Back to the Future:
Linking Apollo and Artemis Generations of Lunar Explorers with Special Samples from the Moon
Over a period of only 41 months from July 16, 1969, to December 19, 1972, six human missions landed on the Moon as part of the Apollo program. During this very short period, human activity and capability expanded for each mission on the lunar surface. For example, during Apollo 11 astronauts carried out one extravehicular activity (EVA) that lasted approximately 2.5 hours during which they traveled approximately 165 meters (540 feet) away from the Lunar Module (a total distance traveled of 610 meters, or 2000 feet). A short 40 months later, Apollo 17 astronauts carried out three EVAs that lasted approximately 22 hours during which they traveled 10 kilometers (6 miles) away from the Lunar Module (for a total of more than 35 kilometers, or 22 miles). Enabled by the evolving surface capabilities, the sampling of the lunar surface dramatically evolved in capacity and complexity. Twenty-one and a half kilograms (47.5 pounds) of samples were collected during the Apollo 11 mission, whereas Apollo 17 collected 111 kilograms (244 pounds) of samples. In total the Apollo program returned 381 kilograms (840 pounds) of samples from the Moon’s surface. The Apollo samples were collected in different manners and stored in several types of innovative containers. The sophistication of lunar sampling continued to evolve during the program. Following Apollo 17, humans have never again returned to the lunar surface.
The Apollo legacy continued over the last 50 years with the samples that were returned. The analyses of these samples provided fundamental insights into the origin and history of the Earth-Moon system and how planets and even solar systems work. The samples have provided ground truth for every post-Apollo mission to the Moon for the interpretation of remotely sensed data. After 50 years of analyses and study, our sophistication for handling and examining samples has greatly increased. Some samples that were collected and preserved in special containers or represented unique lunar environments remain unexamined by standard or advanced analytical approaches. The Apollo Next Generation Sample Analysis (ANGSA) initiative was designed to examine a subset of these special samples. The ANGSA consortium consists of nine original teams funded by NASA plus international partners (e.g., the European Space Agency, or ESA). The initiative was purposely designed to function as a new sample return mission with processing, preliminary examination, and analyses utilizing new and improved technologies and recent mission observations. The ANGSA initiative links the first generation of lunar explorers who participated in the Apollo program with future explorers of the Moon during the Artemis program (Fig. 1).
Apollo Program Special Samples
With great foresight, Apollo mission planners and sample scientists devised sample collection, containment, and preservation approaches that more rigorously attempted to capture delicate and potentially transitory characteristics of lunar samples that were disturbed or lost during standard sample collection, curation, and handling. Very early on in the Apollo program there was an overarching philosophy of preserving samples for future generations. This philosophy has continued for the last 50 years.
The teams involved in the ANGSA initiative are examining three distinct types of special samples: (1) Apollo 17 (A-17) double drive tube, consisting of an unopened vacuum-sealed core sample (73001; Core Sample Vacuum Container, or CSVC) and its unsealed but unstudied companion core (73002); (2) drill core and shadowed samples that were placed in cold storage approximately one month after their return in the early 1970s; and (3) Apollo 15 Special Environmental Sample Container (SESC) samples opened in an organically clean helium cabinet and continuously stored in helium.
In many cases, the purpose of samples placed in sealed containers was to protect characteristics that could be modified by interactions with spacecraft cabin conditions, Earth’s environment, or agitation of regolith samples. A total of nine containers of lunar samples were sealed on the lunar surface and transported to Earth during the Apollo program. The Gas Sample Containers (GSC), SESC, and CSVC have knife-edge-indium seals (Fig. 2). Current unopened samples include two CSVCs (69001 and 73001) and an SESC (15014). For the CSVC used during the Apollo 16 and 17 missions, aluminum drive tube cores were sealed with Teflon caps and immediately placed in the CSVC on the lunar surface. Upon return to the Lunar Receiving Laboratory each CSVC was placed in an additional vacuum container. The vacuum containers were placed in Teflon bags and stored in the Lunar Laboratory Pristine Sample Vault. These three unopened samples combined contain 1.7 kilograms (3.7 pounds) of unstudied and possibly pristine lunar material. This exceeds the mass returned by all the robotic Soviet Luna missions and projected returned masses for many proposed NASA lunar robotic missions (e.g., MoonRise, Isochron). As such, each unopened sample should be treated as an individual lunar mission with science goals appropriate for the lunar environment they represent.
