CNN
When NASA’s Artemis II mission embarks on a 10-day journey around the Moon, the crew will have the opportunity to view lunar surface features unseen by any other human eye.
As the astronauts fly over the mysterious far side of the Moon – the hemisphere that always faces away from Earth – they will observe a portion of the lunar landscape that Apollo astronauts couldn’t see due to the orbits of their capsules.
The upcoming historic mission, currently slated for launch no earlier than April 1, 2026, will mark the first time in over 50 years humans have ventured near the Moon, initiating a new wave of lunar exploration that could answer long-standing questions about Earth’s natural satellite. This mission represents a significant leap forward in space exploration technology and our understanding of the solar system.
“We’ve been observing the Moon throughout human history, and it’s even been visited by astronauts and numerous robotic missions,” said Jeff Andrews-Hanna, a professor at the Lunar and Planetary Laboratory at the University of Arizona. “However, there’s still a lot we don’t understand about the Moon at a very basic level.”
Crucial samples collected during the Apollo missions in the late 1960s and early 1970s laid the foundation for our current understanding of the Moon. The lunar rocks and soil offered new insights into the Moon’s origin and composition, and more recent analyses of previously untouched Apollo samples, as well as samples recovered by robotic missions, revealed the surprising discovery of water trapped in rocks previously believed to be completely dry.
However, the Apollo missions ventured to similar sites near the lunar equator on the near side of the Moon, where the terrain was flat and astronauts could remain within range of communication satellites. As scientists have approach to understand, these samples aren’t fully representative of the Moon’s diversity, Andrews-Hanna explained.
Exploring different lunar regions with the Artemis program could provide a more complete picture of the landscape and its composition, and uncover clues as to why the near and far sides of the Moon differ, how much water the Moon contains, and how the celestial body has evolved over time.
Studying the Moon could as well shed light on lost chapters in Earth’s early history, and assist confirm or refute the prevailing theory that the Moon formed after the impact of another celestial body colliding with our planet millions of years ago.
“I think of the Moon as Earth’s eighth continent,” said Noah Petro, chief of the Planetary Geology, Geophysics and Geochemistry Laboratory at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “When we study the Moon, we’re really studying an extension of Earth.”
And then there’s the promise of the unexpected.
“We’re going to have surprises,” said Petro, who also leads the science team for the Artemis III mission, which aims to return astronauts to the lunar surface in 2028. “That’s why we explore. If we knew what we were going to discover, we wouldn’t have to proceed.”
Every sample returned to Earth from the Apollo missions has been analyzed, updating textbooks with a wealth of new information about the Moon.
“I think it’s important to recognize how little we knew about the Moon before the Apollo program,” said Paul Hayne, an associate professor in the Department of Astrophysical and Planetary Sciences at the Laboratory for Atmospheric and Space Physics at the University of Colorado Boulder.
Before the Apollo landings, scientists debated whether the satellite originated elsewhere in the solar system before being captured by Earth’s gravitational field, or if it formed alongside Earth or even broke off from a rapidly rotating Earth as a mass, said Carolyn Crow, a project scientist for the Artemis IV mission, another planned lunar landing later this decade.
But samples from Apollo pointed to a novel theory about how Earth acquired such a large moon, Crow stated.
Within the samples was anorthosite, a type of igneous rock. Anorthosite is rarely found on Earth in isolation; it usually exists as a mineral component of other rocks. But the white rock was prevalent on the near side of the Moon, suggesting conditions existed for its formation, Crow explained.
“What’s needed is a very large magma ocean that crystallizes slowly, and all the anorthosite will float to the top of the ocean if it cools slowly enough,” Crow said.
The presence of anorthosite on the Moon suggested that the entire orb was once a magma ocean or completely molten. Isotopes – essentially chemical fingerprints for planetary bodies – found in the Apollo rock samples matched isotopes in Earth’s mantle, suggesting they formed at the same time.
Collectively, these findings helped scientists arrive at the current prevailing theory that a Mars-sized object collided with Earth, ejecting a mass of molten material from our planet that became the Moon.
“Earth wouldn’t be the planet it is today if it weren’t for the impact that formed the Moon,” said Andrews-Hanna. “Because of the existence of the Moon, Earth and our climate are much more stable, and that has really been fundamental to the development of life. There’s no doubt that without a Moon stabilizing Earth, humans wouldn’t have been able to evolve.”
The Apollo Discoveries Lead to Greater Mysteries
The Apollo missions revealed elements of the near side of the Moon that had never been observed before.
However, data from probes showed that the far side is completely different, raising questions that have puzzled scientists since the Apollo missions ended.
“The Moon is asymmetric in almost every way, and we don’t know why,” said Andrews-Hanna. “This global asymmetry has affected every aspect of the Moon’s evolution and remains one of the biggest mysteries in lunar science.”
The near side has a thin crust, low topography, and KREEP – a geochemical component rich in heat-generating radioactive elements. The material, left over from when the lunar magma ocean solidified, is a combination of potassium, rare earth elements, and phosphorus found in lunar rocks.
Apollo 14 and Apollo 15 landing sites were also clustered around Mare Imbrium, one of the largest craters in the solar system, and collected ejecta – material thrown out by the initial impact and spread across much of the near side of the Moon.
In contrast, the far side has a thick crust, higher elevations, and far fewer signs of past volcanic activity, Andrews-Hanna noted.
The Moon may appear as a dead rock from Earth’s perspective, but instruments placed by Apollo astronauts showed it is seismically active, with moonquakes occurring as the celestial body cools over time.
“One of the big questions we’re trying to answer is what’s going on inside the Moon,” said Hayne.
Scientists want to determine when other impact craters formed on the Moon, especially the South Pole-Aitken Basin. The crater, spanning nearly a quarter of the lunar surface, is the largest, with a diameter of approximately 1,553 miles (2,500 kilometers) and a depth of over 5 miles (8 kilometers).
Such a giant impact could have been responsible for giving the Moon its asymmetric nature. The South Pole-Aitken Basin is believed to be the oldest crater on the Moon, but its exact age is unknown, making it a primary target for future Artemis missions.
“Understanding its age is like finding this Rosetta Stone of the early solar system’s history,” said Petro.
A freezer will be brought to the Moon during the planned third lunar landing of the Artemis program, Artemis V, allowing for the return of frozen samples to Earth, Cohen said.
“We’re really trying to go to these deep polar craters where we think there might be ice, so we can understand the history of water on the Moon, which Apollo absolutely knew nothing about,” she said.
