The Production of Dust-Ice-Pebbles

<p>In the CoPhyLab at the TU Braunschweig, the goal is to simulate the physical behaviour of comets on Earth. Therefore, we are currently producing pebbles from silicate dust and water ice in order to subsequently investigate their properties and behaviour in various experiments. The pebbles we are producing consist of a mixture of water ice and dust, but also of pure water ice.</p> <p><img src="" alt="" /></p> <p><em>Figure 1: Sieved pebbles with diameters of 1mm to 1.6mm consisting of a mixture of dust and water ice with a ratio 3:1.</em></p> <p>The materials are mixed and then shaken while low temperatures are secured. For a homogenous mixture some nitrogen is added during the mixing procedure. In order to be able to form the largest possible number of pebbles from a mixture, it is necessary to understand the process of pebble formation. Therefore, we have studied the formation behaviour of pebbles from mixtures with different mixing ratios and by using different shaking techniques. Recent experiments have shown that mixtures with different weight ratios of dust-to-water ice can form pebbles. Also, adding a certain amount of graphite to darken the mixture has no effect on the formation process.</p> <p>To study and to quantify the properties of the pebbles, such as compressive strength and thawing behaviour, it is important to know the particle size distribution. For this purpose, the pebbles must be sieved. This has been successfully carried out at the TU Braunschweig. With the samples obtained in this way, it has already been possible to gain initial insights into, among other things, the thawing behaviour and porosity of the pebbles. It was found, for example, that pebbles with an higher dust content retain their structure and a baking effect occurs, which leads to a hardening of the material, whereas pebbles with a low dust content collapse.</p> <p>During this conference we will present our pebble making technique and our findings about the formation of pebbles. Further, we want to introduce the audience to our shaking machine. The latest results about the thawing behaviour as well as other properties of the pebbles will be presented, too. </p>