Exploration

Chinese Lunar Rover Sleeps After Rolling on Far Side of the Moon

China is the first to successfully land an explorer on the side of the moon that never faces Earth.

After making history by becoming the first nation to land on the far side of the moon, China’s new spacecraft  transmitted haunting pictures back to Earth of this mysterious lunar landscape as its rover began to explore the surface. And then the rover took a nap. 

The spacecraft includes a lander called Chang’e-4 and a rover called Yutu-2. The ground mission has gone well so far, the China National Space Administration reported, with the successful deployment of instruments to analyze radiation and low-frequency radio waves, as well as some stunning snapshots using the onboard cameras.

While other spacecraft orbiting the moon have observed the half of it that never faces Earth, China is the first to have successfully landed an explorer on the surface for close inspection. The photos released by the China National Space Administration show the rover exiting the lander to begin its expedition.

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Though sometimes characterized as the moon’s “dark side,” the far side actually receives as much light as the opposite hemisphere: two weeks of sunlight followed by two weeks of darkness.

As Chang’e-4 continues performing tests, Yutu-2 has entered standby mode for a few days to avoid “high noon,” a period where the sun gets high in the sky above the moon, sending temperatures on the surface soaring beyond the boiling point of water on Earth — 260 degrees Fahrenheit or 127 degrees Celsius. It is expected to emerge from their slumber on Jan. 10.

CSNA, Chang'e 4, Yutu 2, far side of the moon
CNSA

It’s an exciting moment for China, which executed the unprecedented landing in early January. Because the far side of the moon permanently faces space opposite to Earth, scientists would hear nothing from the surface unless they could use a relay satellite to send signals home from the moon. China is sending back its data with such a satellite, called Queqiao.

Also riding aboard the rover is a Swedish instrument called Advanced Small Analyzer for Neutrals (ASAN). It’s designed to look at how the solar wind — the constant stream of charged particles emanating from the sun — may change the lunar surface and produce water. Solar particles carry radiation to the moon’s surface, which may explain why the lunar dust looks so weathered.

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“The lunar surface is covered by a fine-grained material, regolith,” wrote Martin Wieser, the principal investigator for ASAN, in an email to Seeker.

He explained that the regolith shows wear and tear when protons, or positively charged particles, hit the surface after emanating from the sun. Unlike Earth, the moon lacks a magnetic shield, called a magnetosphere, to stop the radiation from reaching the surface. This means that the regolith receives and then absorbs the radiation. The radiation sets off a chain reaction in the regolith that could produce water, scientists suppose, but ASAN will help show that for sure.

CNSA, Chang'e 4, Yutu 2, far side of the moon
CNSA

The Yutu-2 rover follows on from the successful Indian Chandrayann-1 mission, which was among the first spacecraft to show evidence of water on the moon after mapping the surface between 2008 and 2009. An instrument from Sweden called SARA (which bears the complicated acronym “Sub KeV Atom Reflecting Analyzer”) mapped this radiation flux from the surface. Scientists got a sense of how the radiation operates around the moon, Wieser said, but what’s missing are calibrations from the surface to validate the measurements from orbit.

The far side is exciting for another reason, Wieser explained.

“The far side of the moon is much more exposed to the solar wind than the near side for geometrical reasons,” he wrote. “When the near side is illuminated by the sun, then the moon is inside the Earth’s magnetosphere, where the solar wind is screened away.”

In other words, the far side of the moon receives more radiation than the near side because the far side is less shielded.

Yutu-2 operates in a strange magnetic environment courtesy of its landing site, the South Pole-Aitken basin. The basin includes one of the largest craters in the entire solar system. The basin also has a local strong magnetic field, which influences how the solar wind interacts with the surface. But exactly how it influences this interaction is something Swedish scientists want to know — and for that reason, they want Yutu-2 to last as long as it can. (Its current estimated lifetime is a year.)

Sweden is very active in the field of space radiation, including on the European Bepi-Colombo mission that recently launched to Mercury. Mercury, like the moon, is an “airless” world that is full of regolith and craters. So studying the two worlds will give scientists some comparisons to see how similarly (or differently) the radiation environment works on the moon and on Mercury.

Chang’e-4 is the latest in a series of Chinese missions to explore the moon. The last took place in 2013, when Chang’e-3 and its rover, Yutu, made the first successful lunar rover excursion in a generation.