Much more to the moon

A recent study by Planetary Science Institute geologists suggests that the moon is more geologically active than previously thought.

Researchers have placed the moon’s age at close to two million years
Researchers have placed the moon’s age at close to two million years

The study, published in the journal Nature by geologists Peter Schulz and Carli Pieters, suggests that the moon may have seen eruptions of interior gasses as recently as one million years ago, challenging the conventional wisdom according to which it has not seen widespread volcanic activity for at least the last three billion years ago.

The study uses three distinct lines of evidence to support the assertion that volcanic gas has been released from the moon’s surface within the last one to 10 million years.

The researchers focussed on a D-shaped area called the Ina structure that was first recognised in images from Apollo missions. This structure indicates that gas releases may have exposed fresh surfaces on the moon. It also shows very few craters within the depression, and low-angle illumination reveals sharp features with little evidence of weathering.

Schultz says that the unusual sharpness of the features within the Ina structure was something that attracted his attention. He says that on Earth, wind and water quickly wear down freshly exposed surface features, and on the airless moon, constant bombardment with tiny space debris accomplishes a similar result.

"Something that razor-sharp shouldn’t stay around long. It ought to be destroyed within 50 million years," said Schulz.

By comparing the fine-scale surface features within the Ina structure to other areas on the moon with known ages, the researchers were able to place its age at closer to two million years.

The second evidence for the feature’s relative youth is established by the scarcity of asteroid impact craters on the surface within the Ina structure. The researchers identified only two clear impact craters larger than 30 metres on the 8 sq km of the structure’s floor. This frequency is about the same as at South Ray Crater, near the Apollo 16 landing site.

Lunar scientists studying them have also the surface material ejected from South Ray Crater have agreed on a date of approximately two million years, based on cosmic ray exposure.

The third piece of support for the authors’ hypothesis comes from comparing the spectral signatures of deposits in the Ina depression to those from very fresh craters. As lunar surface deposits weather, the wavelengths of light they reflect change in predictable ways.

Overall reflectance gets less bright, and the ratio of light at 1,000 nm wavelengths to 750 nm wavelengths increases. Based on these colour ratios, the deposits on Ina’s floor are exceptionally young, and possibly even newly exposed.

The authors say that the appearance of the surface at Ina does not indicate an explosive release of magma, which suggests a rapid release of gasses from the surface deposits.

The authors conclude that the only sure way to resolve the question whether the moon is more geologically active than previously thought, would be to collect samples at such sites.

"Ina and other similar features are great targets for future exploration, by people or robots. "They might be the best place to get a good look at the interface between the powdery regolith and the consolidated rock beneath," said G. Jeffrey Taylor, a lunar researcher at the University of Hawaii. — ANI