A recent study has shed new light on the Moon's largest impact crater, offering a fascinating glimpse into our celestial neighbor's tumultuous past. When astronauts embark on NASA's Artemis missions, they'll likely uncover a treasure trove of clues near the Moon's south pole, helping scientists unravel the mysteries of the Moon's formation and evolution.
The research, published in the journal Nature, reveals a giant asteroid impact 4.3 billion years ago, creating the South Pole-Aitken (SPA) basin, the Moon's largest crater. This impact, occurring on the far side of the Moon, resulted in an oblong basin spanning over 1,200 miles north to south and 1,000 miles east to west. The study challenges conventional wisdom by suggesting that the impact originated from the north, not the south, as previously thought.
By comparing the SPA basin's shape to other giant impact basins in the solar system, the research team discovered a teardrop or avocado-like narrowing in the down-range direction. This finding implies that the Artemis missions will land on the down-range rim of the basin, providing an ideal location to study the oldest and largest impact basin on the Moon. The team's analysis also supports a southward impact, as evidenced by the topography, crust thickness, and surface composition.
The study offers insights into the Moon's interior structure and its evolution. It suggests that the early Moon was a magma ocean, with heavy minerals sinking to form the mantle and light minerals floating to create the crust. However, some elements, like potassium, rare earth elements, and phosphorus (KREEP), remained concentrated in the final liquids of the magma ocean. These elements are particularly abundant on the Moon's near side, mirroring the behavior of high fructose corn syrup in a frozen can of soda.
The KREEP-rich material and heat-producing elements became concentrated on the near side, causing intense volcanism and forming the dark volcanic plains that we see from Earth. The reason for this concentration and the material's evolution over time remains a mystery. The Moon's crust is thicker on the far side, and this asymmetry has influenced its evolution, including the latest stages of the magma ocean.
The study of the SPA impact crater revealed an unexpected asymmetry, with the western side rich in radioactive thorium and the eastern side lacking it. This suggests that the impact created a window through the Moon's skin, separating the KREEP-enriched magma ocean crust from the 'regular' crust. The distribution and composition of these materials align with the predictions from modeling the magma ocean's evolution.
Despite the progress, many mysteries surrounding the Moon's earliest history persist. Remote sensing data and samples brought back by astronauts will provide crucial insights into the Moon's composition and evolution. The University of Arizona's state-of-the-art facilities will play a significant role in analyzing these samples, offering a deeper understanding of the Moon's early evolution.
