Dusty Mafic Rocks Alone the Path of Chang'E-4 Rover: Initial Analysis of the Image Cubes of the Onboard Visible and Near-Infrared Imaging spectrometer

The Yutu-2 rover of Chang'E-4 encountered four special rocks along its path. The onboard Visible and Near-infrared Imaging Spectrometer (VNIS) collected their spectral data at close range. In this work, we focus on the visible/near-infrared image cubes captured by the VNIS. Simple classification was performed using the K-means algorithm based on the 750/900 nm spectral ratios to highlight the surface material variations. In the case of narrow measurements of phase angle, the classification results were not significantly affected by viewing geometry. Varying degrees of dust coverage on the rock surfaces were revealed, which may be attributed to ejecta deposition and dust electrostatic levitation. The spectral shapes of the less dust-covered surfaces indicated that these rocks are dominated by mafic materials, suggesting they may not originate from the lunar upper crust. The influence of dust coverage on spectral measurement of rocks was also confirmed, which significantly attenuates the absorption depths. Plain Language Summary The Chang'E-4 (CE-4) mission is the first probe to successfully land on the lunar farside. The rover of CE-4 mission, Yutu-2, has come across four curious rocks during its exploration. To reveal their compositions, Yutu-2 rover conducted close investigations and captured their spectral images using the onboard Visible and Near-infrared Imaging Spectrometer instrument (VNIS). We analyzed these data and found an interesting phenomenon that these rock surfaces are partly covered by lunar dust. Dust coverage obscures the information from the rocks themselves, making it difficult to decipher the rock compositions if not carefully handled. Fortunately, benefiting from the spatial insight provided by the VNIS, we analyzed the areas with less dust coverage on rock surfaces and determined that these rocks are likely dominated by mafic materials, suggesting that they may not originate from the lunar upper crust.

Automated summary

The Yutu-2 rover of the Chang'E-4 mission encountered four special rocks during its exploration. The onboard VNIS collected their spectral data and revealed varying degrees of dust coverage on the rock surfaces. The analysis suggests that these rocks may not originate from the lunar upper crust.