Artemis II: Geology from Orbit

The Apollo 8 astronauts provided the first and most detailed human observations of the far side of the Moon, all while testing systems and procedures that became critical to the success of future Apollo missions. During their time in orbit, the Apollo 8 astronauts observed and documented key geologic features, such as Tsiolkovsky crater, the Sea of Tranquility, and the Taurus-Littrow Mountains. Those observations ultimately helped mission engineers plan for future Apollo missions, and helped scientists better understand the stark geologic differences between the near and far side of the Moon. Several of the maps that the Apollo 8 astronauts used to make and document their observations are on display in the Destination Moon exhibition at the Museum in Washington, DC.

Fifty-eight years after the Apollo 8 astronauts first set eyes on the far side of the Moon, NASA astronauts have another opportunity to observe the geology of the lunar far side during the Artemis II mission. The Artemis II mission will see astronauts Reid Weisman, Victor Glover, Christina Koch, and Jeremy Hansen slingshot around the far side of the Moon at an altitude of 4,000-6,000 miles above the lunar surface onboard the Orion capsule aptly named Integrity. At that distance, the astronauts onboard will have travelled farther from Earth than any human being before them, and they will be able to observe many of the same geologic features that were observed for the first time by the crew of Apollo 8. Given the unique orientation of the Sun relative to the Earth and Moon during the Artemis II mission, some areas of the lunar surface that were in shadow during the Apollo missions may even be observed by human eyes for the first time during Artemis II.

The far side of the Moon is geologically distinct from the near side in several key ways. Most obvious is the absence of voluminous, ancient lava flows on the lunar far side. These lava flows, collectively termed the “lunar maria,” are widespread on the near side of the Moon and are visible from Earth via just the naked eye on a clear night. They formed progressively between 1.2 to 3.8 billion years ago, but the exact reason for their absence on the lunar far side is not fully understood.

The majority of the terrains that make up the lunar far side are known as the “lunar highlands.” The lunar highlands are composed of more ancient geologic materials that primarily contain the rock Anorthosite. The low density, lightly colored minerals that make up Anorthosite give the lunar highlands their bright appearance that contrasts with the dark, volcanic lunar maria. These types of color differences will be one tool that the Artemis II crew will use to decipher various geologic features on the lunar surface.

During their dedicated observation window, the Artemis II crew will rely on their Nikon  cameras and extensive geology training to identify and observe various geologic targets across the lunar far side including ancient impact craters, volcanic deposits, and tectonic faults. Some of these features, such as the Orientale Basin, will appear large and quite obvious to the astronauts. At roughly 580 miles (930 km) wide and 3.8 billion years old, the Orientale Basin is the youngest major impact basin on the Moon. The rocks surrounding the basin likely contain material from deep within the Moon's interior that was excavated during basin formation—making the region a target for past and future scientific investigations.

The Artemis II crew will also have the opportunity to observe more subtle geologic features, such as lobate scarps, which are the surface expression of tectonic faults that formed more recently due to the interior cooling and global contraction of the Moon. Similar to how faults on Earth are common sources of earthquakes, the lobate scarps are also potential sources of moonquakes and offer scientific opportunities for upcoming lunar science missions that seek to improve the understanding of lunar seismicity and the lunar interior structure.

It's not just the sunlit areas of the lunar far side that will provide opportunities for geologic observations. The Artemis II crew will also observe the dark, shadowed regions of the lunar surface for impact flashes. Impact flashes occur when a small asteroid strikes a shadowed portion of the lunar surface and produces a bright flash of light that contrasts starkly against the dark, shadowed lunar surface. During the Apollo 17 mission in 1972, astronaut Harrison Schmitt observed this phenomenon on three separate occasions while in orbit around the Moon. If the Artemis II astronauts were to observe similar impact flashes, it would help scientists better understand the rate at which asteroids collide with planets and moons in our solar system today.

While the Artemis II mission will stop short of putting boots on the ground, it is an incredibly important precursor mission that will pave the way for future missions to the surface of the Moon and Mars. The geologic observations made during Artemis II will help scientists to plan for the upcoming Artemis IV mission to the lunar south pole and answer key questions about the origin of the Moon; thus, marking another milestone in lunar science and space exploration.