11:00 AM - 1:00 PM
[MIS17-P01] Experimental study related to impact phenomena on habitable planets: High-velocity impact experiments on wet sand targets under atmospheric pressure
Keywords:Habitable planets, Wet quartz sand, High-velocity impact experiments, Impact-generated vapor clouds, Impact crater
A habitable planet is characterized by the presence of liquid water on its surface, like the Earth. Mars is also one of the planets that would be covered with liquid water on its surface in the past, and a recent study reported that water vapor was observed in the upper atmosphere [1]. Since the Martian atmospheric pressure is about 600Pa, which is cloth to the triple point pressure of water, water vapor is transported to the poles by atmospheric circulation and then snowfall and evaporation may be locally balanced. In fact, evidence of liquid water has been found in the polar caps [2].
Many impact craters are observed on the surface of planets including Mars, and they have a wide variety of their shapes and sizes. A rampart crater found on Mars is one of the features characterized by fluidized ejecta, and its formation process could be affected by subsurface water and ice [3]. However, it is now well known how the crater formation processes on the wet surface are affected by the subsurface water.
Then, we conducted high-velocity impact experiments on the wet surface composed of quartz sand with various contents of water under Martian atmospheric pressure, and studied the effects of liquid water on the crater formation process and the mechanisms of water vapor release process by impact. Our study might clarify the effects of high-velocity impacts on the topography and atmosphere of habitable planets such as Earth and the past Mars.
Impact experiments were conducted using a horizontal two-stage light gas gun at Kobe University. Aluminum projectiles with the diameter of 2mm was launched at 2 and 4 km/s on wet sand targets with the water contents of 0-12wt.%. The target surface inclined at 30° from the horizontal plane. All the experiments were conducted at the room temperature of 20°C and the vacuum condition of 600-800Pa; it allows liquid water existence in the target. Each experiment was observed by high-speed cameras taken at 1.0×105 fps from two different directions.
High-speed jetting and plasma expansion due to the evaporation of projectile was observed toward the impact direction at the impact. In addition, a white plume was also observed to be ejected vertically above the target surface. This plume may be a cloud of condensed water vapor evaporated from the impact point. However, a crater shape similar to the rampart crater was not observed.
The penetration strength of the target surface, measured by uniaxial compression tests, increased with the increase of the water contents from 0% to 12%. This result suggests that the crater growth would be suppressed with increasing the water contents and the crater diameter decreases with the water contents. It was found that the crater diameters of both final and transient craters decreased by 30-50% with the increase of the water content of up to ~6%, and then increased by ~20% with the increase of the water content of up to ~12%. This result could suggest that the crater diameter decreases due to the increase of apparent frictional force with increasing water content. But above the water content of ~6%, liquid water among sand grains may reduce the shock wave attenuation, and it helps to keep the strong shock pressure far away and to increase the crater diameter.
References [1]Fedorova, et al. (2020), Science 367, 297-300. [2]Orosei, et al. (2018), Science 361, 490-493. [3]Suzuki and Kurita. (2016), Journal od Geography 125(1), 13-33.
Many impact craters are observed on the surface of planets including Mars, and they have a wide variety of their shapes and sizes. A rampart crater found on Mars is one of the features characterized by fluidized ejecta, and its formation process could be affected by subsurface water and ice [3]. However, it is now well known how the crater formation processes on the wet surface are affected by the subsurface water.
Then, we conducted high-velocity impact experiments on the wet surface composed of quartz sand with various contents of water under Martian atmospheric pressure, and studied the effects of liquid water on the crater formation process and the mechanisms of water vapor release process by impact. Our study might clarify the effects of high-velocity impacts on the topography and atmosphere of habitable planets such as Earth and the past Mars.
Impact experiments were conducted using a horizontal two-stage light gas gun at Kobe University. Aluminum projectiles with the diameter of 2mm was launched at 2 and 4 km/s on wet sand targets with the water contents of 0-12wt.%. The target surface inclined at 30° from the horizontal plane. All the experiments were conducted at the room temperature of 20°C and the vacuum condition of 600-800Pa; it allows liquid water existence in the target. Each experiment was observed by high-speed cameras taken at 1.0×105 fps from two different directions.
High-speed jetting and plasma expansion due to the evaporation of projectile was observed toward the impact direction at the impact. In addition, a white plume was also observed to be ejected vertically above the target surface. This plume may be a cloud of condensed water vapor evaporated from the impact point. However, a crater shape similar to the rampart crater was not observed.
The penetration strength of the target surface, measured by uniaxial compression tests, increased with the increase of the water contents from 0% to 12%. This result suggests that the crater growth would be suppressed with increasing the water contents and the crater diameter decreases with the water contents. It was found that the crater diameters of both final and transient craters decreased by 30-50% with the increase of the water content of up to ~6%, and then increased by ~20% with the increase of the water content of up to ~12%. This result could suggest that the crater diameter decreases due to the increase of apparent frictional force with increasing water content. But above the water content of ~6%, liquid water among sand grains may reduce the shock wave attenuation, and it helps to keep the strong shock pressure far away and to increase the crater diameter.
References [1]Fedorova, et al. (2020), Science 367, 297-300. [2]Orosei, et al. (2018), Science 361, 490-493. [3]Suzuki and Kurita. (2016), Journal od Geography 125(1), 13-33.