'Tremendous implications': Moon's biggest crater reveals lunar formation secrets

The biggest crater of the moon, which covers nearly a quarter of its surface, has revealed new information regarding its formation and scientists believe it has ''tremendous implications''.

The study published in JGR planets shows an analysis of the South Pole-Aitken Basin (SPA), that is 2500km in diametres and approximately 8.2 km deep, that has refined the timeline of the development of lunar mantle and crust.

According to Daniel Moriarty, planetary geologist of NASA's Goddard Space Flight Center and the lead researcher of the study, ''These results have important implications for understanding the formation and evolution of the Moon.''

Like the Earth, the Moon is layered into a crust and mantle. The Moon's layering was shaped by an early global melting event known as the “Lunar Magma Ocean.”

As the magma ocean solidified, dense minerals sank to form the mantle, while less dense minerals floated to form the crust.

Elements such as thorium are not easily incorporated into mineral structures and remain in the liquid. Because of this, a thorium-rich dreg layer was sandwiched between the crust and mantle. These dregs are very dense and are expected to sink into the underlying mantle during or soon after crystallization.

The Moon's largest and oldest impact basin excavated material from this dense, thorium-rich layer before it sank.

The exposed material was then diluted and obscured by four billion years of impact cratering and volcanic eruptions. However, we identify several pristine exposures created by recent craters.

The impact basin also melted rocks from greater depths than the rocks it ejected. These melted rocks exhibit a much different composition.

This indicates that the lunar upper mantle included two compositionally distinct layers that were exposed in different ways by this large impact event. These results have important implications for understanding the formation and evolution of the Moon.

The researchers wrote in their paper ''Formation of the South Pole-Aitken Basin is among the most ancient and important events in lunar history. Not only did it affect the thermal and chemical evolution of the lunar mantle, but it preserved heterogeneous mantle materials on the lunar surface in the form of ejecta and impact melt.''

''As we enter into a new age of international and commercial lunar exploration, these mantle materials at the lunar surface must be considered amongst the highest-priority targets for the advancement of planetary science," they added.