Kamal Ghorui
BENGALURU: When Vikram, India’s Moon lander, briefly lifted off and settled back down on the Moon in 2023, it marked a small but telling moment in the Chandrayaan-3 mission. Now, that short “hop”, which lasted around 3 minutes, is helping scientists piece together what lies just beneath the lunar surface, with very fine measurements.The manoeuvre, carried out towards the end of the mission, shifted the lander by about half a metre, giving researchers a rare chance to study a nearby patch of untouched ground and compare it with the original landing spot.Once the lander settled, a temperature probe called ChaSTE (Chandra’s Surface Thermophysical Experiment), a key instrument on the lander, was pushed into the soil again. This time, only five of its ten sensors managed to penetrate the ground, as the new spot sat on a slightly steeper slope within a small crater. Even so, it recorded how heat moved through the ground during the brief window before sunset — roughly one lunar hour of observations, with some gaps due to mission constraints.The findings come from a study led by K Durga Prasad at the Physical Research Laboratory (PRL), published in The Astrophysical Journal.The results show that the Moon’s surface is not uniform. Instead, it is made up of layers that behave differently. The top few centimetres form a layer that conducts heat more easily, while the material below is less conductive. This layered structure changes how the surface heats up during the day and cools down as night approaches.The hop itself also altered the ground. When Vikram fired its engines, the force appeared to have blown away around 3 cm of the uppermost soil, exposing denser material underneath. In effect, the lander unintentionally “dug” into the surface without using a drill. Intriguingly, this kind of localised disturbance over just half a metre was unexpected — the soil’s properties are typically uniform across such short distances.This revealed another key feature. The soil becomes more compact with depth. Near the surface, it is loose and porous, but within just a few centimetres, it becomes denser and more tightly packed. Such variations can affect how stable the ground is for landers and rovers. These measurements also differ notably from what Apollo and Surveyor missions found at equatorial sites decades ago, suggesting the polar region has its own distinct character.The probe also tracked temperature changes during twilight. As sunlight faded, the ground cooled steadily before temperatures dropped sharply. The upper layer reacted faster than the lower layers, again pointing to differences in structure.These findings matter beyond this single experiment. The Chandrayaan-3 landing site lies in the Moon’s southern polar region, an area of interest because it may contain frozen water. Understanding how heat moves through the soil can help scientists estimate where such ice might survive and remain stable.The study also shows how sensitive the lunar surface is. Even a brief engine firing changed the top layer enough to expose what lay beneath. Future missions, especially those aiming to collect samples or build infrastructure, will need to take such effects into account.In the end, a hop lasting around three minutes has offered a clearer picture of the Moon’s surface, showing that even small movements can yield valuable scientific clues.
