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We carry out three-dimensional Smoothed Particle Hydrodynamics simulations ofspherical homogeneous SiO2 dust aggregates to investigate how the mass and theporosity of the aggregates affects their ability to survive an impact atvarious different collision velocities (between 1 - 27.5m/s). We explore howthe threshold velocities for fragmentation vary with these parameters.Crucially, we find that the porosity plays a part of utmost importance indetermining the outcome of collisions. In particular, we find that aggregateswith filling factors >37% are significantly weakened and that the velocityregime in which the aggregates grow is reduced or even non-existent (instead,the aggregates either rebound off each other or break apart). At fillingfactors less than ~37% we find that more porous objects are weaker but not asweak as highly compact objects with filling factors >37%. In addition we findthat (for a given aggregate density) collisions between very different massobjects have higher threshold velocities than those between very similar massobjects. We find that fragmentation velocities are higher than the typicalvalues of 1m/s and that growth can even occur for velocities as high as27.5m/s. Therefore, while the growth of aggregates is more likely if collisionsbetween different sized objects occurs or if the aggregates are porous withfilling factor <37%, it may also be hindered if the aggregates become toocompact.

Growth and fragmentation of centimetre-sized dust aggregates: the dependence on aggregate size and porosity