Reliable spectroscopic identification of minerals associated with serpentinization: Relevance to Mars exploration

Abstract

<p>Mars has become the preeminent target of <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/exobiology" title="Learn more about astrobiology from ScienceDirect's AI-generated Topic Pages">astrobiology</a> due to its many Earth-like features. Serpentinized environments on Mars are increasingly of astrobiological interest because they imply the presence of several of the “key elements” for life. The Mars 2020 rover carries a compelling set of spectral instruments with the intent to characterize past habitable serpentinized environments, search for potential biosignatures, and collect samples for potential return to Earth. Reliable spectroscopic identification of <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/serpentinization" title="Learn more about serpentinization from ScienceDirect's AI-generated Topic Pages">serpentinization</a> minerals is, of course, a prerequisite for mission accomplishment. The current assignment of spectroscopic features is based on the databases derived from pure minerals. However, many studies have confirmed that mineral assemblage can complicate spectrum identification, often leading to misinterpretation of the data. Therefore, a rock-based library should be built, which will increase our capability to interpret the Martian spectroscopic data. As such, we performed a comprehensive mineralogical and spectroscopic survey of several rocks sampled from an <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/ophiolite" title="Learn more about ophiolite from ScienceDirect's AI-generated Topic Pages">ophiolite</a> complex in Qaidam Basin, one of the largest Mars analogs on Earth, to build an <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/ophiolite" title="Learn more about ophiolite from ScienceDirect's AI-generated Topic Pages">ophiolite</a> spectral database. X-ray fluorescence (XRF), visible and near-infrared (VNIR), <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/raman-spectroscopy" title="Learn more about Raman spectroscopy from ScienceDirect's AI-generated Topic Pages">Raman spectroscopy</a>, and XRD were used to identify minerals in the rocks. The results show that serpentine in the rocks with talc could be misinterpreted as <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/sepiolite" title="Learn more about sepiolite from ScienceDirect's AI-generated Topic Pages">sepiolite</a> only relying on the Raman vibrations, while the VNIR spectra can identify serpentine well in all rocks. In addition, the camera and Raman spectrometer on the Mars rover should work together to identify different polymorphs of serpentine, i.e., <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/antigorite" title="Learn more about antigorite from ScienceDirect's AI-generated Topic Pages">antigorite</a>, <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/lizardite" title="Learn more about lizardite from ScienceDirect's AI-generated Topic Pages">lizardite</a>, and chrysotile. Raman and/or VNIR spectroscopy is effective for other minerals associated with <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/serpentinization" title="Learn more about serpentinization from ScienceDirect's AI-generated Topic Pages">serpentinization</a>, including <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/brucite" title="Learn more about brucite from ScienceDirect's AI-generated Topic Pages">brucite</a>, dolomite, magnesite, magnetite, talc, and quartz. Our study provides a framework for detecting serpentinization minerals on Mars with spectrometers and can be used for data interpretation by the Mars 2020 mission. All the spectral data presented in the supplementary material facilitate further comparison with future in situ and orbital measurements on Mars.<br></p>