Non-thermal escape on Triton driven by atmospheric and ionospheric chemistry

Abstract

Context. Jeans escape is believed to dominate atmospheric escape for most outer Solar System bodies. However, non-thermal mechanisms, particularly atmospheric and ionospheric chemistry, are likely to contribute substantially to neutral escape on Triton. Aims. This study is devoted to evaluating the role of the chemically induced escape of H, H2, C, N, O, N2, and CO on Triton via a variety of processes. Here, we also aim to identify the dominant processes for these species. Methods. We used the background atmospheric and ionospheric structures from available model calculations. We constructed a test particle Monte Carlo model to determine the escape probability profiles of various species released from 35 channels. Species-dependent and energy-dependent cross sections were adopted in our calculations, along with a strongly forward-scattering angle distribution, all constrained by the available laboratory measurements. Results. The chemical escape rates on Triton are derived as 4.5 × 1024 s−1 for total H, 6.9 × 1022 s−1 for total C, 8.0 × 1024 s−1 for total N, and 1.4 × 1023 s−1 for total O. Conclusions. Based on a comparison with the respective Jeans escape rates, our calculations indicate that atmospheric and ionospheric chemistry make small but non-negligible contributions to both H and C escape on Triton, whereas its contributions to N and O escape are significant.