Browsing by Author "Siebach, Kirsten"

Now showing 1 - 6 of 6
  • Thumbnail Image
    Item
    The Chemistry and Mineralogy (CheMin) X-ray Diffractometer on the MSL Curiosity Rover: A Decade of Mineralogy from Gale Crater, Mars
    (MDPI, 2024) Blake, David; Tu, Valerie; Bristow, Thomas; Rampe, Elizabeth; Vaniman, David; Chipera, Steve; Sarrazin, Philippe; Morris, Richard; Morrison, Shaunna; Yen, Albert; Downs, Robert; Hazen, Robert; Treiman, Allan; Ming, Douglas; Downs, Gordon; Achilles, Cherie; Castle, Nicholas; Peretyazhko, Tanya; De Marais, David; Craig, Patricia; Lafuente, Barbara; Tutolo, Benjamin; Hausrath, Elisabeth; Simpson, Sarah; Walroth, Richard; Thorpe, Michael; Meusburger, Johannes; Pandey, Aditi; Gailhanou, Marc; Dera, Przemyslaw; Berger, Jeffrey; Thompson, Lucy; Gellert, Ralf; McAdam, Amy; O’Connell-Cooper, Catherine; Sutter, Brad; Morookian, John Michael; Fraeman, Abigail; Grotzinger, John; Siebach, Kirsten; Madsen, Soren; Vasavada, Ashwin; Earth, Environmental and Planetary Sciences
    For more than a decade, the CheMin X-ray diffraction instrument on the Mars Science Laboratory rover, Curiosity, has been returning definitive and quantitative mineralogical and mineral–chemistry data from ~3.5-billion-year-old (Ga) sediments in Gale crater, Mars. To date, 40 drilled rock samples and three scooped soil samples have been analyzed during the rover’s 30+ km transit. These samples document the mineralogy of over 800 m of flat-lying fluvial, lacustrine, and aeolian sedimentary rocks that comprise the lower strata of the central mound of Gale crater (Aeolis Mons, informally known as Mt. Sharp) and the surrounding plains (Aeolis Palus, informally known as the Bradbury Rise). The principal mineralogy of the sedimentary rocks is of basaltic composition, with evidence of post-depositional diagenetic overprinting. The rocks in many cases preserve much of their primary mineralogy and sedimentary features, suggesting that they were never strongly heated or deformed. Using aeolian soil composition as a proxy for the composition of the deposited and lithified sediment, it appears that, in many cases, the diagenetic changes observed are principally isochemical. Exceptions to this trend include secondary nodules, calcium sulfate veining, and rare Si-rich alteration halos. A surprising and yet poorly understood observation is that nearly all of the ~3.5 Ga sedimentary rocks analyzed to date contain 15–70 wt.% of X-ray amorphous material. Overall, this >800 m section of sedimentary rock explored in lower Mt. Sharp documents a perennial shallow lake environment grading upward into alternating lacustrine/fluvial and aeolian environments, many of which would have been habitable to microbial life.
  • Thumbnail Image
    Item
    Differences between modern and ancient Martian grain size distributions may reveal different paleoatmospheric conditions and provenance
    (Rice University, 2023) Preston, Sarah Lucille; Siebach, Kirsten
    Grain size distributions in eolian (wind-blown) deposits encode information about the atmospheric conditions that enabled their transport and deposition, and grain shape encodes information about provenance and postdepositional processes. Gale crater is a ~3.7 Ga impact crater with a vast diversity of exposed sedimentary strata indicative of a varied depositional history during the ear ly Hesperian epochs (Banham et al., 2018). The Stimson sandstone is a ~3 Ga unit of eolian sandstone in Gale crater that appears to have a coarser grain size distribution than the nearby Bagnold Dunes, an active dune field (Banham et al., 2018; Weitz et al., 2018). In this work, I hypothesize that the Martian paleoatmosphere had a different density than Mars’ current atmosphere, and that the source of the Stimson sandstone may have been more coarse than the source of the Bagnold dunes, leading to ancient sandstones with different grain size distributions than modern active sand dunes. To approach this question, I analyze images from the Mars Science Laboratory (MSL) Curiosity’s Mars Hand Lens Imager (MAHLI) and Remote Micro Imager cameras to determine the grain size distribution of targets. Additionally, I qualitatively describe grain shape and appearance, including roundedness, sphericity, pitting, and color, along with chemical composition where possible, to determine whether differences in grain size distributions can be attributed to provenance. From these results, I explore the role of paleoclimate and provenance in generating the grain size distribution seen in the Stimson. These results will help determine the provenance of the Stimson, as well as ancient Martian atmospheric conditions, in turn providing insights into the wet-to-dry transition and, potentially, the habitability of ancient Mars.
