Marius Hills

[5] The hole, first discovered by the Japanese SELenological and ENgineering Explorer (SELENE) and then later imaged by the Lunar Reconnaissance Orbiter[7] has been the subject of much research and speculation.

[9] Additional radar echo patterns suggesting intact lava tubes have been found at several other locations around the Marius Hills, which correspond to areas of mass deficit in the GRAIL data.

[10] The Marius Hills region was at one time considered a possible landing site for a lunar landing mission during the American Apollo program (eventually becoming the alternative site for Apollo 15), with the possibility of gaining insight about the volcanic history of the Moon from domes in the area.

[11] A site in the northern Marius Hills, located in the center of a five-kilometer circle in a shallow valley between four domes near a small sinuous depression, was one of nine potential Apollo landing sites studied in-depth as part of a 1968 Bellcom report describing the geology of those nine locations and potential mission plans.

This site in particular, the Bellcom study suggested, could have offered the opportunity for up-close examination of planetary ridges similar to those located at the bottoms of Earth's oceans and sampling of a variety of material from the Moon's interior churned up during the area's highly active volcanic past.