Scientists Identify Rare Once-in-a-Century Impact Crater on the Moon

Sometime in the spring of 2024, a space rock traveling at extraordinary speed slammed into the lunar surface. It carved out a funnel-shaped hole 225 meters wide and 43 meters deep — large enough to swallow a 15-story building [1]. The ejecta, rock and dust blasted outward by the collision, scattered debris detectable up to 120 kilometers from the impact site [2]. The largest ejected boulder measured roughly 13 meters across [1].

No one saw it happen.

The crater went undetected until planetary scientist Mark Robinson, principal investigator of NASA's Lunar Reconnaissance Orbiter Camera (LROC), identified it while comparing orbital images taken before and after the event. He presented the findings at the 57th Lunar and Planetary Science Conference on March 17, 2026 [3][4].

The Largest Crater in LRO's History

Since NASA's Lunar Reconnaissance Orbiter entered lunar orbit in 2009, scientists have catalogued hundreds of new craters by comparing "temporal pairs" — images of the same patch of terrain taken at different times [5]. The previous record-holder was a 70-meter crater, itself a notable find [1]. This new feature is more than three times that diameter.

The crater sits in the lunar highlands, where the impact punched through layers of regolith into harder volcanic rock beneath. The elongated shape of the cavity and the steep angle of its walls indicate the impactor arrived from the south-southwest, scattering debris northward in what Robinson's team described as a "distinctive tongue-shaped pattern" [2]. Inside the crater, researchers found patches of unusually dark material — almost certainly glassy rock, flash-melted by the heat of impact and instantly solidified [1].

What distinguishes this from most lunar craters is the quality of the before-and-after record. For the first time, scientists have meter-scale photographs of a crater this size captured both before and after formation, providing an unprecedented dataset for studying impact mechanics [1][6].

Statistical Rarity: A Once-in-139-Year Event

According to crater production models — mathematical frameworks that estimate how frequently impacts of a given size occur — a crater of this magnitude should form somewhere on the Moon only once every 139 years [1][4]. The models are calibrated against the known population of craters across the lunar surface and the estimated flux of impactors in near-Earth space.

That statistical rarity does not mean the event was unexpected in an absolute sense. The Moon's surface area is about 38 million square kilometers. At any given square kilometer, the wait time between major impacts stretches into centuries. But across the entire surface, smaller impacts happen constantly, and even large ones occur with regularity over geological timescales.

For context, asteroids with a 1-kilometer diameter strike Earth roughly every 500,000 years [7]. Impacts at the scale that formed Arizona's Meteor Crater — roughly 20 megatons of energy — occur approximately every 50,000 years [7]. The object that struck the Moon was far smaller than either benchmark, but the absence of any atmosphere meant the full kinetic energy transferred directly into the surface.

What the Crater Reveals About the Impactor

Robinson's team has not published a definitive estimate of the impactor's mass or diameter, though the abstract presented at LPSC 2026 documented the crater's dimensions and ejecta pattern in detail [3]. Standard scaling laws for lunar impacts — which relate crater diameter to impactor size, velocity, and density — suggest the object was likely a few meters across, traveling at typical meteoroid velocities of 20–30 kilometers per second.

The composition of the flash-melted glass inside the crater may eventually help determine whether the impactor was an ordinary chondrite (a stony asteroid fragment), a carbonaceous body, or cometary material. That classification matters because it feeds into population models maintained by NASA's Center for Near Earth Object Studies (CNEOS), which tracks and computes orbits for all known near-Earth objects [8]. As of 2025, more than 36,000 NEOs had been catalogued [8], but the vast majority of objects in the size range capable of producing a 225-meter lunar crater remain undetected.

Source: NASA CNEOS

Data as of Apr 1, 2025CSV

The Detection Gap

The fact that a crater of this size went unnoticed for nearly two years raises questions about monitoring infrastructure. NASA's Lunar Impact Monitoring Program, operated by the Meteoroid Environment Office at Marshall Space Flight Center, uses ground-based telescopes to watch for impact flashes on the Moon's night side approximately 10 nights per month [9]. In 2025, the program's Automated Lunar and Meteor Observatory (ALaMO) underwent a major upgrade, installing four new cameras linked to the Global Meteor Network's roughly 1,300 cameras worldwide [9].

But ground-based flash monitoring has inherent limitations. It can only observe the Moon's Earth-facing hemisphere, and only during the narrow windows when the night side is visible from Earth. An impact on the far side, or one occurring during lunar daytime, will produce no observable flash from Earth. The spring 2024 impact appears to have fallen into one of these blind spots.

The LRO itself is not a real-time monitoring system. It photographs lunar terrain over successive orbits, building up coverage gradually. The time lag between an impact and its detection through temporal pair analysis depends entirely on when the orbiter next photographs that specific location — a process that can take months or years [5].

Compare this to Earth-facing planetary defense: CNEOS and its partner networks can detect and compute the orbit of an incoming object within hours of initial observation, issuing automated alerts through the International Asteroid Warning Network (IAWN) [10]. For the Moon, no equivalent real-time warning system exists.

Planetary Defense Budget: Growing but Focused on Earth

NASA's Planetary Defense Coordination Office (PDCO), established in 2016, has seen its budget grow from $5.8 million in 2010 to $341 million in the fiscal year 2026 appropriation [11][12]. The bulk of recent funding — $300 million in the Senate-passed FY2026 budget — goes to the NEO Surveyor mission, a space-based infrared telescope designed to find 90% of near-Earth objects 140 meters or larger within 10 to 12 years of operation [12].

