Mapping Apollo 17's 73002 Sample
In a sealed tube for 50 years, a lunar core sample finally reveals its secrets through quantitative compositional mapping, rewriting the history of the Moon's landscape.
The Apollo 17 mission of 1972 marked the last time humans walked on the Moon. Astronauts Eugene Cernan and Harrison Schmitt did not just collect rocks; they carefully documented and preserved special samples for future generations. One of these was the 73002 double drive tube, a core sample collected from the base of the South Massif in the Taurus-Littrow Valley. Sealed under vacuum on the lunar surface, it remained unopened for nearly five decades until NASA's Apollo Next Generation Sample Analysis (ANGSA) program initiated its study as a bridge between the Apollo and Artemis generations 3 .
This article explores how scientists are using quantitative compositional mapping—a advanced technique that creates detailed, quantitative images of a sample's chemical makeup—to unravel the history locked within these precious lunar particles, revealing not just what the Moon is made of, but the dramatic processes that shaped its surface.
The 73002 core was collected from the base of the South Massif in the Taurus-Littrow Valley and was sealed under vacuum on the lunar surface to preserve its pristine condition.
The core was sealed on the lunar surface, preserving any volatile substances and its original structure, free from terrestrial contamination 3 .
The sample was collected from material believed to be a landslide deposit from the South Massif. Analyzing its composition could verify this origin and reveal the geological history of the massif itself .
The program involved a team of scientists, most of whom were not alive during the Apollo Program, facilitating a transfer of knowledge and setting the stage for future lunar exploration 3 .
"The ANGSA program was designed to function as a low-cost sample return mission, using pristine Apollo samples to test new technologies and methodologies for the upcoming Artemis program."
Quantitative compositional mapping goes far beyond taking a pretty picture. It involves sophisticated instruments that can measure the actual concentration of elements or minerals at every single point—or pixel—across a sample's surface.
Early "dot maps" from electron microprobes provided a qualitative glimpse of elemental distributions but lost all quantitative data and were poor at detecting low concentrations 2 . Modern quantitative mapping, however, involves recording full x-ray or mass spectrometry data at each point in a scan matrix. These intensity matrices are then converted into true concentration values using complex corrections and calibrations, resulting in an image where color directly corresponds to chemical composition 2 1 .
Primary Function: Automated mineral identification and mapping
Key Advantage: High-speed, large-area analysis revealing texture and mineral associations
This automated system uses an electron microscope to rapidly identify and map minerals across a sample based on their chemical composition and texture. It was the primary tool used to survey the entire core thin section .
Primary Function: Quantitative major and minor element analysis
Key Advantage: High accuracy for determining mineral chemistry; used for validation
This workhorse of geochemistry provides highly accurate quantitative measurements of major and minor element concentrations in minerals. It was used to verify the composition of interesting clasts found by QEMSCAN .
Primary Function: Trace element mapping and analysis
Key Advantage: Excellent detection limits for geologically critical trace elements
This technique uses a laser to vaporize tiny spots of a material and then analyzes the vaporized plasma with a mass spectrometer. It is exceptionally good for detecting trace elements that are geologically revealing but occur in very low abundances 1 .
Primary Function: Data reduction and image generation software
Key Advantage: Free, open-source platform for processing complex LA-ICP-MS data 1
This software tool is essential for processing the complex data generated by LA-ICP-MS and other mapping techniques, converting raw intensity data into meaningful chemical maps.
A crucial experiment in the analysis of the 73002 core was the automated mineralogy study performed using QEMSCAN, which aimed to systematically characterize the entire sample .
The upper portion of the 73002 core was carefully extruded and a series of continuous thin sections were prepared, capturing the entire length of the core for analysis.
The thin sections were loaded into the QEMSCAN instrument, which used a scanning electron microscope to analyze the sample point-by-point.
At each point, the system measured the elemental composition and compared it to a pre-defined spectral library to automatically identify the mineral present.
The software was programmed to highlight mineral groups associated with potential meteoritic origins, flagging them for further investigation.
Researchers extracted raw pixel data to analyze changes in mineralogy with depth and used processors to separate and group individual clasts based on their mineralogy.
The QEMSCAN analysis yielded several key findings that paint a vivid picture of the core's history.
The primary hunt was for non-lunar meteoritic fragments. The system identified 232 clasts of interest. However, follow-up analysis with the more precise electron microprobe confirmed that all 33 clasts analyzed were of lunar origin. This suggests any meteoritic component in this regolith is finely dispersed, not in the form of large, recognizable fragments .
In the process, scientists discovered a group of clasts with highly magnesian olivine (Fo92.2-96.5). This composition is considered primitive and likely originates from the Moon's lower crust or mantle, providing a tantalizing glimpse into the Moon's deep interior .
By tracking mineral abundance with depth, the team observed a decrease in glass and agglutinate (soil welded by impacts) clasts with depth. This is a key indicator of soil maturity—the longer the soil is exposed to space and micrometeorite bombardment, the more glass and agglutinates it contains. Thus, the upper part of the core has a higher maturity than the lower part .
The general lack of clear stratigraphy and the dominance of non-mare (non-plain) clasts throughout the core are consistent with the material being jumbled and transported in a landslide from the South Massif, confirming the geological context of the sampling site .
| Depth Zone | Glass & Agglutinate Abundance | Implied Soil Maturity |
|---|---|---|
| Upper Portion | Higher | More Mature |
| Lower Portion | Lower | Less Mature |
The quantitative mapping of the 73002 core does more than just describe one sample; it opens new doors for lunar science and future exploration.
The techniques refined through ANGSA, such as the sophisticated data reduction for LA-ICP-MS maps that allows for the quantification of inhomogeneous materials, are directly applicable to the samples that will be returned by the Artemis program 1 .
By confirming the landslide origin of the South Massif material, this research helps planetary scientists better understand slope processes and the structural evolution of the lunar surface.
"The analysis of the Apollo 17 core 73002 is a powerful testament to the foresight of the Apollo-era scientists who preserved these samples for the future."
Through the application of quantitative compositional mapping—transforming pixels into geochemical data—a new generation of scientists has unlocked a deeper narrative.
They have read the story of the landslide, measured the maturity of the soil, and caught a glimpse of the Moon's primitive interior, all while finding that the most expected clue, the meteorite fragment, was conspicuously absent. As we stand on the cusp of returning to the Moon, the lessons learned from this 50-year-old core ensure that the Artemis generation is better prepared than ever to uncover the Moon's enduring secrets.