Comet formation in the framework of streaming instability

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The solar system's bodies formed 4.6 billion years ago in a protoplanetary disk around the young protosun, starting from submicrometre-sized dust and ice grains. Through collisions and coalescence, these grains evolved into aggregates, planetesimals, and ultimately planets. Comets are thought to be the kilometre-sized icy planetesimals that did not merge into larger bodies and have persisted to this day. However, the process by which bodies grow beyond millimetre to decimetre sizes is not well understood, as bouncing and fragmentation typically halt growth before reaching kilometre scales. A promising mechanism, streaming instability, arises from the interaction between gas and dust aggregates, leading to high local dust densities that collapse under self-gravity to form planetesimals ranging from kilometres to a few hundred kilometres. This mechanism predicts characteristics typical of comets. The research explores comet formation through the lens of streaming instability, modelling aggregate growth in the solar nebula to identify the properties that trigger this instability. Additionally, simulations of a porous aggregate cloud's gravitational collapse are conducted to investigate changes in aggregate properties during collapse and to determine if the resulting planetesimal exhibits comet-like characteristics.