The Chinese Chang'e 4 mission was supposed to continue for 12 months; the Yutu-2 rover was supposed to be operational for no more than 3 months... Both spacecraft that were sent to the Moon have now lasted over 1000 days on the far side of the Moon.
The day China landed on the far side of the Moon
The Chang’e-4 mission was launched by China in December 2018, and a month later, the landing platform made the first-ever soft landing on the far side of the moon. The mission includes two vehicles – a landing platform and a lunar rover “Yutu-2” fixed on it, which on January 4, 2019, landed on the surface and began an independent exploration of the Moon.
Since the spacecraft on the far side of the Moon cannot communicate directly with the Earth, the active phase of preparation for the mission began in mid-2018, when China launched the Queqiao relay satellite. It is in a halo orbit around the Lagrange point L2 of the Earth-Moon system, due to which it constantly sees both the landing platform with the lunar rover and the Earth.
A few days after the landing, the China National Space Administration released a series of images and videos including the actual landing of the platform.
Deployment of the lunar rover
Another day later, the agency published video footage of the Yutu-2 lunar rover landing on the far side of the Moon and its movement along it. They were taken with a camera mounted on the Chang’e-4 landing platform.
Around mid-day January 4, 2019, the Yuytu-2 lunar rover left the station and drove away from it, the resulting track in the ground was photographed by the cameras of the landing platform.
The six-wheeled rover itself weighs 140 kilograms and is equipped with a panoramic camera, radar, a spectrometer for studying the composition of the soil and exosphere of the Moon, and an analyzer of neutral atoms to study the interaction of the solar wind with the surface of the Moon.
The mission had several main tasks – photographing the surface of Earth’s satellite, studying the composition of the soil, and testing the possibility of conducting radio astronomy observations – it is assumed that in the future it will be possible to install a radio telescope on the lunar surface for observations without interference from the Earth.
In addition, a sealed container with silkworm eggs and plant seeds was installed inside the landing platform for a biological experiment to create a closed ecosystem. Here are several of the main discoveries that Chang’e 4 and Yutu-2
Creating a closed biosphere on the Moon
A cotton seed sprouted inside an airtight container of culture medium as part of a Lunar Micro Ecosystem biological experiment. In addition to cotton seeds, the container contains seeds of potatoes, rapeseed, and Arabidopsis thaliana, fruit fly eggs, and yeast; light can penetrate into it.
The experiment itself began on January 3, shortly after the landing of the station, when the seeds were watered and received a source of illumination. As a result, it was possible to germinate a cotton seed, which became the first plant on the moon.
The images of the sprout were obtained using a micro-camera that constantly monitors the processes going on in the container, which is installed inside the landing platform. The purpose of the experiment was to create a closed mini-biosphere under conditions of lunar gravity, increased radiation load, and temperature drops.
Measuring the level of radiation on the far side of the Moon
One of the main risk factors in space is background radiation, which mainly consists of many charged particles emitted by the Sun or other galactic sources. When particles fly through biological tissues, their energy can be enough to damage molecules in their path. The Earth’s surface is shielded from radiation by the atmosphere, in which the particles are decelerated and the background weakens, but in open space or on the surface of other celestial bodies (for example, the Moon) such protection is absent.
The Lunar Lander Neutrons and Dosimetry experiment (LND) of the Chinese Chang’e-4 mission measured the level of radiation on the lunar surface as a function of time for the first time. The equivalent radiation dose rate was about 1369 microsievert per day, which is approximately 1.9 times higher than the same figure onboard the International Space Station and approximately 200 times higher on the Earth’s surface.
Yutu-2 found minerals from the mantle at the bottom of a lunar crater
The size of the moon is large enough, which allowed its constituent matter in the early stages of formation, when it was a liquid ocean of molten rocks, to split into a denser core, light crust, and mantle of intermediate properties.
At the same time, the Moon is small enough and therefore quickly cooled down and solidified in its original form, which excluded the possibility of the appearance of active tectonics, as on Earth. Due to this, its insides are of exceptional interest for science, since their study can help clarify the evolution of the insides of bodies of planetary sizes.
However, 60 years of research on the Moon has only allowed a detailed study of its crust, while the mantle, which should contain more heavy elements such as iron and manganese, remains inaccessible for direct research. At the moment, scientists do not know the composition of the rocks that form it.
Potentially, the fall of meteorites, which gave rise to the largest craters, can break through the crust and lead to the appearance of mantle material on the surface of the Moon. The largest and oldest impact crater on the Moon is the South Pole-Aitken basin, located on the opposite side, which is more than 2 thousand kilometers in size and is about 8 kilometers deep. Research with the help of orbiters indicated the possible presence of rocks from great depths, but remote measurements are not enough for unambiguous conclusions.
Weeks after Chang’e-4 landed in the Von Karman crater, researchers presented the primary results of the processing of data from a visible and near-infrared spectrometer. The samples studied differ significantly from the usual material of the lunar surface. In particular, the scientists came to the conclusion that they came across mainly olivine and pyroxene with low calcium content.
The researchers suggested that these rocks were originally part of the upper mantle of the Moon, but were thrown to the surface by a shock event, which resulted in the South Pole – Aitken basin. This material could then be redistributed once again during the formation of the 72-kilometer Finsen crater, which borders Von Karman.
However, due to the complex nature and partial intersection of the spectral features of the minerals, as well as the presence of various compounds in each sample, based on the data obtained, it is very difficult to draw full-fledged conclusions about the relative abundance of various minerals in the mantle.
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• Bartels, M. (2019, September 26). Here is China’s most detailed view yet of its Chang’E-4 landing site on the far side of the Moon. Space.com.
• Chang, K. (2020, February 26). China’s Rover finds layers of surprise under Moon’s far side. The New York Times.
• Greshko, M. (2021, May 3). China just landed on the far side of the moon: What comes next? Science.
• Jones, A. (2021, October 5). 1,000 days on the moon! China’s chang’e 4 lunar far side mission hits big milestone. Space.com.