Moon's Largest Impact Crater May Have Scattered Rare Materials Across Artemis Landing Zone

Roughly 4.3 billion years ago, a 260-kilometer-wide asteroid — one that had already differentiated into a dense iron core and rocky mantle — slammed into the Moon's far side on a north-to-south trajectory at approximately 13 kilometers per second [1][2]. The collision excavated a basin more than 2,500 kilometers across and up to 8.2 kilometers deep, making the South Pole-Aitken (SPA) Basin the largest confirmed impact structure on the Moon and one of the largest in the solar system [3]. Only the Borealis Basin on Mars, whose existence remains debated, may be larger.

What makes this ancient wound newly consequential is a pair of studies published in 2025 and 2026 that have overturned longstanding assumptions about the impact's geometry — and, in doing so, placed the richest deposits of deep lunar material squarely within the zone where NASA's Artemis astronauts are scheduled to land.

A Decapitated Asteroid and a Revised Trajectory

For decades, planetary scientists assumed the SPA-forming impactor struck from the south. Two recent studies have reversed that conclusion. Research led by Jeffrey Andrews-Hanna at the University of Arizona, published in Nature in October 2025, demonstrated that the basin's teardrop shape — narrowing toward the south — is diagnostic of a northward origin [2][4]. "These enormous craters narrow in the direction the impactor was traveling, forming a shape similar to a teardrop or avocado," Andrews-Hanna explained [4].

A complementary study led by Shigeru Wakita of Purdue University, published in Science Advances in May 2026, modeled the impactor as a differentiated body whose iron core and silicate mantle separated during the collision — effectively a "decapitated" asteroid [1]. Wakita's simulations pinpointed an impact velocity of roughly 13 km/s, consistent with an object on a low-inclination, Earth-like orbit that likely originated from the Mars zone during early solar system formation [1].

The trajectory reversal carries a major practical implication. In basin-forming impacts, the bulk of excavated material is flung downrange — in the direction the impactor was traveling. A north-to-south trajectory means the densest concentration of deep ejecta landed on the basin's southern rim. That rim is the lunar south pole — exactly where Artemis III is headed.

What the Impact Dug Up

The SPA impact excavated to depths exceeding 100 kilometers, breaching the primordial lunar crust and penetrating the upper mantle [5][6]. Modeling estimates suggest the ejecta blanket contains more than five million cubic kilometers of mantle-derived material [3]. According to Wakita's simulations, mantle ejecta was distributed approximately 550 kilometers beyond the rim in the downrange (southward) direction and 650 kilometers in the cross-range direction, with no mantle ejecta appearing uprange [1].

The composition of this material is scientifically significant. Orbital spectroscopy indicates that SPA ejecta is enriched in low-calcium pyroxene with magnesium numbers (Mg#) of 85 or higher, consistent with a post-overturn upper mantle dominated by orthopyroxenite [5][6]. The western ejecta blanket also shows elevated concentrations of radioactive thorium — a signature of KREEP (potassium, rare-earth elements, and phosphorus), the residual liquid from the Moon's primordial magma ocean [4][7].

Andrews-Hanna's team proposed that the impact breached a boundary between ordinary far-side crust and a KREEP-enriched magma ocean layer that had been squeezed toward the near side as the far-side crust thickened. The asymmetric thorium distribution — concentrated on the basin's western flank but absent from the east — supports this model [4].

Chang'e-6: A Preview From the Far Side

China's Chang'e-6 mission provided the first ground-truth test of these orbital predictions. In June 2024, the spacecraft returned 1,935.3 grams of material from the Apollo Basin, a smaller crater within SPA — the first samples ever collected from the Moon's far side [8].

Analysis of the samples confirmed several predictions. Highly magnesian olivines (forsterite numbers from 86.8 to 95.6) were identified, with the most primitive, nickel-rich grains interpreted as fragments of the lunar primitive mantle [9]. The crystallization sequence observed in Chang'e-6 norites was most consistent with an orthopyroxene-dominated mantle source mixed with 20–30% highland crustal material [10]. Basalt fragments dated to 2.83 billion years ago showed extreme depletion in strontium and neodymium, pointing to an ultra-depleted mantle source shaped by magma ocean crystallization [11].

