Jennifer Hanley

Near‐ and mid‐infrared reflectance spectra of hydrated oxychlorine salts with implications for Mars

The presence and distribution of oxychlorine salts (e.g., chlorates and perchlorates) on Mars have implications for the stability of water, most notably, that they lower the freezing temperature. To date, elemental chlorine has been measured by all lander missions, with the perchlorate ion identified at both the Phoenix and Curiosity landing sites, but detection by near-infrared (NIR) and mid-infrared (MIR) remote sensing has been limited to deposits of anhydrous chlorides. Given that oxychlorine salts can form numerous hydrated phases, we have measured their NIR and MIR reflectance spectra from 1 to 25u2009µm for comparison to data collected from orbiting spectrometers. Anhydrous oxychlorine salts show almost no features in the NIR, except for small bands of residual adsorbed water. However, hydrated oxychlorine salts show numerous features due to water in the NIR, specifically at ~1.4 and ~1.9u2009µm. Increasing the hydration state increases the depth and width of the water bands. All oxychlorine salts exhibit an additional feature at ~2.2u2009µm due to a Cl-O combination or overtone feature, although it is less prominent in the hydrated perchlorate salts, likely overwhelmed by the ClO4-H2O feature at 2.14u2009µm. All oxychlorine salts show features in the MIR due to the fundamental vibrations of Cl-O longward of ~8u2009µm. The NIR spectral features of hydrated oxychlorine salts are similar to other hydrated salts, especially hydrated sulfates; thus, identification from orbit may be ambiguous. However by utilizing the NIR and MIR laboratory data presented here for comparison, oxychlorine salts may be detectable by orbiting spectrometers.

Near‐infrared spectroscopy of lacustrine sediments in the Great Salt Lake Desert: An analog study for Martian paleolake basins

The identification and characterization of aqueous minerals within ancient lacustrine environments on Mars are a high priority for determining the past habitability of the red planet. Terrestrial analog studies are useful both for understanding the mineralogy of lacustrine sediments, how the mineralogy varies with location in a lacustrine environment, and for validating the use of certain techniques such as visible–near-infrared (VNIR) spectroscopy. In this study, sediments from the Pilot Valley paleolake basin of the Great Salt Lake desert were characterized using VNIR as an analog for Martian paleolake basins. The spectra and subsequent interpretations were then compared to mineralogical characterization by ground truth methods, including X-ray diffraction, automated scanning electron microscopy, and several geochemical analysis techniques. In general, there is good agreement between VNIR and ground truth methods on the major classes of minerals present in the lake sediments and VNIR spectra can also easily discriminate between clay-dominated and salt-dominated lacustrine terrains within the paleolake basin. However, detection of more detailed mineralogy is difficult with VNIR spectra alone as some minerals can dominate the spectra even at very low abundances. At this site, the VNIR spectra are dominated by absorption bands that are most consistent with gypsum and smectites, though the ground truth methods reveal more diverse mineral assemblages that include a variety of sulfates, primary and secondary phyllosilicates, carbonates, and chlorides. This study provides insight into the limitations regarding the use of VNIR in characterizing complex mineral assemblages inherent in lacustrine settings.

LABORATORY STUDIES OF CRYOGENIC OUTER SOLAR SYSTEM MATERIALS

Introduction: The Physics and Astronomy Department at NAU hosts the Astrophysical Ice Laboratory, which is dedicated to studying ices under controlled temperatures and pressures [1-5]. Simple molecules like CH4, H2O, 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. Many outer Solar System bodies exhibit interesting phenomena that indicates active processes on geologically recent timescales. For instance, New Horizons imaged what appears to be flows of nitrogen ice on Pluto (Figure 1 top), possibly created through convective cells of buoyant nitrogen ice. How does nitrogen ice behave at these temperatures and pressures?

Reflectance spectra of hydrated chlorine salts: The effect of temperature with implications for Europa: NIR Spectra of Low Temp Chlorine Salts

Hydrated chlorine salts are expected to exist on a variety of planetary bodies, including inner planets such as Mars and outer planet satellites such as Europa. However, detection by remote sensing has been limited due to a lack of comparison data in spectral libraries. In addition, at low temperatures spectral features of many H2O-bearing species deviate from their room temperature behavior. Thus, we acquired spectra of NaCl, NaClO4·nH2O, MgCl2·nH2O, Mg(ClO4)2·6H2O, and Mg(ClO3)2·6H2O from 0.35 to 2.5u2009µm at both 298 and 80u2009K to observe the effects of temperature on diagnostic spectral features. In the near-infrared, the strongest spectral features often arise from water molecules. Increasing hydration states increases the depth and width of water bands. Interestingly, at low temperature these bands become narrower with sharper, better defined minima, allowing individual bands to be more easily resolved. We also measured frozen eutectic solutions of NaCl, MgCl2, and KCl. We show that while care must be taken to acquire laboratory spectra of all hydrated phases at the relevant conditions (e.g., temperature and pressure) for the planetary body being studied, chlorine salts do possess distinct spectral features that should allow for their detection by remote sensing.