Composition of a gleaming, “gel-like” strange substance discovered on the other side of the moon revealed


Impact Melt Gap and surrounding context

Figure 1. Impact fusion gap and surrounding context. Credit: CNSA, CLEP and AIR

The unusual glowing dark greenish-green substance in a crater on the other side of the moon has sparked widespread interest after its discovery by the Chang’e-4 rover in July 2019.

A research team led by Prof. DI Kaichang of the China Academy of Sciences Aerospace Information Research Institute (AIR) and his collaborators analyzed the substance in detail using multiple datasets from the mobile’s panoramic camera. (Pancam), risk prevention camera (Hazcam), and the visible and near infrared spectrometer (VNIS).

The researchers found that the unusual substance is actually an impact fusion gap, and the provenance of the rover measured around the regolith could originate from a differentiated fusion group or set of igneous rocks. Their findings were published in Letters of the Earth and Planetary Science.

Lunar Impact Meltdown Gap Samples

Figure 2. Photos of samples of lunar impact fusion gaps. Credit: NASA and AIR.

China’s Chang’e-4 probe, which includes a lander and a rover, successfully landed inside the 185-kilometer-wide Von Kármán crater within the South Pole-Aitken (SPA) basin on January 3, 2019, making the first squishy to be landing on the far lunar side.

The gelatinous substance was discovered in a crater (Fig. 1) during the eighth lunar day of the rover mission. Detailed measurements of the gap and the surrounding regolith were made during the ninth lunar day.

The discovered gap, measuring 52 by 16 centimeters, resembles the lunar impact melt gap samples 15466 and 70019 (Figure 2) returned by the Apollo missions. It was formed by welding generated by impact, cementing and agglutination of lunar regoliths and gaps.

Hazcam images show rover locations

Figure 3. Hazcam images show the location of the rover. Credit: CNSA, CLEP and AIR

The lumps surrounding the crater that houses the gap were crushed into regolith powder by the wheels of the scout vehicle (Figure 3), indicating that the regolith may compact slightly and become blocked and friable. The spectral disintegration results based on the Hapke model showed that plagioclase was abundant and that pyroxene and olivine had almost equal fractions, indicating that regolith was probably the product of erosion of noritic rocks.

The regolith measured by the Chang’e-4 rover was actually a mixture of multiple sources, with ejections from the Finsen crater being primary and possible contributions from the Alder crater. The Finsen and Alder craters are on the fringes of the proposed impact fusion group produced by the SPA basin formation event. Therefore, the provenance of the regolith could originate from a differentiated fusion group or a set of igneous rocks.

Reference: “Impact fusion gap and surrounding regolith measured by Chang’e-4 rover” by Sheng Gou, Zongyu Yue, Kaichang Di, Jia Wang, Wenhui Wan, Zhaoqin Liu, Bin Liu, Man Peng, Yexin Wang, Zhiping He and Rui Xu, June 8, 2020, Letters of Earth and Planetary Science.
DOI: 10.1016 / j.epsl.2020.116378