  Cometary dust particles are remnants of the primordial accretion of
refractory material that occurred during the initial stages of the Solar System
formation. Understanding their physical structure can help constrain their
accretion process. We have developed a simple numerical simulation of aggregate
impact flattening to interpret the properties of particles collected by COSIMA.
The aspect ratios of flattened particles from both simulations and observations
are compared to differentiate between initial families of aggregates
characterized by different fractal dimensions $D_f$. This dimension can
differentiate between certain growth modes. The diversity of aspect ratios
measured by COSIMA is consistent with either two families of aggregates with
different initial $D_f$ (a family of compact aggregates with fractal dimensions
close to 2.5-3 and some fluffier aggregates with fractal dimensions around 2).
Alternatively, the distribution of morphologies seen by COSIMA could originate
from a single type of aggregation process, such as DLPA, but to explain the
range of aspect ratios observed by COSIMA a large range of dust particle
cohesive strength is necessary. Furthermore, variations in cohesive strength
and velocity may play a role in the higher aspect ratio range detected (>0.3).
Our work allows us to explain the particle morphologies observed by COSIMA and
those generated by laboratory experiments in a consistent framework. Taking
into account all observations from the three dust instruments on-board Rosetta,
we favor an interpretation of our simulations based on two different families
of dust particles with significantly distinct fractal dimensions ejected from
the cometary nucleus.
