Laboratory Studies of Cryogenic Outer Solar System Geologic Materials*

The Physics and Astronomy Department at Northern Arizona University hosts one of only a handful of laboratories around the world devoted to studies of astrophysical ices. Simple molecules like CH₄, N₂, CO, CO₂, O₂, CH₃OH, C₂H₆, and NH₃ are important geological materials in the cold outer regions of the solar system. Their mobility and distinct material properties enable geological activity and produce a spectacular variety of exotic landforms, even at extremely low temperatures. But frustratingly little is known of the basic mechanical and optical properties of these volatile ices, and especially of their mixtures.

In our lab setup, volatile ices are condensed within a 2 cm enclosed cell. We can cool down to 30 K in the closed cell, and 6 K on the thin film. Cryogenic ice samples are studied via various analytical techniques including visible and infrared transmission spectroscopy, photography, and Raman spectroscopy. Mass spectrometers are capable of monitoring changes in composition.

Some exciting results include applications to New Horizons’ infrared observations of Pluto, understanding the seas of Titan, and studying the surface of Europa. The ices that are created in the lab are useful to a variety of outer solar system bodies.

We would like to understand an array of physical properties as well, including density, viscosity, sound speed, vapor pressure, refractive index, compressibility, thermal and electrical conductivity, and diffusion rates. Our group includes expertise in physical chemistry, specifically using theoretical and computational chemistry to understand the behavior of complex condensed phase systems.  We are always looking for new students, and are eager to collaborate with other complementary facilities, as well as scientists who have a need for laboratory data to help with understanding mission and/or telescope data.