Sampling a Lunar Landslide with a Double Drive Core
The A-17 double drive tube samples 73001 and 73002 are targets for the ANGSA initiative. The double drive tube core penetrated a lunar landslide deposit in the Taurus-Littrow Valley. The light mantle landslide deposit is derived from the South Massif of the Taurus-Littrow Valley and extends onto the valley floor (Fig. 3). The deposit appears to represent multiple landslide events. One of the Apollo program science goals for this double drive tube was to sample potential gases derived from the Lee-Lincoln scarp and trapped within the overlying landslide deposit. The double drive tube was collected adjacent to Lara Crater at Station 3 during the second Apollo 17 EVA. Astronauts Eugene Cernan and Harrison Schmitt collected surface samples and collected the core by hammering the aluminum double drive tube into the deposit (Fig. 4). The total double drive tube core length was approximately 71 centimeters (28 inches) long with 73001 representing the deeper part of the core. At the time it was collected, the temperature at the bottom of the core was estimated to have been approximately 250°K with very limited temperature fluctuations. Sample 73001 was placed in a CSVC on the lunar surface and its upper companion core resided unexamined (until November 2019) in a sealed aluminum double drive tube.
In addition to these sealed samples, the ANGSA initiative will examine Apollo samples that were handled and curated using non-standard approaches (e.g., frozen, helium processing). Upon return, several A-17 sample splits for deep drill core 70001–70006, permanently shadowed soils (72320, 76240), soil (70180), and vesicular high-titanium basalt (71036) were permanently frozen at 253°K. Samples from an Apollo 15 SESC (15012/13) were removed from the SESC and processed in an organic clean space under helium atmosphere rather than nitrogen at the University of California Berkeley. They have been continuously stored in helium at the Johnson Space Center (JSC).
ANGSA Science and Engineering Goals
The ANGSA initiative has numerous investigations being pursued using the samples in the A-17 Station 3 double drive tube, frozen samples, and helium stored samples. Together, these samples leverage the uniqueness of sample containment (e.g., CSVC, SESC), geological setting (e.g., landslide, permanently shadowed areas), and curation processing (e.g., frozen for over 47 years, organic clean lab, helium curation). The following summarizes examples of ANGSA science and engineering goals.
Exploring volatile reservoirs and volatile cycles on the Moon
Over the last decade numerous studies and missions have pointed to a lunar volatile cycle with three principal components: primordial (interior) volatiles, surficial-formed volatiles (space-surface interactions), and polar (sequestered) volatiles. These reservoirs and their in situ resource utilization potential are important for the future human exploration of the Moon and beyond (e.g., Mars) within the aspirations of the Artemis program. Exploring the Moon and commercializing cis-lunar space by “living off of the land” versus bringing all consumable necessities from Earth has two dramatically different human exploration architectures, and therefore an understanding of the lunar volatile cycle has science, exploration, and commercial importance.
Lunar regolith contains evidence for these various volatile reservoirs, their origins, and their interactions. The CSVC may better preserve weakly-bound volatiles and volatile coatings on mineral surfaces as well as limited contamination of lunar hydrogen species, xenon, lead isotopes, and organic compounds. The results of this integrated study of volatiles in lunar regolith and lithic clasts will shed light on (1) the concentration, distribution, and behavior of volatiles in the lunar regolith; (2) the role of volatiles in lunar processes; (3) whether volatiles from the lunar interior are released from fault systems; (4) the interactions among lunar volatile reservoirs; (5) the potential existence of pre-mare degassing events; (6) the noble and other gas composition of the solar wind as recorded on the Moon; (7) the indigenous noble gas content of the Moon; and (8) characteristics and origins of organic species in the lunar regolith. Many of these science goals will be fulfilled through observations made from a variety of scales from atomic to planetary.
