Science Priorities for the Extraction of the Solid MSR Samples from their Sample Tubes NASA-ESA Mars Rock Team

editorial reviewedPreservation of the chemical and structural integrity of samples that will be brought back from Mars is paramount to achieving the scientific objectives of MSR. Given our knowledge of the nature of the samples retrieved at Jezero by Perseverance, at least two options need to be tested for opening the sample tubes: (1) One or two radial cuts at the end of the tube to slide the sample out. (2) Two radial cuts at the ends of the tube and two longitudinal cuts to lift the upper half of the tube and access the sample. Strategy 1 will likely minimize contamination but incurs the risk of affecting the physical integrity of weakly consolidated samples. Strategy 2 will be optimal for preserving the physical integrity of the samples but increases the risk of contamination and mishandling of the sample as more manipulations and additional equipment will be needed. A flexible approach to opening the sample tubes is therefore required, and several options need to be available, depending on the nature of the rock samples returned. Both opening strategies 1 and 2 may need to be available when the samples are returned to handle different sample types (e.g., loosely bound sediments vs. indurated magmatic rocks). This question should be revisited after engineering tests are performed on analogue samples. The MSR sample tubes will have to be opened under stringent BSL4 conditions and this aspect needs to be integrated into the planning

Dissolution of apatite: Micro and Nanoscale insights

International audienceApatite is the most abundant phosphate mineral on Earth. In addition to being the foundation of the global phosphorus cycle, it is the most abundant mineral in the human body and is thought to have played a crucial role in the development of life. Despite its key role, little is known about its dissolution behavior at the atomic scale. Based on recent studies [1,2], there is strong evidence that dissolution of multi-cation silicate minerals are controlled by a coupled interfacial dissolution-reprecipitation (CIDR) process- we hypothesize that the same process controls phosphate mineral alteration.Determining what controls apatite weathering can impact many areas of environmental and medical mineralogy such as dentistry, contaminant scavenging, geochronology or paleoenvironment studies.To test our hypothesis, we acid-reacted crystals of fluorapatite (FAp) and hydroxylapatite (HAp) in flow- through devices with pH 2 HNO3 solutions. Determination of the mechanisms of dissolution was carried at multiple scales usingaqueouschemistry(macroscale),SEM-EDS (microscale) and STEM-HAADF-EELS on FIB liftouts (nanoscale).At the macroscale, we observed that the anionic composition of the apatite controls its weathering rate with, unsurprizingly, faster dissolution rates for HAp compared to FAp. SEM characterization of the crystal surface pre- and post-dissolution revealed the development of etch pits during dissolution, which were more pronouced for FAp than HAp. Observation of the mineral/solution interface at the nanoscale using STEM-HAADF revealed the development of a nanometric amorphous layer depleted in Ca compared to P.The observation of a sharp crystalline/amorphous transition of just a few nanometer, associated with sharp depletion in Ca, suggests that, similar to silicate, apatite is controlled by a CIDR mechanism. This discovery has the potential to transform our understanding of phosphate behavior in medical and environmental mineralogy.[1] Hellmann et al., 2012, Chem Geol, 294 [2] Daval et al., 2018, EPSL, 498Go