Extract from ABC News
The newly-discovered McGetchin crater spans about a kilometre. (Supplied: NASA Goddard/Intuitive Machines/Robert Wagner)
When NASA scientist Robert Wagner first noticed a "bright spot" on the surface of the Moon in 2025 he was unaware he had just discovered the largest, newly formed crater ever found in the solar system.
Measuring wider and about as deep as the Roman Colosseum, researchers believe the crater was formed after a powerful surface impact just over a year before humans noticed it.
Its discovery revealed an impact event NASA says only happens every 132 years, and which scientists hope will become critical to informing future research.
The Moon's newest crater measures about 43 metres deep. (Supplied: NASA Goddard/Intuitive Machines/Robert Wagner)
How was the Moon's newest crater found?
On October 24 last year Mr Wagner was examining routine data quality reports and maps generated from NASA's Lunar Reconnaissance Orbiter (LRO).
The LRO has circled the Moon for more than 17 years, mapping its topography, surface composition, temperature and radiation environment, NASA says.
Through its work, scientists are able to identify changes to the Moon's surface by comparing high-resolution "before and after" photographs taken by the LRO.
The discovery of the McGetchin crater revealed a lunar impact that scientists say only happens every 132 years. (Supplied: NASA Goddard/Intuitive Machines/Robert Wagner)
When Mr Wagner spotted "an unusually large bright spot circled by a dark halo", he said he immediately knew it needed further analysis.
"I just stopped, dropped everything, and started looking into what that spot was," he said.
"It was by far the most obvious impact debris pattern I've ever seen in one of these images."
The discovery became known as the McGetchin crater, named after pioneer lunar scientist Tom McGetchin.
It measures 222 metres across and 43 metres deep, which is three-times bigger than the previous record holder found by the LRO a decade ago.
A before-and-after view of the patch of the Moon's surface where the McGetchin crater was formed. (Supplied: NASA Goddard/Intuitive Machines/Robert Wagner)
Researchers say they believe the crater was formed between April 11 and May 22, 2024, as a result of a comet or asteroid strike the size of a three- to six-storey building.
The LRO's numerous crater discoveries since its launch in 2009 shows the top 2 centimetres of the Moon's surface soil is being overturned by ejected material every 80,000 years — faster than previously thought, scientists say.
Further checks exposed 'cold spot'
In addition to taking photographs of the Moon, the LRO also has instruments that pick up variations in temperature that can highlight shifts in the lunar surface.
In examining an area surrounding the McGetchin crater, researchers uncovered a 6.5km patch that was marginally cooler at night.
A "cold spot" surrounded the crater where unsettled Moon dust and soil was unable to retain surface heat. (Supplied: NASA Goddard/UCLA/JHU APL)
That happens because a surface impact unsettled the Moon's bedrock dust and soil, known as regolith, making it less dense and therefore less able to retain heat.
"The large extent of this 'cold spot' is striking, scientists say, because it shows that impacts can modify the Moon's surface far beyond the crater itself," NASA said in a blog post on its website.
"These physical changes could affect how rover wheels interact with the surface, for instance."
How often do Moon strikes happen?
NASA says that impacts involving "space rocks and other objects" on the Moon's surface happen reasonably frequently.
Pockmarked since ancient times, the moon bears some of the solar system's largest impact craters, including one that stretches more than 2,400km across.
About 140 new craters are identified across the lunar surface each year, according to the US space agency.
The McGetchin crater, indicated by a black arrow in an image showing the extent of other craters. (Supplied: NASA Goddard/Intuitive Machines/Robert Wagner)
Of those, most of them are caused by "microscopic projectiles" that create craters too small to be picked up by the LRO's photography.
But the spacecraft can still capture craters that measure about nine metres in width, at the smallest, made by rocks measuring just over a metre.
In assessing the images taken by the LRO's two cameras, scientists have been able to identify and map "landslides, landers, seismic faults and even hints of lava tubes", NASA said.
Researchers often analyse close-up images of small parts of the Moon's surface, but also occasionally look at wider-scale photos showing a larger area.
Mr Wagner said he spotted the McGetchin crater because NASA's LRO software flagged shifts in the lunar surface by highlighting them in different shades in the wide-scale before and after photos.
NASA said the process often picks up many "false alarms", and so Mr Wagner said he needed to verify the McGetchin discovery by looking for "small fuzzy halos around pixel‑wide bright points, which indicate splashes of regolith around a new crater".
His team then compared those wide-scale images to the close-up images taken of the same area which exposed the size, shape and surrounding terrain of the crater.
This latest impact churned the lunar surface for more than 100km, with dust and rocky soil hurled away at a higher angle than expected, according to Mark Robinson, a chief scientist for the LRO's cameras who works at Intuitive Machines.
Mr Robinson was the lead author for one of two studies that reported the LRO's new findings.
"This event constitutes a statistically rare, effectively once-in-a-lifetime observation," Mr Robinson's research team wrote in one of the studies.
ABC/AP
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