title: Bright and Dusty Regions of Mars: New Insights from Experiments and Orbital Color Imaging
Creators: name: Valantinas, Adomas
Publisher: name: Universität Bern
Year: 2024
Subjects: subject: 520 Astronomy
subject: 530 Physics
subject: 620 Engineering

description: This PhD thesis contributes to the investigation of the origin of Mars dust and analyzes dynamic processes in Mars bright, dusty regions. To understand the nature of the active phenomena and the spectral characteristics of Martian dust this work employs a combination of orbital observations and laboratory bi-directional reflectance measurements of ferric iron oxide powders. Orbital observations are mostly derived from the Colour and Stereo Surface Imaging System (CaSSIS; Thomas et al., 2017) on board the ESA’s ExoMars Trace Gas Orbiter (TGO), which present novel multispectral data that is exploited here for high precision photometry. The orbital observations are complemented by laboratory measurements using the PHysikalisches Institut Radiometric Experiment-2 (PHIRE-2; Pommerol et al., 2011) and the Mobile Hyperspectral Imaging System (MoHIS; Pommerol et al., 2015) at the University of Bern. The use of the CaSSIS orbital data is at the core of each chapter of this thesis. 
Chapter 2 analyzes the observations of active geomorphologic features known as slope streaks in the dusty regions of Mars. Substantial differences in their surface structures were determined using CaSSIS multi-angular observations. To study the particle size effects on the reflectance of slope streaks we employed PHIRE-2 measurements of sieved size fractions of Mars Global Simulant (MGS-1; Cannon et al., 2019) and the Hapke (2012) reflectance model. It was determined that a decrease in brightness can be caused by a decrease in particle size. This chapter was published in the Planetary and Space Science journal (Valantinas et al., 2021). 
Chapter 3 presents the discovery of tropical frost on Martian volcanoes, which is significant because frost was not observed in these latitudes before. These observations of dusty, high altitude and low thermal inertia areas provide a deeper understanding of the current Mars climate. The high signal-to-noise ratio (SNR) and the capability of CaSSIS to image any given point at various local times allows sharp imaging of processes never observed before. We intend to submit this chapter to Geophysical Research Letters. 
Chapter 4 focuses on preliminary analyses of the photometry of Mars bright and dusty regions. The comparison of CaSSIS color data and laboratory PHIRE-2 measurements of various iron oxide powders revealed that ferrihydrite is the dominant mineral phase present in Martian dust. This finding indicates cold and icy conditions on Mars and limited liquid water activity in the latest geologic epoch. Additionally, using CaSSIS multi-angular data, phase curves for Martian dust deposits are derived. We intend to submit this work to a high-impact journal. 
Appendix A presents additional work published in the journal Geology. It was partly conducted at the University Bern but is not directly related to the PhD thesis topic. Valantinas & Schultz (2020) report the discovery of an active tectonic system of wrinkle ridges on the nearside of the Moon. This finding is important because for decades the Moon was considered a geologically “dead” body. Lithospheric stresses under the active wrinkle ridge systems may be sources of deep moonquakes, which might be detected by future geophysical missions foreseen by NASA (Haviland et al., 2022). 
Appendix B includes additional results that are not shown in Chapter 4. This comprises phase curves and phase curve color ratios of selected ferric iron oxides.
 This PhD thesis contributes to the investigation of the origin of Mars dust and analyzes dynamic processes in Mars bright, dusty regions. To understand the nature of the active phenomena and the spectral characteristics of Martian dust this work employs a combination of orbital observations and laboratory bi-directional reflectance measurements of ferric iron oxide powders. Orbital observations are mostly derived from the Colour and Stereo Surface Imaging System (CaSSIS; Thomas et al., 2017) on board the ESA’s ExoMars Trace Gas Orbiter (TGO), which present novel multispectral data that is exploited here for high precision photometry. The orbital observations are complemented by laboratory measurements using the PHysikalisches Institut Radiometric Experiment-2 (PHIRE-2; Pommerol et al., 2011) and the Mobile Hyperspectral Imaging System (MoHIS; Pommerol et al., 2015) at the University of Bern. The use of the CaSSIS orbital data is at the core of each chapter of this thesis. 
Chapter 2 analyzes the observations of active geomorphologic features known as slope streaks in the dusty regions of Mars. Substantial differences in their surface structures were determined using CaSSIS multi-angular observations. To study the particle size effects on the reflectance of slope streaks we employed PHIRE-2 measurements of sieved size fractions of Mars Global Simulant (MGS-1; Cannon et al., 2019) and the Hapke (2012) reflectance model. It was determined that a decrease in brightness can be caused by a decrease in particle size. This chapter was published in the Planetary and Space Science journal (Valantinas et al., 2021). 
Chapter 3 presents the discovery of tropical frost on Martian volcanoes, which is significant because frost was not observed in these latitudes before. These observations of dusty, high altitude and low thermal inertia areas provide a deeper understanding of the current Mars climate. The high signal-to-noise ratio (SNR) and the capability of CaSSIS to image any given 
point at various local times allows sharp imaging of processes never observed before. We intend to submit this chapter to Geophysical Research Letters. 
Chapter 4 focuses on preliminary analyses of the photometry of Mars bright and dusty regions. The comparison of CaSSIS color data and laboratory PHIRE-2 measurements of various iron oxide powders revealed that ferrihydrite is the dominant mineral phase present in Martian dust. This finding indicates cold and icy conditions on Mars and limited liquid water activity in the latest geologic epoch. Additionally, using CaSSIS multi-angular data, phase curves for Martian dust deposits are derived. We intend to submit this work to a high-impact journal. 
Appendix A presents additional work published in the journal Geology. It was partly conducted at the University Bern but is not directly related to the PhD thesis topic. Valantinas & Schultz (2020) report the discovery of an active tectonic system of wrinkle ridges on the nearside of the Moon. This finding is important because for decades the Moon was considered a geologically “dead” body. Lithospheric stresses under the active wrinkle ridge systems may be sources of deep moonquakes, which might be detected by future geophysical missions foreseen by NASA (Haviland et al., 2022). 
Appendix B includes additional results that are not shown in Chapter 4. This comprises phase curves and phase curve color ratios of selected ferric iron oxides.