Chandrayaan-1 may have just detected oldest impact basin on moon

For the first time, planetary scientists have confirmed the existence of a hidden impact crater on the lunar surface using mineralogical data obtained from Chandrayaan-1 and it could predate the oldest known impact craters on the moon.

A team of researchers from the Physical Research Laboratory (PRL), Ahmedabad, have identified the Australe Basin, which had remained untraced as this ancient basin had suffered erosion along its rims making it extremely difficult even for modern-day imaging techniques to detect.

Scientists believe that there are approximately 300 impact basins present on the moon. Of these, only 74 have been detected so far. Impact basins are formed over the lunar surface due to various violent space activities, like asteroid or meteorite hits.

These are large craters, often several hundreds of kilometres in diameters, and can have distinct outer rims. Due to the space hits, these craters are often found with remnants of volcanic activities. This new study, published in the The Planetary Science Journal, has now shed light on one such impact basin confirmed to be located along the southeastern hemisphere of the moon.

It has distinct morphology and gravity signatures and some unique mineralogical compositions. PRL scientists are also of the opinion that this basin could well be older than and largest and the oldest known South Pole Aitken Basin (formed over 4 billion years ago) on the Moon.

Speaking with The Indian Express, Neha Panwar, planetary scientist and lead author of the study, said, “The volcanism inside the Australe Basin has a very unique mineralogy. Unlike the majority of basalts on the Moon that are high in calcium bearing, these basalts are relatively lower in calcium and higher in magnesium.” Moreover, the Australe Basin was found to be in a province characterized by 248 small basalt ponds arranged in a circular pattern unlike several of the previously known impact basins that are classified for their smooth and vast hardened lava surfaces.

There were 11 scientific payloads onboard the Chandrayaan-1. Of these, six were contributions from international space agencies including National Aeronautics Space Administration (NASA) and the European Space Agency. The mineralogy of the Australe Basin was detected using data gathered by the Moon Mineralogy Mapper of NASA.

It is an imaging spectrometer that was designed to create the mineralogical map of the lunar surface. It operates between the 405 and 3000 nanometer wavelength range. Scientists studied the absorption bands exhibited by some of the key lunar minerals, such as pyroxenes, olivine, and plagioclase.

The current study could offer detailed mineralogical insights of the region, particularly given the renewed interests shown by many countries with the proposed Moon Base mission by NASA and India’s Chandrayaan-4, a lunar sample return mission.

“This study provides us with a framework to interpret the data from the landing missions in the broader geological context, by studying the regions that could have contributed material to these landing sites. Such unique sites can be important targets for the future sample return missions,” she said.

PRL scientists noted that even the Chandrayaan-3 landing site, now known as the Shiv Shakti point, possessed higher concentrations of magnesium. And that could be linked to some material originally from the South Pole Aitken Basin to have gotten transported to the Shiv Shakti point, located approximately 350 kms apart.

“Interestingly, what we found was that the Australe region, too, has widespread Magnesium-bearing lithologies. Since the region lies close to the moon’s South Polar region, it is likely that the material excavated by this impact would also have been deposited across the South Pole.

With the future missions planned in the South Polar Region, it is important to understand how the regolith in these regions has evolved over billions of years,” she explained.