Investigating the stratigraphy and chronology of lunar landslide deposits to refine our understanding of lunar surface processes
Establishing a stratigraphy for the double drive tube provides an important context for other data collected from the core. For example, where do volatiles reside, and how are they distributed in the stratigraphy of the regolith? Furthermore, understanding the stratigraphy and chronology of lunar landslide deposits provides scientifically valuable information to understand (1) the regolith evolution processes active in the upper portion of a lunar landslide deposit; (2) important variables (e.g., temperature, volatiles) and their role in lunar landslide events; (3) triggers and chronology (e.g., impact events, activity along lunar scarps) for lunar landslide events; (4) dynamics of a lunar landslide deposit; (5) properties of the regolith that are important for the concentration and retention of lunar volatiles; and (6) identification of exotic South Massif rocks represented in the regolith.
Preparing for the collection and preservation of volatile-rich samples for future exploration
Future lunar missions will emphasize the appraisal of lunar volatile reservoirs and their in situ resource utilization potential. In situ analyses will provide information concerning undisturbed volatile reservoirs prior to sampling. For both in situ measurements and sampling, methods need to be designed that are cleaner and simpler than used for Apollo, and that disturb the soil less drastically. These CSVC samples represent our best chance to evaluate these approaches and to inform future missions on requirements for in situ measurements. Furthermore, they will provide engineering guidance for the design of future collection, containment, storage, and processing of lunar and solar system volatiles.
As the two CSVCs that were collected during the Apollo program were never opened, and no records exist for proposed strategies for opening these containers, ANGSA scientists and engineers have formulated strategies for gas extraction and sample handling. They are in the process of designing and testing gas extraction tools. Tools consist of an apparatus to pierce the thin wall at the base of the CSVC and release into the piercing chamber any volatile component without contaminating the enclosed regolith, along with a manifold to measure pressure and collect volatiles from the piercing tool collection chamber.
Opening Lunar Treasures
Thus far, JSC curation and ANGSA preliminary examination teams have extracted and are dissecting/examining the upper core sample from the double drive tube (73002). Prior to extraction and processing, the core was imaged using X-ray computed microtomography (XCT) through its aluminum drive tube container, which was doubly bagged in Teflon containers. The core was extracted from the drive tube on November 5, 2019, in a dry nitrogen core processing glove box by a curation team consisting of Charis Krysher, Andrea Mosie, and Juliane Gross (Fig. 5a–e). Following extrusion, the core was derinded (outer surface removed) and subsamples were collected and analyzed for organics and hydrogen isotopes. Following the derinding step the core will be dissected in 0.5-centimeter (0.2-inch) sections on three different passes (horizontal levels parallel to the length of the core). The 0.5-centimeter subsamples in pass 1 and 2 will be sieved to separate lithic fragments greater than 1 millimeter (0.04 inches). Following pass 3 the remaining core will be encased in epoxy and used to make continuous thin sections to examine the core stratigraphy. During the core dissection of pass 1, ANGSA preliminary examination team members (Fig. 5g) described and photographed both the core and the >1-millimeter lithic fragments (Fig. 5h). During each pass the core will be imaged using a multi-spectral analyzer that examined wavelengths comparable to those collected by orbital instruments on the Lunar Reconnaissance Orbiter (LRO), Kaguya, and Chandrayaan-1 (Fig. 5i) orbital missions. As of March 1, 2020, the first pass of the core had been processed. The gas phase in the CSVC will be documented, extracted, and analyzed during the winter of 2020–2021. The CSVC core will be imaged and extruded during the same period.