Source: The Planetary Society

Data as of Jan 1, 2026CSV

That mandate originated from a congressional directive that initially set a 2020 deadline — a target that was always impossible to meet with ground-based telescopes alone [11]. As of 2019, only 40% of hazardous asteroids at or above the 140-meter threshold had been discovered [11]. NEO Surveyor aims to close that gap, but its focus is squarely on Earth-threatening objects, not lunar monitoring.

The 2022 DART mission demonstrated that a spacecraft can alter an asteroid's orbit, successfully changing the trajectory of the moonlet Dimorphos around the larger asteroid Didymos [10]. That proof of concept, however, addressed deflection — not detection. The gap exposed by the lunar crater discovery is on the detection side: objects in the few-meters size range remain largely invisible to current survey systems until they are very close to impact.

What This Means for Artemis and Lunar Habitation

NASA has identified nine candidate landing regions near the lunar south pole for Artemis III, the first crewed landing mission since Apollo 17 [13]. Site selection criteria include surface visibility, sunlight exposure, proximity to permanently shadowed regions (which may contain water ice), and geological diversity [13]. Impact ejecta is already a factor in these assessments — researchers model ejecta thickness and layering at each candidate site to understand what materials astronauts might encounter [14].

The 225-meter crater adds a specific data point to that risk calculus. The disturbance zone extending 120 kilometers from the impact site means ejecta from a single event can affect terrain far beyond the crater itself [2]. On the airless Moon, ejected fragments travel ballistically at high velocity with no atmospheric drag to slow them.

A 2005 NASA study estimated only a 1% probability of a damaging impact on any single structure during a lunar mission, but noted that this risk increases by 1% with each additional structure placed on the surface [4]. Robinson and colleagues have argued that "additional precautions should be taken to minimize or eliminate potential structural damage from falling objects" as the scope of human presence on the Moon expands [4].

For near-term Artemis missions — short-duration surface stays — the statistical probability of a direct strike remains very low. But for the longer-term vision of sustained habitation, including the planned Gateway station in lunar orbit and surface infrastructure, impact shielding and hazard protocols become engineering requirements rather than theoretical concerns.

The Case Against Alarm

Several researchers have cautioned against overstating the significance of this crater. The event, while visually striking in before-and-after imagery, falls well within the range predicted by existing cratering models. A once-in-139-year event is not a once-in-a-millennium surprise — it is a statistical expectation that happened to be captured with good imaging for the first time [1].

The impact carries no meaningful update to Earth's risk assessment. The Torino Scale, which rates the hazard posed by near-Earth objects on a 0-to-10 scale, classifies objects of this size as posing no significant threat. An impactor a few meters across would almost certainly burn up in Earth's atmosphere or, if it survived to the surface, produce only localized damage — well below the threshold of regional or global consequence [7].

The Moon, with its 38 million square kilometers of unoccupied surface, absorbs impacts constantly. What changed with this discovery is not the frequency of impacts but the ability to document one at high resolution. As Robinson's team emphasized, the scientific value lies in the unprecedented before-and-after dataset, not in any revision to impact hazard estimates [6].

Academic Interest and Research Momentum

Research on lunar impact cratering has grown substantially over the past decade. Academic publications on the topic peaked at 1,176 papers in 2024, up from 344 in 2011 — a more than threefold increase driven by LRO data availability, automated crater detection algorithms, and renewed interest in lunar surface science ahead of Artemis [15].

Source: OpenAlex

Data as of Jan 1, 2026CSV

Legal Frameworks: The Outer Space Treaty and Its Limits

If an object of comparable size were detected on a collision course with Earth rather than the Moon, the international response framework would be thin. The 1967 Outer Space Treaty, signed by 114 nations, prohibits the placement of nuclear weapons in space but is largely silent on planetary defense operations [16]. Legal experts have noted that the treaty's language could be interpreted as banning nuclear deflection devices — even those intended purely for planetary defense — because it does not distinguish between weapons and defensive tools [16].

The UN Office for Outer Space Affairs (UNOOSA) coordinates planetary defense discussions through two advisory bodies: the International Asteroid Warning Network (IAWN), which handles detection and notification, and the Space Missions Planning Advisory Group (SMPAG), which develops cooperative mitigation plans [10][16]. Neither body has enforcement authority or its own operational assets. In practice, only NASA (through PDCO and DART's successor programs) and ESA (through its Hera follow-up mission to Dimorphos) maintain active deflection research programs.

UNOOSA has designated 2029 as the International Year of Planetary Defence and Asteroid Awareness, timed to coincide with the close flyby of asteroid Apophis — a 370-meter object that will pass within 31,000 kilometers of Earth [16]. That event will serve as a live exercise for detection and tracking systems worldwide, but it arrives against a backdrop of legal ambiguity about who has authority to act if deflection becomes necessary.

No nation currently maintains a ready-to-launch intercept capability for an Earth-bound asteroid. The DART mission took years to develop and deploy. A confirmed threat with short warning time — weeks or months rather than years — would find the international community without a tested rapid-response option.

What Comes Next

The 225-meter crater will become one of the most studied features on the Moon. Its high-resolution before-and-after imagery provides ground truth for testing impact models that have, until now, been calibrated primarily against decades-old experimental data and computer simulations [6]. The glassy melt deposits inside the crater offer a window into impact physics at energies difficult to replicate in laboratories.

For planetary defense, the crater is a reminder that detection remains the weakest link. The NEO population below 140 meters is poorly characterized, and objects in the few-meters range — capable of producing craters hundreds of meters wide on the Moon — are effectively invisible until they are days from impact with Earth [11]. The Moon itself, pockmarked and unshielded, serves as a continuous natural experiment in what happens when those objects arrive unannounced.