  • Thumbnail Image
    Item
    Final Report on Degradation of "Scholar's Way" for the Museum of Fine Arts, Houston
    (5/2/2023) Rajan, Bavan; Siebach, Kirsten
    The purpose of this project is to understand the chemical processes that contribute to the degradation of “Scholar’s Way,” a trio of heavily altered basalt sculptures at the Museum of Fine Arts, Houston (MFAH). They were installed at the MFAH in 2020 after their creation in 2018 by South Korean artist Byung Hoon Choi. The work sits in a shallow pond in the museum’s sculpture garden, exposed to Houston’s warm humid climate and regular HCl from treatments to prevent algae growth. After less than 3 years, fragments of the sculptures have been lost, the surfaces have altered in coloration, and salt-like minerals regularly precipitate on the sides of the sculptures. The mineralogy of the sculptures and associated precipitates can inform the MFAH of how and why “Scholar’s Way”, as well as other outdoor sculptures, might be degrading, as well as what steps they can take to preserve their artwork. Visual and Near Infrared Spectroscopy, speciation modeling from the pond’s water chemistry, Electron Dispersive X-ray spectroscopy, and Electron Probe Microanalysis were used to determine 1) the chemical composition of the water features and sculptures, which reveal plausible degradation mechanisms, 2) potential ongoing mineral dissolution, and 3) the drivers of salt precipitation from the pond. These results, along with recommendations to preserve the work, have since been presented to the MFAH in the attached executive summary and technical report.
  • Thumbnail Image
    Item
    The Fate of Nitrogen in Highly Reducing Magmatic Systems: Implications for the Parent Body Partial Melting and Magma Ocean Crystallization in the Inner Solar System
    (2021-01-22) Falksen, Emily; Dasgupta, Rajdeep; Siebach, Kirsten
    Evolution of nitrogen (N), a life-essential volatile element, in highly reduced magmatic systems is key for the origin of N on terrestrial planets formed via accretion of reduced chondritic parent body materials, planetesimals, and embryos, which themselves underwent partial or complete differentiation. To investigate the stability of N-bearing minerals in partially molten silicate-rich systems as well as solubility of nitrogen in silicate melts and silicate minerals, we performed laboratory experiments at pressures (P) of 1.5-3.0 GPa and temperatures (T) of 1300-1600 °C in a graphite capsule with oxygen fugacity conditions ranging from IW – 5.87 to IW – 8.35. All experiments yielded silicate melt + nierite (Si3N4) + Fe-rich alloy melt + N-rich vapor ± sinoite ± cpx. Sinoite was restricted to above 1400-1500 °C, while cpx was restricted to below these temperatures. Solubility of nitrogen and Nitrogen Concentration at Silicon-Nitride Saturation (NCNS) increases with increasing pressure and temperature and ranges between 3.57 and 9.46 wt %. Using high pressure N solubility data from this study and similar solubility data for silicate melts at ambient and low pressures, we derive the following N solubility model N(ppm)=〖P_(N_2)^0.5*exp〗⁡(8.12(±1.56)+(1000*(-12.23(±2.81)-0.61(±0.29) P_total^0.5 ))/T-1.45(±0.06)(∆IW)) +P_(N_2 )*exp⁡(7.96(±0.48)-18.59(±7.17) X_MgO+2.57(±0.94)(NBO/T)) where T is temperature in K, P_(N_2 ) is partial pressure of N2 in GPa, P_(total ) is the equilibrium pressure in GPa, IW is the log oxygen fugacity relative to the IW (oxygen fugacity imposed by coexistence of Iron, Fe, and iron oxide, wüstite) buffer, XMgO is the mole fraction of MgO in the silicate melt, and NBO/T is total non-bridging oxygen relative to tetrahedral cations (NBO/T = (2 × Total O)/T – 4, where T = Si + Ti + Al + Cr + P (e.g. (Mysen et al., 1982)). Solubility of nitrogen in cpx was measured to between 1.51 and 2.05 wt% and resulted in cpx/silicate melt partition coefficients for nitrogen of ~0.4 to ~0.2. These cpx/silicate melt nitrogen partition coefficients (DNcpx-melt) are much larger than that previously estimated at more oxidizing conditions, suggesting N maybe less incompatible during thermal processing of rocky reservoirs at extremely