Did a massive impact around 4.3 billion years ago create the South Pole-Aitken (SPA) basin and threw up sulphur-rich material from the Moon’s primitive mantle? Probably yes, say scientists at the Physical Research Laboratory, an autonomous unit of India’s Department of Space.
The Ahmedabad-based laboratory reached its conclusions after analysing elemental data from Chandrayaan-3 at Shiv Shakti Point (69.37° S, 32.32° E), in the Moon’s southern high-latitude highlands.
What Chandrayaan-3 Revealed
As part of India’s third Moon mission, Chandrayaan-3, the Pragyan rover deployed the Alpha Particle X-ray Spectrometer (APXS) to measure the elemental composition of the Moon’s surface at an unexplored region. The APXS measurements of major elements also reinforced the theory of a lunar magma ocean (LMO) – that the Moon was once an ocean of molten rock, ISRO stated.
The APXS also measured abundances of volatile elements, including sodium, potassium, and sulphur in the highland soils. Scientists from the Physical Research Laboratory have made a detailed analysis of the abundances of these volatile elements.
Interestingly, sodium and potassium levels at the Chandrayaan-3 site were significantly lower than those in highland soil samples from earlier missions like Apollo 16 and Luna 20.
On the other hand, the concentration of sulphur was 300-500 ppm higher.
This stark difference in volatile element levels intrigued Indian scientists. They decided to go deeper to study the probable cause that led to their enrichment or depletion at the Chandrayaan-3 landing site.
Moon’s Early Mantle and SPA Basin Impact
According to the study published in the Nature Communications Earth and Environment journal, on the Moon, the Type I Carbonaceous chondrite (CC) meteorites crashing on the surface can add approximately 400-1000 ppm of sulphur to the soil.
However, this still falls short of explaining the 200–400 ppm excess in sulphur measured by APXS.
Moreover, the surface temperature observed at the landing site ranges between 250 and 300 K (Kelvin), which is much higher than the volatility temperature of sulphur.
In this case, the cold-trapping mechanism of surface enrichment of sulphur for geologically long periods is not possible at the landing site. Therefore, there has to be another source of sulphur that increased its concentration at the landing site.
As per the research paper, at the end of the lunar magma ocean (LMO) crystallisation stages, the residual molten layer became enriched in a mineral called Troilite (FeS).
According to the scientists at the Physical Research Laboratory, the South Pole-Aitken (SPA) basin impact event at 4.3 Giga annum (Ga one billion years) excavated this FeS from the sulphur-enriched primitive lunar mantle, while the KREEP (K stands for atomic layer for potassium, REE-rare earth minerals and P-phosphorus) layer was still in the process of formation.
The subsequent impacts on the SPA basin mixed sulphur-rich materials with the nearby material at the landing site.
In conclusion, scientists at the Physical Research Laboratory say the Chandrayaan-3 landing site holds great promise place for future lunar missions to collect samples to study the evolution of the Moon.
Required fields are marked *