| Planetary science is a multidisciplinary science, using physics, chemistry, geology etc., to study the properties of planets, satellites, and planet systems, especially the objects in our solar systems. Its history can begin from the Greek philosopher Democritus. Much progress has been made in the planetary science field after the appearance of telescope in the 17th century, as many planets were found in the solar system. Thanks to the new technology, people have started the space explorations from the middle of last century, which includes the missions to the Moon, Mars, Titan, Venus, Mercury, and Pluto etc. These missions have served us more detailed knowledge about the planets surrounding us than those from earth based telescopes. In the recent decades, many countries including China have shown their passion on the space exploration of moon, mars, and other planets. As belong to the fundamental planetary sciences, this work studies the lunar returned samples and the minerals relevant to Mars. The first project is the spectroscopic study of copiapite group minerals, which might be one important mineral group on Mars surface. The second project is the phase boundary study of hydrated ferric sulfates, which were already observed on the Martian surface. The third project is the study of the Ti distributions in two Apollo returned lunar samples.The identification of iron sulfates on Mars by the Mars Exploration Rovers and the Mars Reconnaissance Orbiter emphasized the importance of studying iron sulfates under in laboratory simulation experiments. The copiapite group mineral was suggested as one of the potential iron sulfates occurring at the surface and subsurface on Mars, so it is meaningful to study their spectroscopic features, especially the spectral changes caused by cation substitutions. Four copiapite samples with cation substitutions (Fe3+, Al3+, Fe2+, Mg2+) were synthesized in our laboratory. Their identities were confirmed by powder XRD. Spectroscopic characterizations by Raman, mid-IR, VIS-NIR, and laser-induced-breakdown spectroscopy (LIBS) were conducted on those synthetic copiapite samples, as these technologies are being (and will be) used in current (and future) missions to Mars. We have found a systematic v1 peak shift in Raman spectra of the copiapite samples with cation substitutions, a consistent atomic ratio detection by LIBS, a set of systematic XRD line shifts representing structural change caused by the cation substitutions and a violation of section rules in mid-IR spectra caused by the low site symmetry of [SO4]2- in copiapite structures. The NIR spectra of the trivalent copiapite species show two strong diagnostic water features near 1.4?m and 1.9?m with two additional bands near 2.0?m. In the Vis-NIR spectra, the position of an electronic band shifts from 0.85?m for ferricopiapite to 0.866?m for copiapite, and this shift suggests the appearance of a Fe2+ electronic transition band near 0.9?m.Recent findings of various ferric sulfates on Mars emphasize the importance of investigating the fundamental properties (stability field, phase boundary, phase transition pathway and reaction rates) of ferric sulfates at temperatures relevant to that of Martian surface. In this study, the phase boundary between kornelite (Fe2(SO4)3·7H2O) and pentahydrated ferric sulfate (Fe2(SO4)3·5H2O) was experimentally determined using the humidity-buffer technique together with gravimetric measurement and Raman spectroscopy at 0.1 MPa in the 36-56?temperature range. Through the thermodynamic analysis of our experimental data, the enthalpy change (-290.8±0.3 kJ/mol) and the Gibbs free energy change (-238.81±0.02kJ/mol) for each water molecule of crystallization in the rehydration of pentahydrated ferric sulfate to kornelite were obtained, and these data are consistent with other estimation.The ultraviolet-visible (UV-Vis) ratio is a widely used parameter to estimate the Ti distribution on the lunar surface, and new observations with the LRO wide-angle camera (WAC) are contributing to this effort with global measurements including bands at 321 and 360 nm. To better understand the correlation between UV-Vis ratio and Ti content, we have been doing laboratory analyses of lunar soil samples using a combined digital imaging (backscattered electron image and X-ray maps) method to get quantitative results on abundances. In this study, we report on the Ti distribution in two Ti-rich soils,10084 from Apollo 11 and 71501 from Apollo 17. The TiO2 concentration of bulk soil 10084 (Is/FeO=78) is 7.3 wt%, and that of bulk soil 71501 (Is/FeO=35) is 9.5 wt%. The dominant Fe-Ti oxide mineral in 10084 and 71501 is ilmenite; other Ti-rich oxides (armalcolite, ulvospinel, and rutile) are very scarce. In both soils, the volume percent of agglutinates and breccias decreases as grain-size fractions decrease, and the volume percentages of single mineral grains have a consistent trend to increase as grain-size fractions decrease. This trend results from breakdown of breccias and basalt lithic fragments into finer, single mineral grains. In mature soil 10084, more Ti is hosted in basalt as fine-grained ilmenite compared to the coarse, free ilmenite grains. In submature soil 71501, Ti is hosted mostly by coarse-grained ilmenite. This difference likely reflects initial basalt (ilmenite) characteristics. No unique trend was found on the Ti content distribution variation among these grain-size fractions, whereas the ilmenite shape in mature soil 10084 shows a subtle trend.The spectroscopic signatures of the copiapite group minerals may help us to distinguish these minerals on Mars by comparing the spectra we obtained in the lab with those from the spectrometers onboard Mars orbiters or Mars landers. The variation among the spectra of copiapite group minerals may further help us to determine different end-members of copiapite group minerals on Mars. Our study of the phase boundary between the two ferric sulfates served a methodology for further investigation of the phase boundaries between other pairs of hydrated ferric sulfates. The thermodynamic data derived and the phase boundary will help us to understand the appearance, the evolution and the distribution of ferric sulfates on Mars. Our third projects will serve data for the further study to correlate the intensity of UV-Vis spectra with the Ti distribution, the Ti hosts, and the ilmenite shapes of the lunar soils. |
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