Dynamical Simulation of the Interstellar Comet 3I/ATLAS

Abstract Comet 3I/ATLAS, also known as C/2025 N1, was discovered on 2025 July 1 UT by NASA Asteroid Terrestrial-impact Last Alert System (ATLAS), with a v ∞ ∼ 58 km s −1 . This is the fastest among the three interstellar objects discovered so far. In this work, we study the interaction of 3I/ATLAS with Mars preperihelion, and Jupiter postperihelion. We also present the results of the dynamical simulations of the orbital evolution of the comet for 100 yr in the past and future. For our analysis, we have used REBOUND, an N -body simulation package, to study these situations. We use the adaptive size mathematical integrator Ias15 , with a 1 day time step for long-term integration, and a 1 hr time step to study the effect of the planets on this body during the close encounters. We have seen an effect of Jupiter on the orbital parameters of the comet, which affects its postperijove trajectory significantly. The impact of Mars on this comet is minimal compared to the effect of Jupiter. This is consistent with the point that the comet moves well past Mars’s Hill radius but very close to Jupiter’s Hill radius at the respective close approaches. However, the effect of nongravitational forces will alter the results. Since the nongravitational forces are not yet known, we predict the variation of the orbital parameters considering a range of possible magnitudes of the nongravitational acceleration.