Chandrayaan-3 "Hop" Experiment Reveals Hidden Lunar Secrets: Scientists Uncover Regolith Heterogeneity at Moon’s South Pole
Home /Chandrayaan-3 "Hop" Experiment Reveals Hidden Lunar Secrets: Scientists Uncover Regolith Heterogeneity at Moon’s South Pole

May 18, 2026

The Vikram lander of Chandrayaan-3 soft-landed on Moon’s surface on August 23, 2023. After having conducted experiments on the lunar surface, near-surface plasma, as well as ground vibrations for a period of around 10 Earth-days, on September 02, 2023, the Chandrayaan-3 Vikram lander reignited its engines to perform a "hop" (~50 cm)by utilising the residual propellant.This 'hop' proved a critical skill for future missions that will bring lunar samples back to Earth.To be scientifically accurate, it is note worthy that while we often call it 'lunar soil', the more apt term is the ‘lunar regolith’. The lunar regolith is actually 'shattered rock'- tiny, jagged glass - like shards that are incredibly abrasive and cling to everything like static electricity. Understanding the thermal and physical (together referred to as ‘thermophysical’) properties of lunar regolith is important from both the scientific and technological perspectives. The ‘thermophysical characteristics’ of the regolith hold the clues to the question, how Moon manages the solar heat input; how much does it absorb, and how much is radiated back to space?

This is exactly what Chandra’s Surface Thermophysical Experiment (ChaSTE) did on the Moon. ChaSTE was a sharp-tip, rod-shaped probe, with temperature sensors mounted along its length, and a heater mounted at its tip, onboard the Vikramlander to penetrate the lunar regolith. Thehop maneuverof Vikram lander allowed the ChaSTE toanalyze a different location, observing how the engine plume eroded the lunar surface. This also helped acquiring measurements during the lunar twilight period (a person on the Moon would feel it is approximately 4:25 - 5:30 PM, seeing the relative position of the Sun with respect to the horizon; it is called the ‘local time’). It is to be noted that a single day-night cycle on Moon lasts nearly a month on the Earth. This means 'twilight' on Earth is not a few-minutes-long sunset that we are habituated to see on Earth; it is, rather, a slow transition that lasts for hours, offering scientists an opportunity to watch the ground cool down in slow motion.This opportunity enabled Physical Research Laboratory (PRL) scientists to derive the thermophysical, geotechnical characteristics and unique thermal response of the upper layer of the lunar regolith, at the high-latitude highland, where the Chandrayaan-3 landed.

The measurements by ChaSTE, particularly its penetration force and temperature profiles,indicated that the re-ignition of the lander engines resulted in erosion of the upper few centimetres of the regolith layer. This disruption led to the removal of the topmost “fluff” layer; a change that was directly captured in ChaSTE measurements, which was otherwise not observable.

Furthermore, the 3-D model simulations (software simulation to mimic the physical phenomena)supporting ChaSTE measurements using Chandrayaan-2’s OHRC high-resolution data, highlighted the complex structure of regolith with unique geo-technical and thermophysical properties. The top 2 to 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 base and habitat construction on the Moon

Figure 1(a) Temperatures measurements from ChaSTE within the top 6.5 cm of the regolith at the Post-hop location, during 16:20 – 17:17 hours Local Time. While ChaSTE observations at different depths are plotted as solid circles, solid lines represent the interpolated values to cover data gap.

Figure 1(a) Temperatures measurements from ChaSTE within the top 6.5 cm of the regolith at the Post-hop location, during 16:20 - 17:17 hours Local Time. While ChaSTE observations at different depths are plotted as solid circles, solid lines represent the interpolated values to cover data gap. ChaSTE observations have maximum uncertainty of ±0.5K. Variation of Sun elevation angle (Blue Stars) at the post-hop location is also shown for correlation.1(b) Blown-up image of temperature variation during cool-down phase. Magnitude reversal in temperatures at depths of 3mm and 13 mm respectively indicate the probability of a higher conducting layer at the top.

Figure 2 Schematic of ChaSTE insertion in the lunar surface

Figure 2 Schematic of ChaSTE insertion in the lunar surface

To summarise, the critical findings regarding the lunar regolith (soil) are:

  1. Surface Erosion and Compaction:When the lander’s engines fired for the 'hop,' the exhaust acted similar to a blower, stripping away the top 3 cm of the loose dust. This exposed the older, more tightly packed lunar material underneath.
  2. Layered Stratigraphy:The analyses revealed that the 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 centimeters. These layers show how the lunar surface has been hammered and crushed by micrometeorite bombardments since the solidification of the lunar crust.
  3. Geotechnical Variability:The soil becomes surprisingly grippy (highly cohesive) just a few centimeters down. At the surface, the dust is light, but at a depth of only 6.5 cm, it becomes twice as dense and five times more cohesive (changes from 300 Pa to 1600 Pa). For an astronaut, this means the surface might feel like walking on dry flour, while just a few inches deeper, it behaves more like damp, stiff clay. This is because, even at that small depth of a few centimeters, the bulk density changes from 750 to 1600 kg m⁻³.
  4. Twilight Thermal Profiles:ChaSTE captured a unique "twilight transition" dataset, showing a sharp temperature drop after 17:00 hours local time on Moon. At twilight, the shadows are long, and fast-moving. Due to the absence of air, the illuminated and shadowed regions display a stark temperature difference. The moment when the Sun’s rays stop hitting a specific spot (thus causing a shadow), the heat energy is radiated away into the vacuum of space almost instantly.

These findings provide more insight for surface operations in the lunar southern polar region. Understanding the local-scale heterogeneity (high diversity in surface characteristics within a short distance) is essential for future lunar exploration plans, especially for constructing scientific bases on the Moon. This study marks the first of such class of unique measurements.

Reference:
“In Situ Temperatures, Regolith Properties, and Evidence of Erosion at Chandrayaan-3 Post-hop Location from ChaSTE Twilight Observations”, K. Durga Prasad et al. 2026 ApJ 1001 135, DOI 10.3847/1538-4357/ae5228