Experimental results from the CoPhyLab – determination of the mass loss balance

Water is the driving force of life as we know it. Therefore, it is essential to study its properties and behaviour in various environments. In outer space, water occurs, e.g., in comets. Measurements on comets are challenging and expensive. Thus, it is easier to simulate the environment of outer space in the laboratory.One laboratory where this environment can be simulated is the Comet Physics Laboratory (CoPhyLab) at the TU Braunschweig. Outer space is simulated with a thermal vacuum chamber enabling pressures as low as 10−6mbar and temperatures of around 100 K. Insolation, either permanent or following a diurnal cycle, can be simulated via a focused halogen lamp and rotating shutter blades. With this setup, the most abundant ingredients of comets, i.e. granular water ice and dust, can be studied in their natural environment and repetitive measurements can be performed.One observed property of comets, which is not yet fully understood on a physical basis, is the ejection of dust particles due when approaching the sun. In the CoPhyLab, this dust activity can be quantitatively measured by the difference of total mass loss and mass loss by ice sublimation alone. The latter can be measured with a mass spectrometer and can, furthermore, be inferred from the surface temperature measured by an infrared camera and using the Hertz-Knudsen equation for the sublimation of water ice. The total mass loss of the sample on the other hand can either be measured by using a scale or by measuring the shrinking volume of the sample via a line laser system. The combination of all instruments determines the ratio of mass loss in gas and particles and its evolution over time.The latest results on the dust and gas activity of granular ice samples under different illumination conditions will be presented, from which ideas of the enigmatic dust-emission mechanism can be formulated.