A new study, published in Science Advances, has refined some important details about the moon’s largest and oldest impact crater, which stretches more than 1,200 miles (2,000 km) on the far side of the moon. The new details can help guide some of the planning for NASA’s upcoming Artemis mission to the moon, which is planned for 2028.

The South Pole–Aitken (SPA) basin is the moon’s largest and oldest confirmed impact basin. The basin has a unique, tapered elliptical shape that has puzzled scientists and sparked some debate over the direction and nature of the impact that formed it. Some asymmetries in the crust suggest a northward trajectory of the impactor, while the shape and the structure of the basin suggest a southward trajectory.

The authors of the new study write, “Large basins on the moon and other solid bodies (e.g., Mars and Pluto) are ellipses that taper in the downrange direction. SPA’s tapering toward the south, a steeper crustal thickness gradient toward the north, and the presence of a thorium-and iron-rich deposit toward the southwest of SPA beyond the basin rim support a southward impact trajectory.”