New secrets of the hidden side of the Moon. Yutu 2, the Chinese rover that landed on the other side of the Moon earlier this year, has just examined the first samples of the Moon’s mantle.
The samples are believed to have been excavated by a strong meteorite impact that crashed into the crust of the Moon, according to new research published in the journal Nature. With further study, these subsurface rocks could reveal once and for all how the Moon formed.
The researchers say that the Yutu-2 rover, deployed by the Chinese spacecraft Chang’e-4 that landed on the Moon in January, detected soil that appears rich in minerals and is believed to form the lunar mantle. We are getting closer to a more accurate view of the early development of the Earth’s natural satellite.
“Understanding the composition of the lunar mantle is key to determining how the moon formed and evolved,” says Mark Wieczorek, a geophysicist at the Côte d’Azur Observatory in Nice, France, who is not involved in the work. “We don’t have any clear and unaltered samples of the lunar mantle” from past lunar missions.
Hoping to find mantle samples, Chang’e-4 made landfall in the moon’s highest impact basin, the South Pole-Aitken basin. The collision that formed this huge hole is believed to be powerful enough to pierce through the lunar crust and expose the mantle rocks to the lunar surface. During its first day on the moon, Yutu-2 recorded the spectra of light reflected off the lunar soil at two different points using its visible and near-infrared spectrometer.
When the researchers analyzed these spectra, “what we saw was quite different from normal material on the lunar surface ,” says study co-author Dawei Liu, a planetary scientist at the Chinese Academy of Sciences at the National Astronomical Observatories in Beijing.
Yutu-2 spectra revealed a soil dominated by olivine and pyroxene with low calcium content, which are believed to be ingredients of the lunar mantle. One zone appeared to contain approximately 48% olivines and 42% low calcium pyroxene; only 10% represented a component of the lunar crust called pyroxene with high calcium content. The other place showed the following percentages: 55% olivine, 38% pyroxene low in calcium and only 7% pyroxene high in calcium.
“There should be more follow-up observations” to confirm that this material actually comes from the mantle, says Daniel Moriarty, a lunar geologist at NASA’s Goddard Space Flight Center in Greenbelt, who is not involved in the work. This is because other materials in the lunar crust, such as plagioclase, can create spectral signatures similar to olivine.
The most appropriate thing would be to bring samples back to Earth for laboratory analysis in order to distinguish the different mineral components.
According to the researchers, Yutu-2 will continue to investigate the Moon’s mantle candidate materials in preparation for a possible future sample return mission to Earth.
If it’s the mantle, the chemical composition of the material could help clarify the early history of the moon. According to experts, billions of years ago, the Moon was partially or completely molten. In its early days, the Moon would be a vast ocean of magma. As the moon cooled and solidified, materials of different densities separated into the mantle and crust. Samples of the lunar interior could help determine which models best describe how the moon evolved.
It could also shed light on planetary evolution in general because, unlike Earth, the Moon does not have tectonic plates that shuffle surface material or attract ocean water to the mantle when they slide under each other. The moon offers “a unique window” to the inner workings of a planetary body very different from our planet.
Referencia: Chang’E-4 initial spectroscopic identification of lunar far-side mantle-derived materials, Nature (2019). DOI: 10.1038/s41586-019-1189-0 , https://www.nature.com/articles/s41586-019-1189-0
Crédito imagen: NAOC/CNSA