reducing conditions. Similar to previous studies, N also shows lithophile behavior at extremely reduced, graphite saturated conditions, with partition coefficient of N between Fe-rich alloy melt and silicate melt to be between 0.2 and 0.7 at our experimental conditions. While partition coefficient of N between cpx and Fe-rich alloy melt was found to be between 1.6 and 2.1, but there lacks enough data to determine a dependence with P-T-fO2. The application of our N solubility data and model suggests that mobilization of N from the deeper, partially molten reservoir to shallower reservoirs is possible in reduced planetesimals and internally differentiated meteorite parent bodies. Similarly, enrichment of N in the planetary atmosphere may be a result of gradually more oxidizing accreting materials, which would lead to N being more and more incompatible during internal and external magma ocean processing of rocky bodies.
  • Thumbnail Image
    Item
    Vikings, Volcanoes, and Satellites: An Analysis of Icelandic NDVI Trends and the Problem of Scale in Vegetation Remote Sensing
    (Rice University, 2024-05) Wilcox, Marlo C.; Siebach, Kirsten
    The devil is in the details, especially for remote sensing where the scale of the imagery does not always match the scale of interpretation. Iceland, a subarctic volcanic island in the north Atlantic, has a long history of dynamic vegetation changes. However, the scale at which these changes occur may be smaller than the resolution of datasets most commonly used to study arctic vegetation trends. In this study, I used MODIS Aqua 250m satellite imagery to evaluate nationwide trends in Normalized Difference Vegetation Index (NDVI) over the past twenty years. Then, for a handful of sites r epresenting land cover classifications of interest, I used 30-meter Harmonized Landsat and Sentinel-2 (HLS) imagery to quantify information loss between the 30m trend map and several synthetically upscaled trend maps. Over Iceland as a whole, the trend in NDVI was found to be minimal. However, the higher resolution imagery revealed dynamic trends which are lost at lower resolutions. The greatest information loss occurred in highly heterogeneous land cover classes, with a maximum information loss of 63% from 30m to 240m and 90% from 30m to 1000m. Additionally, I found that the way in which land cover classifications are defined has the potential to impact interpretation. Neither of these complexities have been addressed in previous studies of Icelandic vegetation trends and have rarely been addressed in studies of Arctic vegetation trends as a whole. My findings support the need for greater consideration of ecosystem classification and scale dependencies in any work aimed at using sa tellite remote sensing to better understand Arctic greening.
  • Thumbnail Image
    Item
    When is Drone Photogrammetry Useful for Flood Risk Assessment?
    (Rice University, 2021-05) Sheldon, Jessica; Siebach, Kirsten
    Drone technology and the high resolution datasets it enables stand to revolutionize our understanding of the Earth’s surface. This research is Houston specific, and studies how drones can be used to systematically collect photogrammic data to detect environmental changes, and how that data is valuable for flood planning purposes. This data is the culmination of three years of research. Prior to this year, the focus has been learning to fly the drone, learning the image processing Pix4D and ArcMap 10.5, and creating a workflow for accurate image collection processing. This study has collected three separate datasets of the study area at Buffalo Bayou using a DJI Phantom 4 Pro drone. This data was then processed and modeled in Pix4D to create digital elevation models (DEMs). The DEMs were calibrated and analyzed in GIS, and compared to the publicly available 2018 LIDAR data. Our research catalogs high resolution change over time of our study area, and documents the process of how drones can be used to systematically observe change over time. Additionally, our data highlights the difference in resolution between a low elevation drone flight versus a higher elevation LIDAR scan.