Fragmentation Dynamics of Pristine Interstellar Comets: An Exploratory Multi-Physics Simulation Study

We present an exploratory numerical model for the thermal evolution and fragmentation of pristine interstellar comets during a first passage through the inner Solar System, and we apply it across a grid of perihelion distances (q=0.25--1.5 AU) and tensile strengths (σ t=50--500 Pa). The model follows a single nucleus (M 0=2 times10 12 kg, R 0 about1060 m, dust/ice =1, ice composition 35% CO, 30% CO 2, 15% CH 4, 20% H 2O) along a continuous hyperbolic trajectory, solving heat conduction into an initially 30 K interior, energy-balanced multi-species sublimation with retreating volatile fronts, dust lifting and lag-mantle growth, and a subsurface gas-pressure failure criterion, so that the number of fragments is an emergent outcome rather than a numerical input. In our primary case (q=1 AU, σ t=100 Pa) the nucleus begins splitting essentially at the 3 AU start of the simulation (r h= 2.99 AU within the first day), as soon as a sub-millimeter lag deposit partially confines the warming CO front---implying that for pristine composition the onset lies beyond our starting distance---and disaggregates through 63 binary splittings into at least 64 fragments---our tracking cap, reached near perihelion after a self-limited pre-perihelion plateau at 53 bodies---with 1.3% total mass loss; sublimation is energy-limited, so reservoir depletions stay modest (CO 2%, CH 4 2%, CO 2 1%, H 2O <0.1%) and the shattered body retains almost all of its mass as a fragment swarm; the mass budget closes to machine precision. Across the explored grid, no combination leaves the nucleus intact, and mass loss depends only weakly on q and σ t (0.8--1.7%) while depending strongly on composition: depleted, 67P-like ices reduce mass loss to 0.1% at q=1 AU.