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Aggregation experiments with magnetized dust grains

H. Nübolda*, T. Poppeb and K.-H. Glassmeiera aInstitut für Geophysik, TU Braunschweig, Mendelssohnstr. 3, D-38106 Braunschweig, Germany, Email: [email protected]

bAstrophysikalisches Institut der Universiät Jena, Schillergäßchen 2-3, D-07745 Jena, Germany

The growth of fractal aggregates from small dust grains is believed to be the first step in the formation process of planetesimals and cometesimals. The grain-grain interactions treated up to now were mainly of mechanical and electrostatic nature. However, there is evidence that magnetic interactions between permanently magnetized dust grains could have played an important role in the aggregation process. We prepared aggregation experiments with micron-sized magnetized dust analogues in a dilute gas. In this paper, we describe a feasibility study on the use of the magnetized dust in existing experimental facilities. First results are presented.

I. INTRODUCTION

The formation of macroscopic objects in the early Solar System is generally believed to have been initiated by collisional growth of dust aggregates from micron-sized grains. This mechanism has replaced gravitational instability as the 'standard' way of assembling planetesimals in the solar nebula, since it has been shown, that turbulence should inhibit the formation of a dust layer dense enough to become gravitationally unstable [1], On the other hand, today's picture of preplanetary dust aggregation is far from being complete. The problem of how collisional grain growth could proceed fast enough to create the building blocks of our Solar System within the relatively short period of 106 — 107 years [2] remains to be solved. The very first stage of the aggregation process produces fluffy clusters of fractal nature. How and when does compaction toward more massive objects occur [3]? These are just a few considerations showing that preplanetary dust aggregation deserves further study.

Up to now, preplanetary dust aggregation scenarios mainly included mechanical (surface) interactions between dust particles [4,5]. Few authors considered long ranged interactions: Ossenkopf [6] as well as Horanyi and Goertz [7] discussed electrostatic interactions between charged grains, Nuth et al. [9] performed experiments with small magnetic iron particles. We believe that the latter deserves additional attention since magnetic interactions between magnetized grains add a some interesting features to the dust aggregation process. To this end, we assume that a magnetizable dust population was present in the

'supported by the Studienstiftung des deutschen Volkes through their PhD-program.

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