5:15 PM - 7:15 PM
[PPS06-P13] Laboratory simulations of rock weakening and regolith formation on asteroids due to heating
Keywords:regolith, boulder, thermal stress, asteroid
The surfaces of the Moon and asteroids are covered by a sedimentary layer called regolith, which consists of fine sand and dust. Regolith primarily forms through rock fragmentation caused by impacts from meteoroids, as well as crack growth caused by thermal stresses. Understanding the process and rate of regolith formation is important for clarifying the surface evolution of these bodies. In this study, to deepen our understanding of regolith formation, we focus on thermal stress and investigate its role in rock fracturing by creating simulated rocks on asteroids.
The prepared blocks were cylindrical specimens made by mixing gypsum, sand, and water in a ratio of 10:10:7 and drying them at 100 °C. The porosity of the blocks was about 40 %, the radius was about 20 mm, and the thickness was about 11 mm. Multiple blocks were produced and used for the experiments. The blocks were heated in a high-temperature furnace to observe whether cracks formed and how their strength changed. To assess crack formation, the longitudinal wave velocity of the blocks was measured before and after heating, and the change in velocity was used to determine the extent of fracturing progressed. Strength was measured using a crushing tensile test. Experiments were conducted under various heating conditions, with temperatures from 200 °C to 300 °C and durations from 10 minutes to 20 hours. The obtained data were then compared.
The results obtained from the experiment showed that the higher the exposure temperature, the lower the longitudinal wave velocity. In other words, more cracks formed in the block. Additionally, the longer the exposure time at high temperatures, the lower the longitudinal wave velocity. The strength was also found to decrease along with the longitudinal wave velocity. The longitudinal wave velocity of the block heated at 270 °C for 20 hours decreased to about 0.7 times its original value. After heating at 270 °C for 30 minutes, the longitudinal wave velocity was reduced to about 0.9 times its initial value. When heated at 300 °C for 20 hours, the blocks became brittle and crumbled into powder upon touch. The experiments conducted simulated rock fracturing on a hydrous asteroid with a surface temperature of about 550 K and a distance from the Sun of about 0.6 au, leading to a better understanding of the duration and temperature scale at which fracturing occurs on the asteroid.
The prepared blocks were cylindrical specimens made by mixing gypsum, sand, and water in a ratio of 10:10:7 and drying them at 100 °C. The porosity of the blocks was about 40 %, the radius was about 20 mm, and the thickness was about 11 mm. Multiple blocks were produced and used for the experiments. The blocks were heated in a high-temperature furnace to observe whether cracks formed and how their strength changed. To assess crack formation, the longitudinal wave velocity of the blocks was measured before and after heating, and the change in velocity was used to determine the extent of fracturing progressed. Strength was measured using a crushing tensile test. Experiments were conducted under various heating conditions, with temperatures from 200 °C to 300 °C and durations from 10 minutes to 20 hours. The obtained data were then compared.
The results obtained from the experiment showed that the higher the exposure temperature, the lower the longitudinal wave velocity. In other words, more cracks formed in the block. Additionally, the longer the exposure time at high temperatures, the lower the longitudinal wave velocity. The strength was also found to decrease along with the longitudinal wave velocity. The longitudinal wave velocity of the block heated at 270 °C for 20 hours decreased to about 0.7 times its original value. After heating at 270 °C for 30 minutes, the longitudinal wave velocity was reduced to about 0.9 times its initial value. When heated at 300 °C for 20 hours, the blocks became brittle and crumbled into powder upon touch. The experiments conducted simulated rock fracturing on a hydrous asteroid with a surface temperature of about 550 K and a distance from the Sun of about 0.6 au, leading to a better understanding of the duration and temperature scale at which fracturing occurs on the asteroid.