An Open Database of Lunar Regolith and Simulants Properties

This paper presents an open-access database and user interface that centralizes fragmented historical and contemporary data on lunar regolith physical and geotechnical properties, as well as simulants, to enhance their accessibility and usability for scientific and engineering research.

The Gist

Imagine the Moon's surface isn't a solid rock, but a giant, ancient beach made of dust, broken glass, and sharp rocks. Scientists call this "lunar regolith." If we want to send rovers, build bases, or land safely there, we need to know exactly how this "sand" behaves. Does it hold weight? Is it sticky? Does it slide easily?

For decades, the answers to these questions were scattered like puzzle pieces across thousands of old, dusty reports from the Apollo missions (1960s-70s), Soviet Luna missions, and newer Chinese and Indian probes. Some were in hard-to-read formats, some were in different languages, and some were just buried in PDFs that were hard to search.

The Solution: A "Library of Moon Dust"
The authors of this paper have built a new, free, online database that acts like a central library for all this information. They didn't just dump the data in; they organized it, cleaned it up, and built a user-friendly website where anyone can search, filter, and visualize the data.

Think of it as a "Google Maps for Moon Soil." Just as you can zoom in on a city map to see traffic or terrain, this tool lets scientists zoom in on specific Moon landing sites to see exactly how the soil behaved there.

How They Built It

The team acted like digital archaeologists. They dug through:

• Old Mission Reports: From the first soft landings in the 1960s to the latest robotic missions in 2025.
• Different Ways of Testing:
  • In-Situ (On the Moon): Looking at footprints, rover tracks, or how lander legs sank into the ground.
  • On Earth: Analyzing the actual rocks and dirt brought back by astronauts.
  • Remote Sensing: Using satellite photos to see how boulders rolled down hills.
• Simulants: They also included data on "fake moon dust" (simulants) made in labs on Earth. These are crucial because engineers need to test their equipment on Earth before sending it to the Moon.

What They Found (The "Aha!" Moments)

The paper uses this database to answer three big questions, using simple comparisons:

1. Is Moon Dust the same everywhere?
Scientists used to think the "Highlands" (the bright, mountainous parts of the Moon) had very different soil than the "Maria" (the dark, flat plains).

• The Analogy: Imagine thinking all sand on a beach is the same, but then realizing the sand near the dunes is different from the sand near the water.
• The Finding: The database shows that the soil properties are actually more similar than we thought. While there are some differences, the soil in the mountains isn't radically different from the soil in the valleys. The biggest factor isn't where you are, but how deep you dig. The soil gets denser and stronger the deeper you go, just like packing down snow.

2. Does the Moon feel different than Earth?
When we test soil on Earth, we have 100% gravity. On the Moon, gravity is only 1/6th as strong.

• The Analogy: Imagine trying to walk in a heavy winter coat on Earth versus walking in that same coat while floating in a swimming pool. The way you move and how the fabric behaves changes completely.
• The Finding: The database reveals a clear split. Soil tested on the Moon (in low gravity) behaves differently than soil tested on Earth (in high gravity), even if it's the same dirt. The Moon soil seems to have less "stickiness" (cohesion) but holds its shape better in some ways. This means you can't just take Earth soil rules and apply them to the Moon; the environment changes the rules of the game.

3. Are our "Fake Moon Dusts" good enough?
Engineers make "simulants" (fake moon dust) to test drills and rovers on Earth.

• The Analogy: It's like trying to practice skiing on a dry, sandy hill before going to a real snowy mountain. If the sand is too sticky or too loose, your practice won't help you.
• The Finding: The database shows that most fake moon dust is too sticky compared to the real thing. Real moon dust is sharp and angular, like broken glass, which makes it slide differently than the rounder particles in our fake dust. This explains why, during the Apollo 15 mission, astronauts struggled to drill deep holes—their Earth-based tests didn't predict how hard the real Moon soil would be.

Why This Matters

This paper isn't just a list of numbers; it's a toolkit for the future.

• For Engineers: It helps them design rovers that won't get stuck and drills that won't break.
• For Scientists: It lets them compare old data with new data instantly to spot trends.
• For Everyone: It's an "Open Science" project, meaning anyone can use it, and the authors invite the community to add new data as we learn more from future missions.

In short, the authors have taken a messy, scattered history of Moon exploration and turned it into a clear, interactive map that helps us understand the ground we'll be walking on next time we visit the Moon.

