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Findings from the Chandrayaan-3 Vikram lander's "hop" experiment, published in The Astrophysical Journal in April 2026, demonstrate significant heterogeneity in the Moon's surface composition at local scales — challenging previous assumptions about lunar soil uniformity and providing India's first in-situ geotechnical data from the lunar south polar region.

The Hop Experiment:

On 2 September 2023, engineers reignited Vikram's engines to perform a short vertical hop of approximately 50 centimetres using residual propellant. The manoeuvre was initially designed to validate re-ignition capabilities for future sample-return missions, but the engine exhaust inadvertently stripped away the top three centimetres of loose lunar dust, exposing denser material beneath — providing a unique opportunity to study subsurface regolith properties at the south pole for the first time.

The Chandra's Surface Thermophysical Experiment (ChaSTE) — equipped with temperature sensors and a heating probe that penetrated the regolith — was then redeployed at the new post-hop location, measuring thermal profiles during the twilight transition (16:25–17:30 lunar local time), a slow cooling period lasting hours due to the Moon's month-long day-night cycle.

Key Scientific Findings

Two-Layer "Cake-Like" Structure

The Moon's surface at the south pole exhibits a distinct, two-layer structure within the top few centimetres — not a uniform pile of dust as previously assumed.

Upper Layer (0–6 cm) — The "Fluffy Thermal Blanket": The top layer is hyper-porous and highly cohesive, behaving like loose flour near the surface. Bulk density increases dramatically from 750 kg/m³ at the surface to 1,600 kg/m³ at a depth of just 6.5 cm — where the material becomes significantly stiffer, behaving more like damp clay.

Thermal Behaviour:ChaSTE captured a sharp temperature drop after 17:00 lunar local time, as the absence of an atmosphere allows heat to radiate rapidly into space once the Sun's rays are blocked by local shadows — demonstrating how the hyper-porous top layer functions as a critical thermal insulator.

Supporting Evidence: 3D simulations using Chandrayaan-2's OHRC (Orbiter High Resolution Camera) high-resolution imagery confirmed the regolith's layered stratigraphy.

What is Lunar Regolith?

Scientists emphasise that the Moon's surface layer is more accurately termed "lunar regolith" rather than "lunar soil" — it consists of shattered rock fragments and jagged glass-like shards formed by billions of years of micrometeorite bombardment. Unlike terrestrial soil, it lacks organic material or water-formed minerals, and its jagged, angular particles create unusual mechanical properties — high cohesion yet extreme looseness at the surface.

Why It Matters: Five Implications

• Water-Ice Storage: The hyper-porous top layer is particularly significant for trapping water-ice molecules in the subsurface — critical for assessing the viability of in-situ resource utilisation (ISRU) at lunar south polar bases.
• Future Lunar Base Planning: The dramatic density gradient within just 6.5 cm means that drilling, foundation engineering, and habitat construction at the lunar south pole will require significantly different approaches than originally modelled — directly informing NASA's Artemis programme and ISRO's own lunar ambitions.
• Rocket Plume-Surface Interaction: Understanding how engine exhaust erodes the regolith is essential for safe landing zone design for future crewed and cargo missions — preventing landing struts from sinking into loose surface material.
• Sample Return Missions: The hop experiment validates critical engine re-ignition capabilities, setting a precedent for future sample-return missions.
• Chandrayaan-4 Design Inputs: India's upcoming Chandrayaan-4 mission — designed for lunar sample collection and return — will directly incorporate these findings in its lander design and landing site selection.