India’s landmark moon mission, the Chandrayaan-3, which achieved a historic milestone with the successful soft landing of the Vikram lander in the high-latitude highland region near the south pole of the Moon, has provided invaluable data leading to a ‘groundbreaking’ discovery. The data from the Pragyan Rover depicted the landing site to be near a semi-circular, heavily degraded structure. It was believed to be a buried impact crater, approximately 160 km in diameter. The site is believed to predate the South Pole-Aitken (SPA) basin. The SPA basin is estimated to have formed around 4.2 to 4.3 billion years ago

This site, located approximately 350 km northeast of the South Pole-Aitken (SPA) basin rim, is an ancient and highly cratered terrain that offers a unique opportunity to study the Moon’s geological history. This ancient regolith, the layer of dust and rock on the Moon’s surface, is essential for understanding lunar formation and evolution. The Rover captured high-resolution images through its cutting-edge optical cameras providing insight into the structure of the crater.

The study on Science Direct by scientists at Ahmedabad’s Physical Research Laboratory, revealed that the landing site is located in an area that has undergone a complex sequence of ejecta emplacement from the SPA basin and other nearby impact basins and craters. The SPA basin, a major contributor of ejecta, deposited nearly 1400 meters of ejecta materials, while 11 other basins contributed around 580 meters.

The goal of this study is to understand the role and influence of basin-forming impacts and complex craters around the Chandrayaan-3 landing site. The study also evaluates the results of small-size crater density derived from the Navigation Camera on the Pragyan rover (Navcam) along its covered path, comparing these findings with data from the Orbiter High-Resolution Camera (OHRC) on board the Chandrayaan-2 orbiter.

The Chandrayaan-3 mission has led to the identification of several new small craters by the Pragyan rover Navcam. The comparison of in-situ rover images with high-resolution orbiter images revealed that a significant number of smaller craters are only visible from in-situ imaging, indicating a higher crater density and flux than previously estimated from orbiter data. This mission not only enhances understanding of the Moon’s geological history but also paves the way for future lunar exploration and scientific discoveries.

What is Ejecta emplacement?

Ejecta emplacement refers to the process by which material is ejected from an impact crater and deposited over the surrounding terrain. This material, known as ejecta, is typically composed of rock, dust, and other debris that is blasted out during the formation of an impact crater. The distribution of ejecta depends on the size and velocity of the body that causes the impact, as well as its angle of impact.

Ejecta can also create secondary craters when larger fragments impact the surface again. These secondary craters are typically smaller and less deep than the primary crater.

Studying ejecta emplacement helps scientists understand the history of impacts on a planetary body. The composition and distribution of ejecta can provide insights into the materials and the processes that have shaped the surface over time.

Additionally, other complex craters added up to 90 meters of ejecta, and secondary craters located adjacent to the landing site contributed approximately 0.5 meters of ejecta. These materials are crucial for the Pragyan rover’s in-situ analysis.

Implications of the findings

The Chandrayaan-3 mission provides a rare opportunity for scientists to study deeply buried materials dating back to the Moon’s formation, offering new insights into lunar evolution. The region hosts some of the most deeply excavated materials on the Moon, making it a valuable site for geological study.

Impact crater density, distribution, and degradation serve as indicators of relative changes over the lunar surface. The density of superposed craters provides direct evidence for resurfacing or altering craters. Crater degradation is more extensive near larger complex craters or impact basins due to ballistic sedimentation and secondary cratering. The ejecta emplacement from these craters mantles pre-existing craters, significantly affecting older craters. This process of erasing older craters with new impacts leads to a steady state in the population of visible craters.

Exploring ancient lunar terrains with high crater density, such as the lunar south pole region, presents significant challenges. The ejecta distribution around the Chandrayaan-3 landing site is crucial for understanding the origin of materials, the depth of excavated materials, and the nature of modifications over geological timescales.