These results validate — at least partially — the hypothesis that SPA ejecta preserves mantle signatures. But they also reveal the complexity of the picture: about 90% of material in the top meter of regolith at the Chang'e-6 site was local mare basalt, not foreign ejecta, a consequence of billions of years of impact gardening [8].

Artemis Landing Sites and the Ejecta Zone

NASA has identified 13 candidate landing regions near the lunar south pole for Artemis III, each approximately 15 by 15 kilometers [12]. All 13 regions fall within or adjacent to the modeled SPA ejecta dispersal zone. A 2024 multi-criteria analysis evaluated 1,247 potential locations within these regions using six criteria: surface visibility, astronaut line-of-sight, proximity to permanently shadowed regions (PSRs), solar illumination, Earth communication access, and geological diversity including mafic mineral abundance [13].

Source: Evaluating Potential Landing Sites for Artemis III (Boazman et al. 2024)

Data as of Dec 1, 2024CSV

Site DM2, on the rim of Nobile crater (84°12'S, 60°42'E), scored highest across sensitivity analyses. Of the top 100 candidate locations, 36% fell within DM2 and 30% within Site 23 [13]. The study found that scientific and safety objectives generally aligned rather than conflicted — a result that tempers the narrative of science being sacrificed for operational convenience.

All candidate sites require continuous solar access for a 6.5-day surface stay, which restricts landing to topographically elevated positions — ridges and crater rims — that happen to be the same landforms where SPA ejecta would have preferentially accumulated [12]. This is a geological coincidence that works in science's favor.

The Decadal Survey's Verdict

The planetary science community has been explicit about the scientific value of SPA samples. The most recent Planetary Science Decadal Survey (Origins, Worlds, and Life, 2023–2032) identified an SPA sample return as the highest priority strategic mission for NASA's Lunar Discovery and Exploration Program — a designation the basin has held across three consecutive decadal surveys [14].

The recommended implementation, a mission concept called Endurance-A, would use a long-range rover to traverse diverse terrains within SPA, collect approximately 100 kilograms of samples, and deliver them to a location where astronauts could retrieve and return them to Earth [14]. This architecture depends on Artemis crew being present in the south polar region — reinforcing the scientific case for the chosen landing zone.

Source: OpenAlex

Data as of Jan 1, 2026CSV

Academic interest in the SPA basin has surged in parallel with Artemis planning. Research publications referencing the lunar south pole and SPA basin reached 165 papers in 2025, up from 62 in 2019 [15]. The trajectory reflects both the approaching Artemis timeline and the influx of Chang'e-6 data.

The Skeptic's Case: Impact Gardening and the Regolith Problem

Not all planetary scientists share equal confidence that Artemis surface sampling will recover pristine mantle material. The core challenge is time. Over 4.3 billion years, the lunar surface has been relentlessly reworked by subsequent impacts — a process called impact gardening — and subjected to space weathering from solar wind and micrometeorite bombardment [5][6].

The Chang'e-6 results illustrate the problem quantitatively. In the top meter of regolith at the Apollo Basin site, local intermediate-titanium mare basalt dominated the sample, with roughly 90% of drilled material originating from local sources within the upper 1 to 60 meters [8]. The SPA ejecta signal, while detectable, was diluted.

At the Artemis landing sites, the situation may be more favorable — the south polar region lacks extensive mare basalt flooding, so SPA ejecta should constitute a larger fraction of the surface material. A 2025 study in the Journal of Geophysical Research examined "impact resurfacing" in the Artemis exploration zone and found that the most pristine exposures of thorium-bearing SPA ejecta have been excavated from depth by subsequent smaller impacts, creating fresh windows into the buried ejecta blanket [16]. The implication: astronauts may need to target specific small, young craters that have punched through the reworked surface layer to access less-degraded material.

But even fresh exposures are not unambiguous. The compositional and mineralogical signatures of the original ejecta deposit have been diluted at the surface by the mixing of local and nonlocal materials over geologic time [6][16]. Whether Artemis astronauts can collect samples that planetary scientists can confidently attribute to the SPA impact — as opposed to reworked regolith — remains an open question that sample return and laboratory analysis will need to resolve.

