Brownian translation and rotation from the ballistic to the diffusive limit and derivation of the physical properties of dust agglomerates.

We analyzed the translational and rotational Brownian motion of aggregates of micrometer-sized silica spheres under microgravity conditions and in rarefied gas. The experimental data was collected in the form of high-speed recordings using a long-distance microscope as part of the ICAPS (Interactions in Cosmic and Atmospheric Particle Systems) experiment on board of the sounding rocket flight Texus-56. Our data analysis shows that the translational Brownian motion can be used to determine the mass and translational response time of each individual dust aggregate. The rotational Brownian motion additionally provides the moment of inertia and the rotational response time. A shallow positive correlation between mass and response time was found as predicted for aggregate structures with low fractal dimensions. Translational and rotational response times are roughly in agreement. Using the mass and the moment of inertia of each aggregate, we determined the fractal dimension of the aggregate ensemble. Slight deviations from the pure Gaussian one-dimensional displacement statistics were found in the ballistic limit for both the translational and rotational Brownian motion.