Assessment of the Mass Loss and Radius Change of 3I/ATLAS Based on Observed Production Rates

Abstract

Formed from the debris of planet formation, interstellar comets provide invaluable insights into the chemical compositions of planetary systems outside of our Solar System. Spectroscopic observations of 3I/ATLAS, the third interstellar object, reveal production of numerous volatiles and refractory species throughout its trajectory. In this paper we present a framework to calculate the change in radius of an object on an arbitrary trajectory at any point in its orbit, applicable to any small body experiencing mass-loss. We next provide a comprehensive, machine readable table containing volatile and refractory production rates from all reported observations of 3I/ATLAS pre- and post-perihelion. Applying these equations to 3I/ATLAS, we calculate that it has lost $\sim$ 1.28-5.53 meters of its surface during its passage through the Solar System from gas alone, corresponding to $\sim$ 10$^9$-10$^{10}$ kg and $\sim$ 0.12-0.53 % of its total mass. Considering dust-to-gas ratios from 1-4, we estimate surface erosion down to depths $>$10 meters. We present these calculations as approximations based on discontinuous observational data with varying methodology and instrumentation. We also estimate contributions from detected parent molecules separate from the daughter products of photodissociation. Conservative and optimistic estimates were calculated over a range of heliocentric distances defined by the onset of activity in reported observations and the typical onset of sublimation distance for each species, respectively. The reported production rates combined with the change in radius calculation can be used to estimate subsurface locations of various species within the nucleus of 3I/ATLAS.