[M-IS17] Aqua planetology

[MIS17-P06] Spectroscopic characterization of major interlayer cations in smectite

*Yohei Noji¹, Keisuke Fukushi² (1.Course in Earth and Planetary Science, School of Geoscience and CiviI Engineering College of Science and Engine ering, Kanazawa University, 2.Institute of Nature & Environmental Technology, Kanazawa University)

Keywords:Perseverance, Smectite, Infrared spectroscopy

Present Mars is a cold, dry planet, but it has been shown that liquid water once existed on its surface (Ojha et al., 2015). It has also been suggested that a large portion of past ocean water may still be present in the subsurface as frozen soil and hydrous minerals (Vaniman et al., 2013). The presence of hydrous minerals is considered important not only as an indicator of water, but also as a record of the water chemistry of the oceans and lakes that existed on the planet, as it provides clues to the water chemistry of the pore water that the hydrous minerals once came into contact with (Fukushi et al., 2019). The Perseverance rover of NASA's Mars 2020 mission is exploring Jezero crater, a former lake on Mars. In the Jezero crater, smectite, a hydrous mineral, is present in lake sediments (Ehlmann et al., 2008). Smectite has the property of exchanging interlayer cations with cations in solution. Therefore, it is possible to constrain the water chemistry of the pore water that was once in contact with the smectite by using the interlayer cation composition of the smectite (Fukushi et al., 2019). The purpose of this study is to develop a method to estimate the interlayer cation composition of smectite in the Jezero crater from the measured data on smectite in Persivereance. The Perseverance is also equipped with a device for Raman and Visible-Near-Infrared spectroscopy to perform detailed analysis on hydrous minerals. Raman and infrared spectroscopic measurements of laboratory-created smectite with a known fraction of interlayer cation species will be performed, and the increase or decrease of the peak area and the shift of the peak position will be analyzed. Then, we will discuss whether the interlayer cation composition of Martian smectite can be determined from the results of Raman and infrared spectroscopic measurements of smectite made by Perseverance on Mars.