DIX Planetary Science Seminar

Radiation alters the structure and chemistry of icy planetary surfaces through processes that include sputtering, radiolysis, and amorphization. Decades of literature demonstrate that these radiation-driven processes can be studied using thin film ice analogs, and the results enable the interpretation of icy planetary environments throughout the Solar System. Conversely, the thermally-driven alteration of icy materials receives significantly less attention in the literature due to the cold temperatures characteristic of the outer Solar System, and the limited mobility associated with solid-state material. Recent laboratory studies demonstrate that despite the low temperatures, thermal reactions occur readily within specific chemical systems that include common astrophysical molecules (Noble et al. 2012; Loeffler and Hudson 2013, 2015, 2016). In some cases, these reactions occur on laboratory time scales at temperatures as low as 70 K. These studies suggest that astrochemical modeling efforts and observational surveys may need to consider thermally-driven chemistry to derive a comprehensive understanding of icy planetary surfaces.

Here, I present two chemical systems with astrophysically-relevant compositions that demonstrate thermally-driven chemistry at low temperatures. All experiments were performed within an ultrahigh vacuum chamber that I constructed in the Processes, Environments and Astrochemistry on Extraterrestrial Surfaces (PEAXS) Laboratory at Northern Arizona University. All ice samples and their thermal products were characterized in situ using a combination of analytical tools that includes infrared spectroscopy, mass spectrometry, and microbalance gravimetry. The reaction products in both cases are consistent with astronomical observations of outer Solar System materials and may play an important role in the interpretation of future compositional studies.