Beijing, China · 3 January 2019
China's Chang'e-4 lunar mission made history at 02:26 UTC on 3 January 2019, when its lander touched down in the Von Kármán crater on the far side of the Moon. No spacecraft had ever achieved a soft landing on the lunar far side before. The lander immediately began surface operations, and within hours deployed its companion rover, Yutu-2, to begin exploring the terrain of the South Pole-Aitken Basin — one of the largest and oldest impact craters in the solar system.
The China National Space Administration (CNSA) confirmed the landing via the Queqiao relay satellite, which had been launched in May 2018 and positioned in a halo orbit around the Earth-Moon Lagrange point 2 (L2) to serve as a communications bridge between the far-side lander and ground stations on Earth.
Why the Far Side Matters
The Moon is tidally locked to Earth, meaning the same hemisphere always faces our planet. The far side — often mistakenly called the "dark side" — is never directly visible from Earth, making direct radio communication with any spacecraft there impossible without a relay. Previous missions had orbited or impacted the far side, but none had landed.
The far side is scientifically valuable for several reasons:
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Geological diversity: The far side has a thicker crust and a markedly different composition from the near side, with far fewer mare (dark volcanic plains). The South Pole-Aitken Basin, where Chang'e-4 landed, is a roughly 2,500-kilometre-diameter impact structure — one of the largest known impact craters in the solar system — that excavated material from deep within the lunar crust and possibly the upper mantle.
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Radio-quiet environment: The far side is shielded from Earth's intense radio-frequency interference, making it an ideal location for low-frequency radio astronomy observations of the early universe — a key science goal of the mission.
The Queqiao Relay Satellite
Solving the communications challenge required the Queqiao ("Magpie Bridge") relay satellite, launched on 21 May 2018 aboard a Long March 4C rocket from the Xichang Satellite Launch Center. Queqiao was placed into a halo orbit around the Earth-Moon L2 Lagrange point, approximately 65,000 kilometres beyond the Moon, where the gravitational forces of Earth and the Moon allow a spacecraft to maintain a relatively stable position. From this vantage point, Queqiao can simultaneously maintain line-of-sight contact with both the far-side lander and ground stations on Earth.
Two micro-satellites, Longjiang-1 and Longjiang-2, were also launched alongside Queqiao. Longjiang-2 successfully entered lunar orbit and conducted amateur radio experiments, while Longjiang-1 was lost during the transit phase.
Scientific Instruments and Objectives
Chang'e-4 carried a suite of instruments developed by Chinese institutions and international partners:
| Instrument | Function | Provider |
|---|---|---|
| Lunar Penetrating Radar | Subsurface imaging and stratigraphy | China |
| Visible and Near-Infrared Imaging Spectrometer | Mineral composition analysis | China |
| Lunar Neutron and Radiation Dose Detector | Radiation environment measurement | Germany (Kiel University) |
| Neutral Atom Detector | Solar wind interaction studies | Sweden (IRF) |
| Low-Frequency Spectrometer | Radio astronomy observations | China |
| Lunar Lander Neutrons and Dosimetry | Radiation dosimetry | Germany (DLR) |
The Yutu-2 rover was equipped with a panoramic camera, a lunar penetrating radar for subsurface profiling, and a visible/near-infrared imaging spectrometer for mineralogical analysis. The rover's primary task was to traverse the crater floor, characterise the local geology, and investigate the composition of materials excavated by the ancient South Pole-Aitken impact.
Early Discoveries
In May 2019, the Yutu-2 rover's lunar penetrating radar revealed a layered subsurface structure in the Von Kármán crater, identifying a highly weathered regolith layer approximately 12 metres thick overlying coarser ejecta deposits. The visible/near-infrared spectrometer detected materials rich in olivine and low-calcium pyroxene, consistent with origins from the lunar upper mantle — offering the first in-situ evidence of mantle-derived material on the lunar surface.
A Biosphere Experiment
Chang'e-4 also carried a biological experiment — a small, sealed canister containing cotton, potato, and rapeseed seeds, along with yeast and fruit fly eggs. The cotton seeds successfully germinated, marking the first time any biological growth had been achieved on the lunar surface. However, the experiment was short-lived: the canister's internal temperature dropped to approximately −52°C during the lunar night, ending the experiment after one lunar day. While scientifically modest, the demonstration carried implications for future long-duration human missions that would require sustainable food production.
International Context
Chang'e-4 was the fourth mission in China's lunar exploration programme, named after the Chinese moon goddess Chang'e. The programme began with the Chang'e-1 and Chang'e-2 orbiters (2007 and 2010), followed by the Chang'e-3 lander and Yutu rover, which soft-landed on the near side in December 2013. Chang'e-4 was originally built as a backup to Chang'e-3 and was repurposed for the far-side mission.
The mission also carried a Dutch-built radio antenna (NCAM) developed by the Netherlands Institute for Radio Astronomy (ASTRON), designed to detect low-frequency radio signals from the early universe — observations impossible from Earth or Earth orbit due to ionospheric interference.
Yutu-2's Longevity
The Yutu-2 rover was designed for a nominal mission lifetime of three months. In practice, it far exceeded expectations, continuing to operate for more than five years. By early 2024, the rover had travelled over 1,500 metres across the lunar surface, making it the longest-lived lunar rover in history. Each lunar day (approximately 29.5 Earth days), the rover would wake, conduct observations, and then hibernate during the two-week lunar night to conserve power and protect its electronics from the extreme cold.
Sources
- China National Space Administration (CNSA), Chang'e-4 mission announcements, January 2019
- Xinhua News Agency, "China's Chang'e-4 probe lands on Moon's far side," 3 January 2019
- Li, C. et al., "Chang'E-4 initial spectroscopic identification of lunar far-side mantle-derived materials," Nature 569, 378–382 (2019)
- Lai, J. et al., "Comparison of dielectric properties and structure of lunar regolith at Chang'e-4 and Chang'e-3 landing sites," Planetary and Space Science (2019)
- NASA Goddard Space Flight Center, LRO images of Chang'e-4 landing site, 2019
- Wikipedia, "Chang'e 4" —
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