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.