The Voyage of Complex Organic Matter: From the Protosolar Nebula to the Galilean Moons

The presence of carbonaceous material is inferred on the surfaces of numerous outer Solar System bodies, including the Galilean moons. Furthermore, the densities and moments of inertia of icy moons and dwarf planets suggest that such material may also be incorporated into their refractory cores. This carbonaceous component likely originated as complex organic molecules (COMs), possibly formed when the moons' building blocks - pebbles and icy grains - resided in the protosolar nebula. Laboratory experiments have shown that COMs can be formed by thermal processing or UV irradiation of icy grains under nebular conditions.

A leading scenario is that the Galilean moons formed in a circumplanetary disk that remained too cold to vaporize the solids inherited from the protosolar nebula. In this context, the thermodynamic conditions within the protosolar nebula are the primary factors controlling the composition of the moons' precursors. The goal of this study is to characterize the nebular conditions that allowed the formation and subsequent delivery of COMs to the Galilean moon-forming region under this cold disk scenario.

To this end, we have developed a two-dimensional Lagrangian model to simulate the transport of grains and dust particles during the evolution of the protosolar nebula. This approach allows us to compute the cumulative interstellar UV flux received by the particles as they migrate through the disk.

Using this particle tracking model, we analyze the UV flux and thermal history experienced by the grains. By comparing these values with laboratory derived thresholds for COM formation from NH3:CO2 ices, we identify the spatial and temporal windows in the disk where COM synthesis is possible. Finally, we assess whether the newly formed nitrogen-bearing COMs could have been transported to the Jovian region and ultimately incorporated into the building blocks of the Galilean moons.