Thermal Chemistry of Ammonia Ice

Thermally-driven chemical reactions occur readily in a variety of astrophysical and planetary ice compositions despite the low temperatures and minimal diffusion characteristic of these environments. For example, several studies have demonstrated that inorganic sulfur compounds, including SO₂ and H₂S, react with H₂O and the strong, radiolytically produced oxidants O₃ and H₂O₂ at temperatures relevant to the outer Solar System ices (Moore et al. 2007; Loeffler and Hudson 2013, 2016; Kanuchová et al. 2017; Tribbett and Loeffler 2021). These sulfur compounds react to produce sulfur anions and hydrated states of sulfuric acid, and may contribute to the overall sulfur cycle of the icy satellite Europa. This example highlights the importance of considering potential thermally-driven reactions in astrochemical systems. In addition to the sulfur species prevalent on the Galilean satellites, ammonia species have been tentatively detected on several icy bodies including Charon and Miranda (Brown and Calvin 2000; Bauer et al. 2002). Here, we present spectral data demonstrating thermal reactivity within a H₂O + NH₃ + O₃ ice mixture at temperatures relevant to the outer Solar System. Our results will inform future studies observing H₂O and NH₃ rich ices.

Moore, M. H. et al., Icarus, 2007.

Loeffler and Hudson, Icarus, 2013.

Loeffler and Hudson, ApJL, 2016.

Kanuchová, Z. et al., Astron. Astrophys., 2017.

Tribbett and Loeffler, DPS Meeting 2021, 2021.

Brown and Calvin, Science, 2000.

Bauer, J. M. et al., Icarus, 2002.