Technical Summary

Technical Summary: An Open Database of Lunar Regolith and Simulants Properties

Problem Statement
Lunar regolith properties are fundamental to the design of surface infrastructure, mobility systems, and in-situ resource utilization (ISRU) for lunar exploration. However, critical data regarding these physical and geotechnical properties remain fragmented across decades of mission reports (ranging from the 1960s to contemporary missions). This data is often dispersed across incompatible formats, archived in scanned documents, or locked in original languages, making integration, comparison, and re-analysis difficult. Consequently, the scientific community lacks a centralized, accessible, and standardized repository to support the new generation of lunar missions driven by programs like NASA's Artemis and emerging commercial and international efforts.

Methodology
The authors developed a comprehensive, open-access database and a corresponding web-based user interface to centralize lunar regolith data.

• Data Curation: The team systematically reviewed technical documents from NASA Surveyor, Apollo, Soviet Luna, and recent missions (Chang'E, Chandrayaan), as well as reinterpretation papers. Data extraction was performed manually to ensure accuracy given the unstructured nature of historical sources.
• Data Scope: The database aggregates data from three primary sources:
  1. Direct in-situ measurements from crewed and robotic missions.
  2. Estimates inferred from surface interactions (e.g., rover tracks, footprints, lander padprints).
  3. Laboratory analyses of returned samples conducted on Earth.
  4. Data on lunar regolith simulants used for terrestrial testing.
• Parameters: The database records key geotechnical parameters, including the angle of internal friction, cohesion (Mohr-Coulomb model), bulk density, static bearing capacity, porosity, and grain density. It also captures metadata such as testing methods (e.g., penetrometer, trench, direct shear), geographic coordinates, test location (in-situ, on Earth, or remote), and environmental context (e.g., local gravity).
• Architecture: The system is built on Python using the Streamlit framework. It stores data in CSV format and offers a web application for interactive filtering, visualization, and export. The architecture includes separate datasets for true regolith, simulants, combined data, and general bulk interpretations, alongside mission-specific detail pages.

Key Contributions

1. Centralized Repository: The paper presents the first unified database linking historical mission data (1966–2025) with modern interpretations and simulants data, covering over 200 entries.
2. Open-Science Interface: A user-friendly web application allows researchers to filter data by mission, terrain type (mare vs. highland), testing method, and parameter range. It enables the generation of customized plots for comparative analysis without requiring programming skills.
3. Standardization of Testing Methods: The authors classify diverse testing methodologies (e.g., spacecraft touchdown analysis, penetrometers, core tube extraction, boulder track analysis) to facilitate the comparison of heterogeneous data sources.
4. Simulant Integration: The database explicitly links simulants to their target lunar regolith properties, providing a "Moon-truth" reference for evaluating the fidelity of terrestrial test materials.

Results and Use-Cases
The paper demonstrates the database's utility through three specific use-cases:

• Terrain Comparison: Analysis of in-situ data across mare and highland terrains reveals that while some differences exist (e.g., bulk density), the geomechanical properties (internal friction angle, cohesion) are more variable within terrain types than between them. This suggests that local geological history and impact processes may be more significant than broad terrain classification.
• In-Situ vs. Earth-Based Measurements: A comparison of in-situ lunar data with Earth-based tests on returned samples shows systematic differences. In-situ measurements generally exhibit higher internal friction angles and lower cohesion. The authors note that environmental factors, particularly reduced gravity, significantly influence granular behavior, meaning material properties are often a characterization of the material within its specific environment rather than an intrinsic constant.
• Simulant Selection: The database highlights discrepancies between true lunar regolith and simulants. While simulants often match the internal friction angle, they frequently exhibit higher cohesion than true in-situ regolith. This is attributed to particle morphology differences (angularity and void space), underscoring the risk of using inappropriate simulants for mission planning, as evidenced by historical drilling difficulties during Apollo 15.

Significance
The paper positions the database as a critical tool for bridging the gap between historical mission data and contemporary engineering needs. By making fragmented data accessible and comparable, the resource supports:

• Scientific Research: Enabling the reinterpretation of past results with modern analytical tools and facilitating studies on the influence of reduced gravity on granular materials.
• Engineering Design: Providing essential data for rover mobility analysis, lander design, excavation strategies, and ISRU system planning.
• Community Growth: Established as an open-science framework, the database is designed to evolve through community contributions, ensuring it remains a living resource for future lunar exploration programs (e.g., Artemis, Chang'E 6–7).

The authors emphasize that while the database improves data accessibility, it does not eliminate the inherent uncertainties of historical measurements. Future work aims to incorporate uncertainty quantification, expand to chemical composition data, and integrate with planetary GIS platforms.