Far side of the Moon

The far side of the moon is the side of the moon’s surface that is always turned away from Earth. The far side’s mysterious, inaccessible nature has intrigued humanity for generations. Human exploration of space has discovered that the two sides of the moon have very different traits. Astronomers have been interested in learning more about these differences, believing that it could help them better understand the moon’s development, which in turn could provide clues to how other objects in the solar system formed. The far side of the moon has often been referred to as the dark side of the moon. This is only accurate when “dark” is used as a description of something mysterious or unknown. While it never faces Earth, the far side receives sunlight just as frequently as the “near” side that constantly faces Earth.

History

In the mid-twentieth century, the United States and the Soviet Union were the predominant powers on Earth. Both nations competed against each other to achieve military, political, and scientific dominance. Because both nations possessed nuclear weapons and feared that direct conflict would result in a catastrophic war, they did not engage in military combat with each other. Instead, they conducted a forty-year-long ideological battle of influence known as the Cold War.

One important facet of the Cold War was the Space Race. Both nations began developing technology that allowed them to send satellites—and eventually humans—into space. Space travel was seen as the next major hurdle for humanity to overcome, and there was extreme pressure on both sides to be the first to make major breakthroughs in the field.

Both sides made tremendous strides throughout the 1950s and 1960s, which led to humanity’s first looks at the far side of the moon. In 1959, the Soviet satellite Luna 3 captured the first images of the far side. Six years later, the Soviet satellite Zond 3 returned with higher-quality images. In 1968, NASA launched the Apollo 8 mission, the first manned mission to successfully orbit the moon and return to Earth. Astronauts Frank Borman, Jim Lovell, and William Anders became the first humans to see the moon’s far side. They also witnessed an “Earthrise,” a view from their perspective in which the planet Earth emerged from behind the moon’s horizon. The image became one of the most iconic pictures associated with space travel.

Astronauts from the United States first landed on the moon in July 1969. Several more manned missions followed before NASA ended the program in 1972. The Apollo spacecraft that landed on the moon’s surface always landed on the near side; reaching the far side held significant challenges. The moon itself blocks radio signals and other forms of communication that an Earth-based mission control would require. Lacking that communication would make manned flights far more difficult. Landing, taking off again, and returning to Earth without the benefit of communication is not a task that space programs were prepared to undertake. Alternative plans involving unmanned, expendable vessels were an option, but finding a way to communicate with Earth remained a problem.

Overview

Only one side of the moon faces Earth due to a phenomenon called tidal lock. Over time, the gravitational pulls of Earth and the moon have forced the moon into an unusual orbit. The moon makes one full rotation in the same amount of time that it takes to complete one full orbit of Earth. Several other moons of other planets in the solar system are tidally locked as well; the planet Mercury is tidally locked to the sun.

Because the moon’s orbit is elliptical rather than perfectly round, about 59 percent of its surface is visible in total, with some portions visible at different times than others. This leaves a significant portion of the moon that cannot be observed from Earth. This side is also unable to receive radio signals from Earth.

Satellites capable of orbiting the moon became more common over the course of the twentieth century, and their imaging technology grew more sophisticated. By observing the images and tracking the orbits of these satellites, scientists realized that the moon’s crust seemed to be significantly thicker on its far side. The surface is also very different. The near side is dominated by dark plains called maria. The name was derived from the Latin word for sea because early observers believed that the moon contained vast oceans. These plains are primarily made of basalt, and scientists theorize that ancient volcanoes were responsible for the creation of maria in the distant past.

The far side has more rugged terrain with only a small amount of maria. Craters on the far side tend to be smaller but more numerous than those on the near side. One exception is the South Pole-Aitken basin, one of the largest known impact sites in the entire solar system. It is approximately 1,367-miles (2200-kilometers) wide, and is home to the 115-mile (185-kilometer) Von Karman crater.

In December 2019, China’s space program launched the Chang’e-4, a craft designed to land on the far side of the moon. The following month, it became the first craft to execute a successful soft landing on the moon’s far side, touching down in Von Karman crater. In a soft landing, the spacecraft is undamaged. The craft was equipped with a rover—Yutu-2—that could explore the moon’s surface and collect data and samples. The vehicles communicated with Earth via a relay satellite that had been launched into the moon’s orbit earlier in 2018. By 2022, Yutu-2 had traveled more than 3,300 feet (1,100 meters). As of 2024, Yutu-2 was still active. Astronomers hoped that the mission’s findings would greatly increase humanity’s understanding of the moon and possibly reveal more about the nature of celestial bodies in general.

One aspect of scientific interest on the far side is the nature and composition of the rock. Comparing it to samples taken on the near side could help scientists understand why the two sides are so different. Astronomers also hope to learn more about the moon’s deepest craters. Light may have never reached some of them, and some scientists have theorized that water ice may be present there. The lack of radio signals from Earth has also made the far side a possible candidate for an observatory or radio-based experiments. One such experiment began in 2024. NASA has a program called commercial lunar payload service (CLPS). It uses uncrewed landers to conduct science experiments on the moon. The first landings collected information about the environment near the moon's south pole. By 2026, NASA planned to land radio telescopes on the far side of the moon. NASA believed the far side of the moon was an ideal place to conduct radio astronomy because it is not exposed to Earth's ionosphere, or magnetic field, which distorts and scrambles radio signals. NASA hoped to learn more about plasma, which is solar wind that directly strikes the moon's surface. By doing this, NASA could help keep astronauts on the moon safe.

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