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Photo: Scientists Estimate Moon’s Finsen Crater is 3.5 Billion Years Old

A team of researchers led by a Chinese Academy of Sciences (CAS) professor determined that the absolute model age (AMA), or geologic age, of the Finsen crater on the moon’s far side is around 3.5 billion years.

A new study to be published in the January 2021 edition of planetary science journal Icarus estimated the AMA crater degradation rate of the lunar Finsen crater.

The team, led by CAS Prof. Di Kaichang, of the State Key Laboratory of Remote Sensing Sciences, Aerospace Information Research Institute, relied on information obtained by China’s Chang’e-4 probe, which landed on the far side of the moon on January 3, 2019.

A CAS memo republished by Phys.org on Friday revealed that the team used a digital orthophoto map and digital elevation model data produced by the Chang’e-4 probe to outline a flat and homogeneous area on the Finsen crater’s floor that was later used to manually map out craters nearby.

Chinese Academy of Sciences
Context map of Chang’e-4 landing site.

Scientists calculated the AMA of the Finsen crater by “fitting the obtained crater size-frequency distribution (CSFD) to standard lunar cratering chronology,” the release stated.

“Both cumulative and differential fits revealed an AMA of ~3.5 Ga [billion years], indicating Finsen crater was Imbrium-aged.”

The crater degradation rate at Finsen, calculated by current depth of the 25 largest craters in the defined area, was found to be around 21 ± 3 meters per billion years.

Comparatively, “however, the rate is much slower than that on other airless rocky bodies, for example, average degradation rate on [the asteroid] Vesta is 350 m/Gyr [billion years], and on [the asteroid] Gaspra is 100-1000 m/Gyr. One of the most likely reasons is that craters on asteroids are easily degraded or even erased by mass movements caused by impact-induced global seismic shaking.”

The growth rate of the regolith – the loose layer of dust and rock fragments that sits atop solid rock – at the Chang’e-4 probe landing site was also calculated to be about 3.4 meters per billion years. As solid rock breaks and wears away, the regolith increases in depth.

The release detailed that the regolith growth rate at the Chang’e-4 probe landing site is greater than that of almost all Apollo mission landing sites – except that of Apollo 16. The release highlighted that this could mean there is “a low weathering resistivity of Finsen crater ejecta to the harsh space environment.”

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