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tokens: additionally with 10 6 , 10 6.5 , 10 7.5 , and 10 8 particles for convergence tests, plus 12 miscellaneous tests with 10 7 particles detailed in Section 3.3 . To be precise, these stated particle numbers refer to the number of particles per Earth mass (the bare target plus impactor mass is 1.02 M ⊕ ). Thus, the numerical resolution stays the same for simulations with different-mass planets. For example, a “10 7 ” simulation that includes a 0.1 M ⊕ atmosphere actually contains a total of ∼1.12 × 10 7 particles. For most of the suite we focus on the 10 −2 M ⊕ atmosphere. Figure 2 summarizes the parameters for each simulation. Note that the v c = 0.75 v esc scenarios would require some third body to have slowed down the impactor during its approach to below the mutual escape speed. This is unlikely in the case of primary impactors falling in to Earth in our solar system but is a useful test for the consequences of a highly grazing impact resulting in a large bound fragment that will re-impact at a later time. It also lets us compare with other models, which predict little erosion in this regime. Figure 2. Suite of simulation scenarios, arranged by their speed and impact parameter at contact (see Figure 1 and Appendix A ). As shown in the legend, the nested marker colors indicate the mass of the atmosphere (in Earth masses) for each simulation, while the line angles indicate the number of particles per Earth mass. At the high-speed end, given Earth’s position in the solar system, 5 v esc is around the highest typical velocity that might be expected for an impact (Raymond et al. 2009 ). For context, Earth’s orbital speed around the Sun is about 3 v esc . The suite’s extension to 8 v esc both allows us to test the extreme end of the parameter space and is a regime that could be more common in other planetary systems, for example, with a more massive star or a target planet deeper in the star’s potential well. Furthermore, in studies like that by Inamdar Schlichting ( 2015 ) where erosion is estimated as a function of the impactor’s momentum, using very high velocities will allow us to test the degeneracy between impactor mass and speed across a wide range of momenta in future suites with different impactor masses. For the relatively small impactor mass used here, even 8 v esc is not predicted by Inamdar Schlichting ( 2015 ) to remove more than 3/4 of the atmosphere. The simulations are run using SWIFT with a simple “vanilla” form of SPH plus the Balsara ( 1995 ) switch for the artificial viscosity as described in Kegerreis et al. ( 2019 ) to a simulation time of 100,000 s (roughly 28 hr) in a cubic box of side 80 R ⊕ to allow the tracking of ejecta. Any particles that leave the box are removed from the simulation. Throughout the first 10 hr we record snapshots every 100 s, for high time resolution during the impact and its immediate aftermath. To reduce data storage requirements, we then output snapshots every 1000 s for the remainder. 2.3.