Experimental results from the CoPhyLab - Particle activity of Dust-Ice mixtures under horizontal illumination

When comets approach the Sun, sublimation of ice releases dust particles, forming a coma and tail. To reproduce this activity in the laboratory, CoPhyLab experiments employ granular water ice or ice–dust mixtures in a thermal vacuum chamber, illuminated from above. While pure ice samples exhibit continuous particle ejection until complete sublimation, dust–ice mixtures cease activity after a brief period, unlike real comets. We attribute this to gravitational redeposition of dust, which builds an insulating surface layer and shuts down sublimation. To overcome this, we rotate the experimental assembly by 90° so that illumination is delivered from the side. In this geometry, ejected grains no longer fall back onto the sample, sustaining continuous activity. Preliminary tests with ice–silica and ice–graphite mixtures confirm prolonged particle ejection. These results demonstrate a simple method to mimic sustained cometary dust activity and will help interpret observations of cometary dust environments and the influence of the ice to dust ratio.