An overarching philosophy of the first lunar sample scientists to preserve samples for future generations, advanced analytical approaches, and future missions has already been demonstrated to be astute based on just the initial results by the ANGSA team. Twenty-first-century lunar missions such as LRO, Kaguya, and Chandrayaan-1 have placed the core within the context of regional and planetary geology and new important lunar concepts (e.g., volatile cycles and reservoirs on airless bodies, fault scarps, in situ resource utilization). The participation of a new generation of lunar scientists in the preliminary examination of core sample 73002 has linked them to the Apollo generation and prepared them for Artemis.
Some of the first data derived from 73002 was from XCT imaging of the core and lithic fragments, preliminary examination descriptions, multi-spectral imaging of the core, and sample measurements that could potentially be disturbed by sample processing over a period of time (volatile organics and hydrogen and its isotopic composition). Figure 6a illustrates the significant difference in resolution and clarity of the computed microtomography image compared to an X-ray scan taken in 1974. In addition to this higher resolution and clarity, the XCT imaging has numerous other advantages. Many thousands of image slices can be made through the core, making it transparent. This imaging enables a better strategy for core dissection; provides texture, compositional, and mineralogical information for lithic and mineral fragments (Fig. 6b); and allows the construction of stratigraphy based on grain size analysis. A video of X-ray slices through the 73002 core can be viewed at https://www.nasa.gov/feature/nasa-opens-previously-unopened-apollo-sample-ahead-of-artemis-missions.
The team at the NASA Goddard Astrobiology Analytical Laboratory received one of the early subsamples from the base of the 73002 core. Their aim was to uncover the origin and distribution of amino acids and their volatile precursors in lunar samples, as well as curation effects on these compounds. In addition to this first core sample, they will examine amino acids and their volatile precursors from core samples from varying depths, samples collected from shadowed and unshadowed environment on the lunar surface, samples stored in the CSVC (73001) versus the upper drive tube (73002), and samples stored frozen versus standard curation. The results on the upper drive tube core and witness plates will provide insights into handling and curation of the core sample in the CSVC.
The University of New Mexico stable isotope group received a sample from the upper portion of core sample 73002 for the measurement of hydrogen and its isotopic composition, chlorine isotopes, and oxygen isotopes. The isotopic composition of these elements provides a fingerprint of the sources for these volatile elements. For example, the hydrogen isotopic composition of the regolith identifies the contribution of hydrogen from the solar wind, lunar interior, cold traps, and potential terrestrial alteration. To eliminate the latter, these samples were processed in dry nitrogen gloveboxes at the JSC and the University of New Mexico and analyzed without the sample “seeing” any terrestrial hydrogen.
The University of Hawaii group brought a multispectral imager to the JSC lunar lab and carried out measurements on the core from outside the core processing cabinet. These measurements were made at a variety of wavelengths on analogous instruments on lunar orbital spacecrafts (LRO, Kaguya, and Chandrayaan-1). The measurements were designed to provide a variety of views of the core stratigraphy without terrestrial contamination.
The results of these initial analyses will be released during future science meetings (e.g., the 52nd Lunar and Planetary Conference, American Geophysical Union fall meeting, etc.).
These are the first measurements made during this three-year ANGSA team study. Other team members with establish the chronology and stratigraphy of the landslide deposit to deduce the triggers for these events, identify the distribution and characteristics of lunar volatiles in the core at the nanometer scale, examine how volatile elements behave on the lunar surface using a battery of stable isotopes that are sensitive to lunar processes, and recognize new lunar samples that will further the understanding of the past and current Moon. Ultimately, these measurements and observations are linked to the Artemis program and the future of humans on the Moon. Are there resources that can support human science, exploration, and economic activities between Earth and the Moon, on the lunar surface, and beyond the Moon? How are these resources identified, sampled, and processed? The answers to these and other questions will provide the foundation for how humans will explore our solar system in the future.