Chang'e-4: China's Rover Encounters "Snow"-Like Surface on Moon's Far Side

Approximately 238,855 miles from Earth, a Chinese space rover watches the world float from the far side of the moon. On Friday, Jade Rabbit 2 drove off the Chang’e-4 lander’s ramp and became the first mobile probe to explore the side of the moon facing away from Earth. Images released by the China National Space Administration show the six-wheeled rover moving its way over the lunar surface, leaving two narrow trails behind it.

The track marks left by Jade Rabbit 2, also known as Yutu-2, rover designer Shen Zhenrong of the China Aerospace Science and Technology Corporation told CCTV, are embedded in the region’s soft surface, a terrain that he says is “similar to that when you are walking on the snow.”

While the landscape of the moon may evoke images of rock chunks and craters, the moon’s upper surface is actually covered by a layer called the regolith. The bulk of this layer is a fine, extremely light gray soil, and the thickness of the regolith and soil layer can range from a few meters to tens of meters, depending on the age of the terrain.

Juliane Gross, Ph.D., an associate professor of planetary sciences at Rutgers University and a NASA early career fellow, explains that the existence of this fine soil is because of eons of space weathering.

Jade Rabbit 2 rolls over the snow-like surface.China National Space Administration

“For billions of years, the lunar surface has been impacted and bombarded by charged atomic particles [solar wind] and by materials at all spatial scales, from smaller than a grain of sand events to big impact basin-forming events,” Gross tells Inverse. “This process is largely one of mechanical space weathering and had the effect that the upper surface layer of the Moon got fractured, broke-up, excavated, brecciated, melted, and redistributed.”

It doesn’t surprise her that Jade Rabbit 2 is cruising over a smooth surface. Over time, Gross explains, the upper surface rocks and particles of the regolith layer are ground to finer and finer sizes. This layer of material is the lunar soil, which she says “is similar to dust — or snow I guess — and thus makes the lunar surface appear ‘soft.’”

Von Kármán is the mission's landing site.Wikimedia Commons

Chang’e-4 was launched on December 8 from the Xichang Satellite Launch Center in China’s Sichuan Province, carrying an aluminum, insulated biosphere of growing potatoes, Arabidopsis plant seeds, and a handful of silkworm eggs. The hope is that the biosphere will reveal how photosynthesis on the moon can work, providing insight for future moon farmers.

The mission landed Thursday in the Von Kármán Crater, and the spacecraft has been able to communicate with Earth so far via satellite. As the rover continues to roll over the snow-like terrain, it will measure the chemical composition of the soil, study cosmic rays, and observe the solar corona.

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