Erosion of Penitentes Under Experimental Conditions1Relevant to Ice-Covered Airless Worlds

The submeter-scale surface morphology of ice-covered worlds is poorly constrained by observations, but is important for understanding their physics and chemistry. In this experiment, we exposed pre-formed snow structures to temperature, pressure, and solar irradiance conditions similar to those on Europa and Enceladus. The sample consisted of 2-D sinusoidal penitente-like ridges, 2.5 cm tall with 1.25 cm spacing. Over one month at 165-175 K, and 10-4 Pa, the ridges decreased in height by 20% and became more triangular and less sinusoidal, evolving toward a more at surface. This despite the fact that the troughs appear brighter than the peaks, indicating focusing of light into the troughs. This suggests that penitentes are unlikely to be stable on airless worlds with free-molecular flow conditions, which is signicant for understanding the spectral and thermal properties of these worlds, and for understanding risks for future landed spacecraft.