The Chandra's Surface Thermophysical Experiment (ChaSTE) is a scientific payload onboard the Vikram lander of India's Chandrayaan-3 mission, which successfully soft-landed near the lunar south pole on August 23, 2023. Developed by the Space Physics Laboratory (SPL) at the Vikram Sarabhai Space Centre (VSSC) in collaboration with the Physical Research Laboratory (PRL), Ahmedabad, ChaSTE is designed to study the thermal properties of the lunar surface and subsurface, a critical aspect for understanding the Moon's thermal behavior and planning future missions.

• Measure Temperature Profile: To record the vertical temperature gradient of the lunar regolith (topsoil) up to a depth of 100 mm.
• Assess Thermal Conductivity: To determine how heat is conducted through the lunar surface material, aiding in the creation of a thermal profile of the Moon.

• Thermal Probe: ChaSTE features a probe equipped with 10 Platinum Resistance Temperature Detectors (RTD Pt-1000 sensors) placed at varying depths along its length. The probe is inserted into the lunar regolith using a controlled penetration mechanism.
• Heater: A ribbon heater mounted near the probe's tip allows active experiments to measure thermal conductivity by heating the surrounding regolith and observing temperature responses.
• Material: The probe is made of a composite material (cyanate ester reinforced with glass fiber and cork) with low thermal conductivity (~0.16 W m^-1 K^-1) to minimize heat interference, while maintaining mechanical strength for penetration.

• First In-Situ Measurements: ChaSTE provided the first-ever in-situ temperature profile and thermal conductivity data from the Moon;s high-latitude south polar region (around 69.36°S, 32.34°E).
• Temperature Variations: During the lunar daytime (over ~150 hours), ChaSTE recorded temperatures at depths up to 100 mm. Surface temperatures reached as high as 70°C, significantly warmer than the expected 20–30°C, while at 80 mm depth, temperatures dropped to around -10°C, revealing a steep thermal gradient.
• Scientific Implications: These measurements help understand how solar heat interacts with the lunar surface, the depth of solar forcing, and the potential preservation of volatiles like water ice in shadowed regions.

Operational Details:

• Deployment: After the Vikram lander's landing, ChaSTE was deployed on August 24, 2023, using a Shape Memory Alloy actuator to release it from its stowed position. The probe was then driven 140 mm into the regolith in steps.
• Data Collection: Temperature data was collected continuously at 1-second intervals, providing a detailed thermal profile during its operational period of one lunar day (14 Earth days).

ChaSTE's data is groundbreaking because prior in-situ thermal studies (e.g., Apollo missions) were limited to equatorial regions. The south polar data enhances our understanding of the Moon's thermal environment, crucial for identifying subsurface locations with stable temperatures for future habitats or resource exploration. The unexpectedly high surface temperatures also challenge existing models and underscore the uniqueness of the polar region.