A PLANETESIMAL AGGREGATION EXPERIMENT has been carried out in the low gravity environment of the Space Shuttle to test notions of how our solar system developed from a primordial cloud of micron sized dust particles. The experiment is the first direct re-creation, under realistic solar-nebula conditions, of the proposition that protoplanetary dust accumulates through sticky collisions amid the random Brownian motion of the particles. A consortium of German and US scientists (contact Jurgen Blum, University of Jena, Germany, 011-49-364-194-7515, blum@astro.uni-jena.de) observed that the dust quickly aggregates. The data bears out the main theory of planetesimal formation, but there was one surprise: the structures were expected to be somewhat fractal in nature, with a fractal dimension d of about 1.8, meaning that the mass of the cluster should be proportional to the cluster size raised to the d power. Instead the dimensionality turned out to be about 1.3, meaning the structures were observed to be more linear and less sheetlike (see figure at Physics News Graphics). (Blum et al., Physical Review Letters, 18 September /pnu/2000/; Select Article.)