4:30 PM - 4:45 PM
[PPS08-23] Boulder tracks on the moon: insights into the mechanical properties of surface regolith
Keywords:moon, regolith, volatile, boulder track
Theoretically, permanently shadowed regions (PSRs) in the lunar polar regions have been suggested as long-term traps for water molecules delivered to the lunar surface. Past observations have also suggested the presence of such water deposits. However, due to the lack of sufficient sunlight within PSRs, acquiring high-spatial-resolution spectroscopic data to directly analyze material composition remains challenging. Therefore, landing exploration missions are progressing rapidly to obtain highly precise data. At the same time, understanding the horizontal distribution of water ice is equally important, which requires remote sensing for large-scale exploration and the development of new methods for detailed observations within PSRs under limited sunlight conditions.
Recently, the ultra-sensitive ShadowCam onboard the Danuri spacecraft successfully captured high-resolution images of PSR interiors for the first time. Observations of the lunar south pole region using these images have revealed many boulder tracks, which are the traces of rock masses that have moved. The spacing and morphology of the tracks are said to vary according to parameters such as the motion patterns of falling rocks and the mechanical properties of the slope, based on observations and experiments on Earth. In other words, understanding the differences in track characteristics on the lunar surface is important for understanding the kinematics of boulders on the Moon and the mechanical properties of the regolith covering the lunar surface. In particular, the latter may be a key factor in constraining the likely water ice coverage in the PSR.
In this study, we statistically analyze the locations and morphologies of boulder tracks in the lunar south pole region using ShadowCam images. We will then reproduce these observations numerically using the Discrete Element Method (DEM) to constrain the mechanical properties of lunar surface materials. This approach will also provide insight into the regions where water ice is present.
Boulder tracks were mapped using ShadowCam high-resolution images (1.7 m/pix) of the entire Shackleton crater area, revealing a total of 22 tracks, up to 7 km in length. Track morphology varied by location and could be categorized into two primary types based on aspect ratio. In some areas, aspect ratios were found to vary within individual tracks. Furthermore, numerical simulations confirmed that boulder track morphology is influenced by the velocity of falling rocks. In addition, variations in the coefficient of friction, which reflect differences in the constituent materials determining mechanical properties, also affect the aspect ratio of the tracks. As a result, future large-scale observations of boulder tracks may offer valuable insights into the distribution of water ice on the lunar surface.
Recently, the ultra-sensitive ShadowCam onboard the Danuri spacecraft successfully captured high-resolution images of PSR interiors for the first time. Observations of the lunar south pole region using these images have revealed many boulder tracks, which are the traces of rock masses that have moved. The spacing and morphology of the tracks are said to vary according to parameters such as the motion patterns of falling rocks and the mechanical properties of the slope, based on observations and experiments on Earth. In other words, understanding the differences in track characteristics on the lunar surface is important for understanding the kinematics of boulders on the Moon and the mechanical properties of the regolith covering the lunar surface. In particular, the latter may be a key factor in constraining the likely water ice coverage in the PSR.
In this study, we statistically analyze the locations and morphologies of boulder tracks in the lunar south pole region using ShadowCam images. We will then reproduce these observations numerically using the Discrete Element Method (DEM) to constrain the mechanical properties of lunar surface materials. This approach will also provide insight into the regions where water ice is present.
Boulder tracks were mapped using ShadowCam high-resolution images (1.7 m/pix) of the entire Shackleton crater area, revealing a total of 22 tracks, up to 7 km in length. Track morphology varied by location and could be categorized into two primary types based on aspect ratio. In some areas, aspect ratios were found to vary within individual tracks. Furthermore, numerical simulations confirmed that boulder track morphology is influenced by the velocity of falling rocks. In addition, variations in the coefficient of friction, which reflect differences in the constituent materials determining mechanical properties, also affect the aspect ratio of the tracks. As a result, future large-scale observations of boulder tracks may offer valuable insights into the distribution of water ice on the lunar surface.