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

Abstract

We present an exploratory numerical model for the thermal evolution and fragmentation of pristine interstellar comets on a first passage through the inner Solar System, applied over a grid of perihelion distances ($q=0.25$--$1.5$~AU) and tensile strengths (${\sigma }_t=50$--$500$~Pa). A single nucleus ($M_0=2\times 10^{12}$~kg, $R_0\approx 1.06$~km, dust/ice $=1$, ices 35\% CO, 30\% CO${}_2$, 15\% CH${}_4$, 20\% H${}_2$O) follows a hyperbolic trajectory from an initially 30~K state, with heat conduction, energy-balanced multi-species sublimation, dust lifting and lag-mantle growth, and a subsurface gas-pressure failure criterion, so that fragmentation is emergent rather than prescribed. In the primary case ($q=1$~AU, ${\sigma }_t=100$~Pa) splitting begins at the 3~AU starting distance, once a sub-millimeter lag deposit partially confines the warming CO front; 63 binary splittings follow, with a self-limited plateau at 53 bodies before perihelion and the 64-body tracking cap reached near perihelion. Sublimation is energy-limited: total mass loss is 1.3\%, volatile depletions are at most a few per cent, and most of the mass survives as a fragment swarm; the mass budget closes to machine precision. Across the grid, mass loss (0.8--1.7\%) depends weakly on $q$ and ${\sigma }_t$ but strongly on composition, falling to 0.1\% for depleted, 67P-like ices. Yet every case, including the depleted class, disaggregates, whereas Jupiter-family comets of similar composition survive repeated perihelia, so the sealing prescription over-fragments. We regard the composition ranking, the insensitivity to ${\sigma }_t$, percent-level mass loss, and an onset beyond 3~AU as robust, and defer absolute survival predictions to calibration against well-observed comets. Mantle insulation suppresses outbound activity, producing an inbound--outbound asymmetry.

arXiv comment12 pages, 3 figures