The successful exploration of the Moon’s far side represents a monumental achievement in space exploration, offering humanity an unprecedented view of a previously hidden lunar hemisphere. China’s Chang’e 4 mission, launched in late 2018, marked the first time any spacecraft had completed a soft landing on this mysterious region. This historic endeavor opened a new chapter in planetary science, demonstrating the technical capability to study an environment shielded from Earth. The mission’s findings have provided unique data, ranging from the Moon’s deep geological history to the possibilities for future space biology experiments.
The Historic Landing on the Far Side
Landing a spacecraft on the Moon’s far side is technically challenging because the Moon is tidally locked with Earth, meaning the same side always faces our planet. This configuration prevents any direct line-of-sight communication between a lander and ground control stations on Earth. To solve this communications barrier, the mission first launched the Queqiao relay satellite into a halo orbit around the Earth-Moon L2 Lagrange point. This strategic orbital position, located beyond the Moon, allows the satellite to maintain simultaneous visibility with both the Earth and the Chang’e 4 lander. The probe and its Yutu-2 rover ultimately touched down inside the Von Kármán crater, a large, ancient impact feature located within the vast South Pole-Aitken Basin.
Uncovering Lunar Subsurface Composition
The primary scientific goal of the Yutu-2 rover was to investigate the geology of its landing site, which is part of the largest and deepest known impact structure on the Moon. Scientists theorize that the massive impact that created the South Pole-Aitken Basin was powerful enough to excavate material from the Moon’s deep crust or even its upper mantle. Analyzing this material offers direct insights into the Moon’s internal composition and formation history.
Using its Visible and Near Infrared Spectrometer (VNIS), the rover identified two key minerals in the lunar soil consistent with this theory: olivine and low-calcium pyroxene. These minerals are thought to be major components of the lunar mantle, the layer beneath the crust. This finding provides the strongest evidence yet for the existence of mantle-derived material on the lunar surface, validating models of the Moon’s interior structure.
The Yutu-2 rover also employed its Lunar Penetrating Radar (LPR) to map subsurface structures. LPR data revealed a complex stratigraphy beneath the landing site, showing multiple distinct layers of ancient lava flows. These layers, some extending to depths of over 300 meters, represent successive episodes of volcanic activity that filled the crater over billions of years. Mapping the thickness and composition of these deep layers provides a detailed geological history of the far side.
The First Biological Growth on the Moon
Beyond the geological studies, the Chang’e 4 lander carried a unique experiment called the Lunar Mini-Biosphere to test the possibility of supporting life in the lunar environment. This sealed, cylindrical canister contained seeds from multiple plant species, including cotton, rapeseed, and potato, along with fruit fly eggs and yeast. The goal was to create a simple, self-sustaining micro-ecosystem under lunar conditions. The experiment was a success, as a cotton seed was the first organism to germinate and sprout a small leaf on the Moon. This brief success demonstrated that plant life could begin its growth cycle under the low gravity and harsh radiation environment. However, the plant’s life was short-lived, as the experiment was unable to survive the extreme temperature drop of the two-week-long lunar night.
Unique Opportunities for Radio Astronomy
The far side of the Moon offers an unparalleled environment for low-frequency radio astronomy. This hemisphere is naturally shielded from the constant barrage of radio interference emanating from human activity on Earth, creating the most radio-quiet location in the inner solar system. The Chang’e 4 lander included a Low-Frequency Spectrometer (LFS) to take advantage of this unique location. The instrument’s observations focused on the low-frequency end of the radio spectrum, which is otherwise obscured by Earth-based noise. This capability holds particular significance for studying the Cosmic Dark Ages, a period before the first stars and galaxies formed. By detecting the subtle 21-centimeter wavelength signal from neutral hydrogen gas during this era, scientists hope to gain a deeper understanding of how the universe emerged from darkness.