image covers part of the lunar farside in the northern hemisphere. Few prominent craters are seen in the image (Sommerfield, Stebbins and Kirkwood).

Preliminary analysis suggests that IIRS could successfully measure the variations in the reflected solar radiation that bounces off the lunar surface from different kinds of surface types, namely, crater central peaks (e.g., Stebbins), crater floors (e.g., Stebbins and Sommerfield), very fresh reworked ejecta associated with small craterlets within the crater floor of a large crater (e.g., Sommerfield) and also the sun-illuminated inner rims of craters (e.g., Kirkwood). The variations in the spectral radiance are primarily due to the mineralogical/compositional variations that exist in the lunar surface and also due to the effect of space weathering. More detailed analysis that follows, is expected to yield important results on the heterogeneity of lunar surface composition.

ISRO