Abstract We investigate the thermal evolution of 3I/ATLAS, the third macroscopic interstellar object discovered on 2025 July 1. By comparing modeled thermal profiles with observations of volatile activity, it is possible to constrain bulk physical properties of a cometary nucleus. 3I/ATLAS is actively producing a variety of cometary volatiles. In this paper, we calculate one-dimensional thermal profiles of the third interstellar object 3I/ATLAS throughout its trajectory in an attempt to gain insight into its bulk properties based on measurements of its volatiles. Assuming a variety of typical comet and asteroid bulk geophysical properties such as heat capacities, densities, and conductivities, we calculate the radial thermal profile as a function of depth throughout the hyperbolic trajectory. The methods and code to generate the thermal profile are flexible for any hyperbolic or bound orbit. The thermal profiles are benchmarked to the nominal sublimation temperatures of H2O, CO2 and CO, but are still applicable to any volatile. Comparison between the modeled surface temperatures and the observed onset of H2O activity near 3 au indicates that surface temperatures exceeding ∼150 K can only be achieved if the albedo is below 0.2. We therefore set the upper limit on the albedo of 3I/ATLAS to be 0.2.
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