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The Moon’s near side, the one we all see, has been the target of numerous robotic and human missions. However, our lunar companion’s far side, which is not visible from Earth, has never been explored. That changed on Jan. 2, 2019, when Chinese spacecraft Chang'e 4 made a soft landing on what is often referred to as the “dark side,” because it remained largely unseen until humans were able to send spacecraft around the Moon in 1959.
Since we only see one side, it would make sense to assume that our lunar companion is locked in place. However, that is not the case. The Moon does rotate around its own axis, but the Earth’s gravitational pull causes it to be tidally locked to our planet. This means that it rotates just once as it circles Earth. As a result, the same side faces our planet at all times.
Prior to the advent of space exploration, researchers had assumed the two sides would have similar topography. However, images of the far side, captured during close flybys of the natural satellite, showed very different features. While the near side is covered with maria, or ancient lava flows, the far side largely comprises craters.
Though there were numerous theories explaining the stark difference between the two sides, none could be verified without exploring the lunar surface. However, since the Moon’s bulk blocks all radio signals, making it impossible to establish communications with Earth from the far side, sending a spacecraft was not an option. To overcome this hurdle, In 2017, the Chinese National Space Administration launched a dedicated satellite to orbit the Moon and relay the signals. Once a reliable communication path was in place, the scientists began work on sending out a probe to explore the many astronomical mysteries of the far side.
Less than 12 hours after landing, Chang'e 4 sent back images of the moon’s far side and also successfully deployed the Jade Rabbit 2, or Yutu-2, rover, which will gather information as it traverses the lunar surface. The spacecraft then opened its three 5-meter-high (16-foot) radio antennas to make low-frequency radio astronomical observations, which researchers believe will provide insights into the solar system’s early days and perhaps even the origin of the first stars.
"Since the far side of the moon is shielded from electromagnetic interference from the Earth, it's an ideal place to research the space environment and solar bursts, and the probe can 'listen' to the deeper reaches of the cosmos," said Tongjie Liu, deputy director of the Lunar Exploration and Space Program Center for the China National Space Administration.
Also on board the Chang'e 4 is a “mini lunar biosphere” with potato and rockcress seeds, some silkworm eggs, as well as dirt, nutrients, and water. The insulated container, which is equipped with its own energy supply and a sunlight filter, is fitted with tiny cameras to enable researchers to observe if plants can grow, and survive, in the harsh lunar environment. The rockcress was selected due to its short and convenient growth cycle, while potatoes made the list because they could some day become a major food source for space settlers. As for the silkworms? The researchers believe they will help establish a sustainable ecosystem with the plants providing the silkworms with oxygen in exchange for carbon dioxide and nutrients from the Invertebrates’ waste.
"We want to study the respiration of the seeds and the photosynthesis on the moon," Xie Gengxin, chief designer of the experiment, told Chinese state-run news agency Xinhua.
While this spacecraft was unmanned, China next hopes to emulate NASA’s successful Apollo Program by sending crewed missions, and perhaps even establishing a permanent lunar base, by the early 2030s. While we are assuming they are targeting the near side of the Moon, don’t be surprised if Chinese astronauts make more history by visiting, and settling down, on the far side!
Resources: CNN.com, Phys.org,livescience.com.