Level 1 — Absolute Beginner

A NASA spacecraft goes around the Moon. It takes many pictures.

A scientist looked at the pictures. He saw a bright spot. The spot was not there before.

It was a new hole in the ground. We call this hole a crater. It is 728 feet wide. That is as long as two football fields.

A big rock hit the Moon in 2024. The rock made the hole. This happens only about once in a hundred years.

Moon

The large round object that goes around the Earth.

crater

A big round hole in the ground made when something hits it.

rock

A hard piece of stone.

picture

An image that shows what something looks like.

scientist

A person who studies how the world works.

wide

Measuring a lot from one side to the other side.

hole

An empty space in a surface.

hit

To touch something hard and fast.

Level 2 — Elementary

NASA's Lunar Reconnaissance Orbiter has been circling the Moon since 2009, photographing the surface again and again. Robert Wagner, a scientist working with the mission, was scanning a large map built from those images when he noticed an unusually bright patch surrounded by a dark halo.

He compared pictures taken before and after. The bright patch was new. It marked a crater 728 feet across and 141 feet deep, wide enough to hold two football fields end to end and tall enough inside to stack three school buses one on top of another.

The impact happened on the eastern edge of the Moon at some point between 11 April and 22 May 2024. The object that struck was roughly the size of a building three to six storeys high, and it was either a comet or an asteroid.

The crater has been named McGetchin, after the lunar scientist Tom McGetchin. It is the largest newly formed crater ever identified in the solar system, and scientists estimate that an impact of this size hits the Moon only about once a century.

orbiter

A spacecraft that travels in a circle around a planet or moon.

surface

The outer layer or top of something.

halo

A ring of light or colour around an object.

impact

The moment when one object strikes another.

comet

An icy body in space that grows a tail near the Sun.

asteroid

A rocky object in space, smaller than a planet.

storey

One floor or level of a building.

century

A period of one hundred years.

Level 3 — Intermediate

Discoveries in planetary science are not always made by pointing a new instrument at the sky. Sometimes they are made by looking carefully at data that has been sitting in an archive. Robert Wagner, a scientist attached to NASA's Lunar Reconnaissance Orbiter, was working through a vast composite map of the lunar surface when an anomaly caught his attention: an unusually bright patch encircled by a dark halo, in a place where earlier images showed nothing of the kind.

Before and after comparison confirmed the reading. A crater 728 feet wide and 141 feet deep had been excavated on the eastern limb of the Moon between 11 April and 22 May 2024, and nobody had noticed for close to two years. The impactor is estimated to have been a comet or asteroid comparable in size to a building of three to six storeys, and the resulting structure is the largest freshly formed crater ever identified anywhere in the solar system.

The bright and dark pattern that gave the crater away is itself the evidence. An impact of this magnitude throws out ejecta that blankets the surrounding terrain in freshly exposed material, which reflects sunlight differently from the surface that has been weathered by micrometeorites and radiation over millions of years. The disturbed zone extends about four miles across, and because loosened soil holds heat poorly, it now runs roughly 16 degrees Fahrenheit cooler at night than the ground around it.

The crater has been named McGetchin, honouring the lunar scientist Tom McGetchin. Beyond the record, the finding has practical value. Events of this scale are thought to occur on the Moon roughly once a century, and knowing how often they happen, and what they do to the surface, matters for any programme planning to keep people or equipment on the Moon for extended periods.

archive

A collection of records or data kept for future reference.

anomaly

Something that differs from what is normal or expected.

limb

The visible outer edge of the disc of a moon, planet or star.

impactor

The object that strikes a surface and forms a crater.

ejecta

Material thrown out from a crater by an impact.

terrain

An area of land considered in terms of its physical features.

weathered

Changed over time by exposure to the environment.

micrometeorite

A tiny particle from space that strikes a surface.

Level 4 — Advanced

The Lunar Reconnaissance Orbiter has been returning imagery since 2009, and the cumulative archive it has produced is now large enough that its most valuable contents are not necessarily the frames anyone requested. Robert Wagner, a scientist working with the mission, was examining a composite lunar map when he registered an anomaly of a familiar type but unfamiliar scale: a conspicuously high albedo patch ringed by a darker annulus, occupying terrain that earlier coverage showed as unremarkable. Temporal comparison settled the matter. The feature postdated the previous pass.

The resulting measurements are the reason the find carries a superlative. The depression is 728 feet in diameter and 141 feet deep, and it formed on the Moon's eastern limb within a window bounded by 11 April and 22 May 2024, making it the largest newly formed crater catalogued anywhere in the solar system. The impactor is inferred to have been a comet or asteroid of dimensions comparable to a three to six storey structure, which is modest by the standards of planetary defence and substantial by the standards of ongoing lunar bombardment.

The photometric signature that betrayed the event is diagnostic rather than incidental. Hypervelocity impact excavates and redistributes regolith, mantling the surroundings in material that has not yet accumulated the optical maturity imparted by prolonged micrometeorite gardening and solar wind exposure. That immaturity manifests as elevated reflectance, while the concentric darkening traces a distinct emplacement regime within the ejecta blanket. Thermal data corroborates the interpretation: across a disturbed zone roughly four miles in extent, nocturnal temperatures run about 16 degrees Fahrenheit below the surrounding terrain, consistent with loosely consolidated material of reduced thermal inertia.

Designated McGetchin after the lunar scientist Tom McGetchin, the crater supplies an empirical anchor to a quantity that has been estimated more often than observed. Impacts of this magnitude are thought to occur on the Moon on the order of once per century, but the flux at the upper end of the size distribution is constrained by very few directly witnessed events. As agencies advance proposals for sustained surface presence, the practical question shifts from whether such strikes occur to how confidently their frequency and ejecta reach can be bounded, and a single well-characterised modern example does disproportionate work in that calculation.

albedo

The proportion of light a surface reflects.

annulus

A ring-shaped area between two circles.

postdate

To occur later in time than something else.

regolith

The layer of loose dust and broken rock covering solid bedrock.

optical maturity

The degree to which space exposure has darkened and altered a surface.

reflectance