What Happened
- A new study using data from Chandrayaan-3's Vikram lander hop experiment has revealed information about the near-surface layered structure ("surficial layers") of the lunar regolith near the south polar region.
- When Vikram fired its engines for the hop, the engine plume disturbed the top layer of lunar soil — the resulting seismic and surface data, captured by the onboard ILSA (Instrument for Lunar Seismic Activity) and ChaSTE (Chandra's Surface Thermophysical Experiment) instruments, allowed researchers to infer sub-surface stratigraphy.
- The findings add to a growing body of scientific output from Chandrayaan-3, which has already confirmed thermal gradients, mineral composition near the south pole, and the presence of multiple seismic signals including possible moonquakes.
- This study is significant because it demonstrates Vikram's hop — designed primarily as an engineering test for future sample-return and crewed missions — also yielded valuable scientific data about the lunar surface architecture near the pole.
Static Topic Bridges
Chandrayaan-3 Mission: Overview and Payloads
Chandrayaan-3 was India's third lunar mission and the first to achieve a soft landing on the Moon's south polar region. It was launched on July 14, 2023, aboard LVM3-M4 (GSLV Mk III) from SDSC SHAR (Sriharikota) and soft-landed on August 23, 2023 — a date now commemorated as National Space Day. The mission comprised a Propulsion Module, Vikram Lander, and Pragyan Rover. It made India the first country to land near the lunar south pole and the fourth nation to achieve a soft lunar landing.
- Launch vehicle: LVM3-M4 (GSLV Mk III); Launch site: SDSC SHAR, Sriharikota
- Landing date: August 23, 2023; Landing site named "Shiv Shakti Point"
- Mission life design: 1 lunar day (~14 Earth days); Pragyan rover traversed ~100 m
- Vikram payloads: RAMBHA-LP (plasma), ChaSTE (thermal), ILSA (seismic), LRA (laser retroreflector from NASA)
- Pragyan payloads: APXS (elemental analysis), LIBS (mineral composition)
- First detections: sulphur, aluminium, calcium, iron, chromium, titanium, manganese, oxygen near south pole (LIBS)
Connection to this news: The hop experiment used Vikram's propulsion system post-mission, generating controlled disturbance data that ILSA and ChaSTE recorded — turning a technology demonstration into a science experiment about surface layers.
Vikram Lander Hop Experiment
The hop experiment was performed on September 3–4, 2023, just before the end of the lunar day (lunar sunset). On command from ISRO, Vikram fired its engines, elevated to approximately 40 cm, moved laterally 30–40 cm, and soft-landed again. It was only the second time a spacecraft had performed a controlled hop on the Moon (after the Chinese Chang'e-5 lander's ascent stage). The fold-back-and-redeploy of ChaSTE and ILSA before and after the hop allowed these instruments to record pre- and post-disturbance data from the same site.
- Elevation during hop: ~40 cm; lateral displacement: 30–40 cm
- Purpose: validate re-ignition capability for future sample-return missions (collect-and-return architecture) and crewed landers
- All instruments redeployed successfully after the hop
- Engine plume interaction with regolith created a controlled disturbance — a natural seismic/thermal experiment
- Only the second lunar hop ever: first was Apollo 16's LM ascent stage, in a different context
Connection to this news: The engine plume from the hop disturbed the top soil layer in a known and controlled way, allowing scientists to use ILSA seismic readings and surface temperature data to back-calculate the mechanical and thermal properties of discrete subsurface layers — effectively a shallow seismic sounding experiment.
Lunar Regolith and South Pole Significance
Lunar regolith is the layer of loose, fragmented material (rock, dust, glassy particles from meteorite impacts) covering solid bedrock. Near the south pole, regolith properties differ significantly from equatorial regions due to lower temperatures, different solar illumination angles, and proximity to Permanently Shadowed Regions (PSRs) that may harbor water ice. The ChaSTE instrument had already shown a steep thermal gradient: surface peak temperature ~355 K (higher than expected due to local sunward slope), dropping to ~105 K just 10 cm below — a finding unprecedented for polar lunar latitudes.
- Lunar regolith depth varies from a few metres (highlands) to tens of metres depending on location and impact history
- South pole PSRs: temperatures as low as 40 K — among coldest natural environments in the solar system
- Water ice stability requires temperatures below ~110 K; sloped areas >14° near the south pole can maintain subsurface ice even outside PSRs (ChaSTE finding, March 2025)
- Chandrayaan-3 landing latitude: ~69.37°S — closest any spacecraft had landed to the lunar south pole at the time
- Surficial layers (~top 1–2 m) are critical for future lunar resource utilization (ISRU) — understanding their properties determines excavation difficulty, ice accessibility, and construction material availability
Connection to this news: Understanding the layered architecture of the regolith at this specific south polar location — what the hop study addresses — directly informs future lunar base site selection, ISRU planning, and human mission design.
ILSA: India's Lunar Seismometer
The Instrument for Lunar Seismic Activity (ILSA) on Vikram is the first seismometer deployed at the lunar polar region and the first since the Apollo missions (1969–1977) to record ground accelerations on the Moon. ILSA uses a MEMS (Micro-Electro-Mechanical Systems) accelerometer developed by CSIR-CEERI (Central Electronics Engineering Research Institute), Pilani, and measures ground vibration along vertical and two horizontal axes.
- Developed by: ISRO Space Applications Centre (SAC), Ahmedabad; MEMS sensor by CSIR-CEERI, Pilani
- First-ever seismic instrument at the lunar south polar region
- Recorded 250+ signals during the mission; ~50 unattributed to rover/instrument activity (potential moonquakes)
- Published findings in Planetary and Space Science (2024) and Earth and Space Science (Wiley, 2025)
- The hop experiment created a known, controlled seismic event — a valuable calibration and sounding reference
Connection to this news: ILSA's recordings during and after the hop provide the raw data used to infer the mechanical layering of the near-surface regolith — the seismic wave propagation through different density layers is the physical mechanism behind the surficial layer findings.
Key Facts & Data
- Chandrayaan-3 launch: July 14, 2023 (LVM3-M4); soft landing: August 23, 2023 (Shiv Shakti Point, ~69.37°S)
- India is the 4th country to achieve a lunar soft landing; 1st to land near the south pole
- August 23 declared National Space Day by PM Modi
- Vikram hop: ~40 cm elevation, 30–40 cm lateral displacement; performed September 3–4, 2023
- ChaSTE thermal finding: surface ~355 K; just 10 cm depth ~105 K (steep polar thermal gradient)
- ILSA recorded 250+ seismic signals; ~50 are candidate natural moonquakes — first polar moonquake data
- Water ice stability threshold: <110 K; south polar slopes >14° can maintain subsurface ice (March 2025 study)
- Pragyan LIBS detected sulphur, aluminium, calcium, iron, titanium, oxygen at landing site — first in-situ elemental confirmation near lunar south pole
- LVM3 (GSLV Mk III): India's heaviest launch vehicle; payload to GTO: ~4 tonnes; to LEO: ~8 tonnes