Commercially Valuable Materials: Legal Reality and Physical Uncertainty

Reports linking SPA ejecta to commercially valuable resources — platinum-group elements, helium-3, rare earths — require careful qualification. The thorium enrichment detected in SPA ejecta reflects KREEP concentrations, which do contain rare-earth elements, but at abundances measured in parts per million, not economically extractable grades by any current technology [4][7].

Helium-3, implanted in the lunar regolith by solar wind, is present across the entire Moon and is not specific to SPA ejecta. Platinum-group elements are associated with meteoritic contamination in the regolith rather than excavated mantle material [3].

The legal framework for any future extraction is defined by the 1967 Outer Space Treaty, which prohibits national sovereignty claims over celestial bodies, and the Artemis Accords, signed by 67 nations as of May 2026 [17][18]. The Accords adopt the U.S. interpretation that while no nation can claim sovereignty over the Moon, a nation or private entity can own, use, and sell resources it extracts — a position that does not expressly declare extraction legal but states it would not constitute national appropriation [18]. China and Russia are not signatories and have advanced their own International Lunar Research Station program, creating a parallel framework that has not endorsed the Accords' resource-use provisions [17].

No nation or private entity has formally staked a territorial claim to the lunar south pole — doing so would violate the Outer Space Treaty. But the concentration of mission hardware and landing plans in the same narrow band of lunar real estate has created a de facto competition for physical access that existing legal instruments were not designed to adjudicate [18].

EVA Risks in the Ejecta Zone

The lunar south pole's topography presents specific operational hazards. Slopes in the region frequently exceed 15 degrees, the operational safety threshold for Artemis EVAs [19][20]. More challenging traverses may require astronauts to negotiate slopes up to 20 degrees at distances up to 2 kilometers from the landing site [19].

Permanently shadowed regions — the same areas targeted for water ice prospecting — pose distinct power and thermal risks. A 2026 accessibility assessment of 31 priority PSRs found substantial heterogeneity, with median path lengths to PSR interiors ranging from 12 to 50 kilometers and minimum round-trip mechanical energy costs spanning an order of magnitude, from 0.4 to 4.4 kilowatt-hours [20]. Solar-powered rovers face hard constraints: venturing into permanent shadow requires stored energy sufficient for the entire round trip, plus safety margins for navigation errors [21].

If mission planners prioritize geological traverses toward high-interest ejecta exposures — particularly fresh craters that may have excavated SPA material from beneath the regolith — the EVA profile becomes more demanding. These targets are not necessarily co-located with the safest or most power-favorable terrain. A 2023 study on astronaut traverse optimization found that 20 PSRs were accessible from the top-ranked landing sites with slopes under 10 degrees, but only a subset of those paths would also intersect geologically interesting ejecta deposits [19].

The tension is real but manageable. Mission designers have the orbital data to identify traverses that balance geological interest with safety margins. The question is whether the 6.5-day surface timeline for Artemis III — essentially a sprint mission — allows enough flexibility to pursue both water ice and deep mantle ejecta objectives, or whether one will be subordinated to the other.

What Artemis Could Settle

The scientific stakes are unusually clear. SPA samples could resolve the age of the basin — and with it, the timing of the Late Heavy Bombardment, a hypothesized period of intense cratering that shaped the inner solar system [14]. They could reveal the composition of the Moon's upper mantle, testing models of how the lunar magma ocean crystallized and overturned [10][11]. They could confirm or refute the hypothesis that KREEP was asymmetrically distributed by the impact, reshaping understanding of why the Moon's near and far sides differ so dramatically [4].

These are not abstract academic questions. The Moon is the most accessible record of conditions in the inner solar system during the first billion years — a period for which Earth's own geological record has been almost entirely destroyed by plate tectonics. Material excavated from 100 kilometers beneath the lunar surface and flung onto the south pole 4.3 billion years ago may preserve information about planetary formation that exists nowhere else within reach of human spacecraft.

Whether Artemis astronauts can actually recover that information from a surface that has spent four billion years being pummeled, irradiated, and churned is the central uncertainty. The Chang'e-6 results suggest the signal is there but attenuated. The orbital data says the right landing zone has been chosen. The rest depends on traverse planning, sample selection, and — as Andrews-Hanna put it — the "state-of-the-art facilities" waiting on Earth to analyze what comes back [4].