SHAPE (Spectro-polarimetry of HAbitable Planet Earth) is an experimental payload onboard Chandrayaan-3 Mission for the study of spectro-polarimetric signatures of Earth in the near-infrared (NIR) wavelength range (1.0 – 1.7 μm). It is the only scientific payload on the Propulsion Module (PM) of the Chandrayaan-3 mission.

Figure 1: Chandrayaan-3/SHAPE observation of Earth from the lunar orbit (Jaiswal B et al, 2022)	Figure 2: Chandrayaan-3/SHAPE Flight Model

The main goal of this experiment is to characterise Earth's disc-integrated spectrum and polarisation signatures at various phase angles (Φ in Fig 1) from the vantage point of lunar orbit. This is to mimic the observation of a far-away exoplanet. The spectrum carries crucial information about the gases and surface features, whereas the polarisation is required to characterise the clouds. The key science questions which are aimed to be addressed with the proposed experiment are as follows:

• What could be the disc-integrated spectrum of an Earth-like exo-planet?
• What could be the disc-integrated 'polarisation' from an Earth-like exo-planet?
• How do these features change with exo-planet's rotation and revolution?

SHAPE (Flight Model shown in Figure 2) employs an Acousto-Optic Tunable Filter (AOTF) based dispersive element driven by a radio frequency (RF) source, and a pair of Indium Gallium Arsenide (InGaAs) detectors. The instrument has been conceptualized by the Space Astronomy Group (SAG) at U. R. Rao Satellite Centre (URSC), Bengaluru.