"
 
行星科学研究中心
 Home  People  Data & PDS Service  Teaching Courses  Laboratories & Facilities  Press Center  About Us  中文 
 
About Us
 
  Academic progress
Position: English1 > About Us > Academic progress > Content
 
Thermal stability of akaganeite and its desiccation process under conditions relevant to Mars
2019-10-11 13:52:08 Xiaohui Fu    (點擊次數:)

Akaganeite has been found in Yellowknife Bay mudstones of the Gale crater by the Chemistry and Mineralogy X-ray diffraction instrument (CheMin) aboard the Curiosity rover. This phase has also been discovered in limited locations on Mars by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) aboard the Mars Reconnaissance Orbiter. Akaganeite has also been proposed as a precursor candidate of hematite on Mars. To better constrain the stability and occurrence of akaganeite on Martian surfaces, structural and spectral modifications of akaganeite introduced by heating and desiccation were systematically investigated. We found that the phase transformation from akaganeite to hematite starts at 245?°C, which is accompanied by the removal of chloride in tunnels. We propose that geological activities (e.g., impact and volcanism on Mars) could heat the surrounding area and cause the transformation of akaganeite into hematite in Martian rocks and surface materials. Relative humidity (RH) variations result in water combination and overtone absorptions band strength changes. The CRISM spectrum of akaganeite detected in the Robert Sharp crater shows relatively weak 1.39?μm band compared to that of desiccated akaganeite under simulated Martian environments, indicating that akaganeite found on Mars could be highly desiccated. The water adsorption of akaganeite occurred when exposed to ambient laboratory conditions (RH ~65%). This suggests the water adsorption and desorption of akaganeite on Mars correspond to RH changes in a diurnal cycle.


Figure 1 SEM image of unheated and thermal-treated akageneite

Figure 2 Comparison of laboratory hematite spectra to Pancam spectra of hematite spherules on Mars

Figure 3 CRISM spectrum of akaganeite at Robert Sharp crater plotted together with continuum removed NIR reflectance

spectra for akaganeite


https://doi.org/10.1016/j.icarus.2019.113435



關閉窗口