BENGALURU: A team of scientists from the Indian Space Research Organisation (ISRO) on May 18 shared a report of the findings of the ‘Hop’ experiment conducted by the Vikram Lander of Chandrayaan-3 and the Chandra’s Surface Thermophysical Experiment (ChaSTE) on the moon.
The researchers noted, “While we often call it lunar soil, the more apt term to be used is lunar regolith. The lunar regolith is actually shattered rock, tiny, jagged glass-like shards that are abrasive and cling to everything.”
They also pointed out that the complex structure of regolith has unique geo-technical and thermophysical properties. They said the top 2-6 cm regolith is found to be highly cohesive or sticky and hyper-porous, which can act as a thermal blanket.
This layer is crucial in the storage of water-ice molecules in the subsurface, and in selecting the sites for future scientific bases and habitat construction on the Moon.
The ISRO scientists said, “For an astronaut, this means the surface might feel like walking on dry flour, while just a few inches deeper. This is because, even at that small depth of a few centimetres, the bulk density changes from 750 to 1600 kg m⁻³.”
Understanding the thermal and physical properties of the moon’s regolith is important from both scientific and technological angles. They said the thermophysical characteristics of the regolith hold clues to some questions, like how the moon manages the solar heat input, or how much it absorbs and how much it radiates back to space.
The lander had conducted the Hop experiment on September 3, 2023, with a jump of around 50 cm, by utilising the residual propellant. In the ChaSTE, a sharp-tip, rod-shaped probe, with temperature sensors attached to its length and a heater at the tip, penetrated the moon’s regolith.
The hop manoeuvre allowed ChaSTE to analyse different locations and understand how the engine plume eroded the lunar surface. The list of critical finding included details pertaining to surface erosion and compaction, layered stratigraphy, geotechnical variability and twilight thermal profiles.
The teams noted details of the top 3cm of lunar loose dust, which was exposed when the lander’s engine was fired during the Hop experiment. The report stated: “Moon’s surface is not just one uniform pile of dust. By looking at the ‘hop’ site, the results suggested a distinct two-layer cake-like structure within the top few centimetres.”