The astronauts of NASA’s Artemis II mission are expected to pass by the dark side of the moon until the early hours of Tuesday (07/04), as all attention now turns to the mission control center at Johnson Space Center. Lunar scientists are showing particular interest, as the unseen side of the moon differs significantly from the side that faces Earth: it has a thicker crust, many more impact craters, and very few of the extensive frozen lava plains that characterize the visible side. Based on the current trajectory of the Orion capsule, Artemis II scientists in Houston are continuously updating their predictions for what the crew will be able to observe.
Artemis II: Excited astronauts will see geological features on the illuminated portion of the moon’s far side
The lighting conditions, unfortunately, are not ideal. The moon and sun are positioned in such a geometry that only 20% of the dark side will be illuminated when the astronauts pass by. This is somewhat disappointing for scientists, who had hoped a broader area would be visible. However, they remain excited that the astronauts will see geological features on the illuminated portion of the moon’s far side and gave Nature a first taste of what to expect.
What’s at the top of many researchers’ lists
At the top of many researchers’ lists is the Orientale Basin, a giant impact basin with a diameter of 930 kilometers in the moon’s southern hemisphere. This is the largest and youngest of the basins formed during the period of the so-called Late Heavy Bombardment, a prolonged asteroid storm that began about 4 billion years ago. Its three concentric rings are estimated to have been created when a massive asteroid struck the moon, vaporizing material that was ejected outward like a tidal wave and caused the collapse of the moon’s crust around the impact point.
The significance of Orientale
Orientale “is hugely important for understanding impact crater formation throughout the solar system,” says Kelsey Young, Artemis II’s lead lunar scientist. Because it is so large and detailed, scientists use it as a template to understand how impact basins form on other planets. Although it has already been imaged by robotic spacecraft, its full view has essentially never been observed by human eyes.
During the flyby, other craters that have not been visually observed under sunlight will also be illuminated, such as Ohm crater, 64 kilometers in diameter, with a central peak rising above lava flows on its floor, and Pierazzo crater, 9 kilometers in diameter. The astronauts will try to detect subtle changes in surface color and brightness, and observe how the changing angle of sunlight alters the perception of lunar topography. According to mission scientists, this direct human observation could add new elements to the detailed photographs already collected by orbital spacecraft.
Cameras at the ready
The Artemis II crew will also see Earth setting and rising over the lunar horizon, recreating the historic “Earthrise” image first captured by Apollo 8 astronauts in 1968. For nearly an hour, as Orion passes the far side, the astronauts will be able to watch a solar eclipse when the moon blocks the sun. They will then observe and photograph the solar corona while searching for any bright flashes on the moon’s surface from meteorite impacts.
All these images will be recorded with three Nikon cameras, one of which has a telephoto zoom up to 400mm. The astronauts also have iPhones with them for more informal shots. At the closest approach point, Orion will be about 6,600 kilometers above the lunar surface, with the moon appearing about the size of a basketball held at arm’s length.
