Preliminary Planning for Mars Sample Return (MSR) Curation Activities in a Sample Receiving Facility (SRF)

The Mars Sample Return Planning Group 2 (MSPG2) was tasked with identifying the steps that encompass all the curation activities that would happen within the MSR Sample Receiving Facility (SRF) and any anticipated curation-related requirements. An area of specific interest is the necessary analytical instrumentation. The SRF would be a Biosafety Level-4 facility where the returned MSR flight hardware would be opened, the sample tubes accessed, and the martian sample material extracted from the tubes. Characterization of the essential attributes of each sample would be required to provide enough information to prepare a sample catalog used in guiding the preparation of sample-related proposals by the world's research community and informing decisions by the sample allocation committee. The sample catalog would be populated with data and information generated during all phases of activity, including data derived concurrent with Mars 2020 sample-collecting rover activity, sample transport to Earth, and initial sample characterization within the SRF. We conclude that initial sample characterization can best be planned as a set of three sequential phases, which we have called Pre-Basic Characterization (Pre-BC), Basic Characterization (BC), and Preliminary Examination (PE), each of which requires a certain amount of instrumentation. Data on specific samples and subsamples obtained during sample safety assessments and time-sensitive scientific investigations would also be added to the catalog. There are several areas where future work would be beneficial to prepare for the receipt of samples, which would include the design of a sample tube isolation chamber and a strategy for opening the sample tubes and removing dust from the tube exteriors. All material collected from Mars (gases, dust, rock, regolith) would need to be carefully handled, stored, and analyzed following Earth return to minimize the alteration or contamination that could occur on Earth and maximize the scientific information that can be attained from the samples now and into the future. A Sample Receiving Facility (SRF) is where the Earth Entry System (EES) would be opened and the sample tubes opened and processed after they land on Earth. Samples should be accessible for research in biocontainment for time-sensitive studies and eventually, when deemed safe for release after sterilization or biohazard assessment, should be transferred out of biocontainment for allocation to scientific investigators in outside laboratories. There are two main mechanisms for allocation of samples outside the SRF: 1) Wait until the implementation of the Sample Safety Assessment Protocol (Planetary Protection) results concludes that the samples are non-hazardous, 2) Render splits of the samples non-hazardous by means of sterilization. To make these samples accessible, a series of observations and analytical measurements need to be completed to produce a sample catalog for the scientific community. Specialist members of the Mars Sample Return Planning Group Phase 2 (MSPG2), referred to here as the Curation Focus Group, have identified four curation goals that encompass all of the activities within the SRF: Documentation of the state of the sample tubes and their contents prior to opening, Inventory and tracking of the mass of each sample, Preliminary assessment of lithology and any macroscopic forms of heterogeneity (on all the samples, non-invasive, in pristine isolators), Sufficient characterization of the essential attributes of each sample to prepare a sample catalog and respond to requests by the sample allocation committee (partial samples, invasive, outside of pristine isolators). The sample catalog will provide data for the scientific community to make informed requests for samples for scientific investigations and for the approval of allocations of appropriate samples to satisfy these requests. The sample catalog would be populated with data and information generated during all phases of activity, including data derived from the landed Mars 2020 mission, during sample collection and transport to Earth, and reception within the Sample Receiving Facility. Data on specific samples and subsamples would also be generated during curation activities carried out within the Sample Receiving Facility and during sample safety assessments, time-sensitive studies, and a series of initial sample characterization steps we refer to as Pre-Basic Characterization (Pre-BC), Basic Characterization (BC), and Preliminary Examination (PE) phases. A significant portion of the Curation Focus Group's efforts was to determine which instrumentation would be required to produce a sample catalog for the scientific community and how and when certain instrumentation should be used. The goal is to provide enough information for the PIs to request material for their studies but to avoid facilitating studies that target scientific research that is better left to peer-reviewed competitive processes. We reviewed the proposed scientific objectives of the International MSR Objectives and Samples Team (iMOST) (Beaty et al., 2019) to make sure that the instrumentation suggested is sufficient to cover these key science planning questions (Table 1; Section S-6). It was determined that for Pre-Basic Characterization, two instruments are required, a Magnetometer (see Section S-1.1) and an X-ray Computed Tomography scanner (XCT see Section S-1.2). For Basic Characterization, there are four instruments that are considered necessary, which are analytical balance(s) (see Section S-2.1), binocular microscopes (see Section S-2.2), and multispectral imaging and hyperspectral scanning systems (see Section S-2.3). Then in Preliminary Examination, there is a set of instruments that should be available for generating more detailed information for the sample catalog. These are a Variable Pressure-Field Emission Scanning Electron Microscope (VP-FE-SEM see Section S-3.1), Confocal Raman spectrometer (see Section S-3.2), Deep UV Fluorescence (see Section S-3.3), a Fourier Transform Infrared Spectrometer (see Section S-3.4), a Micro X-ray Diffractometer (see Section S-3.5), X-ray Fluorescence Spectrometer (see Section S-3.6), and Petrographic and Stereo Microscope (see Section S-3.7). All instruments are summarized in Table 1. Finally, our Curation Focus Group has outlined several specific findings for sample curation within the SRF to complete the sample catalog prior to sample distribution and made several recommendations for future work (summarized in Section 8.1) to build upon the efforts that generated this report. MAJOR FINDING C-1: The initial sample characterization in the Sample Receiving Facility of the MSR samples can be broken down into three stages for simplicity as follows: Pre-Basic Characterization (Pre-BC), Basic Characterization (BC), and Preliminary Examination (PE). While the whole collection would be assessed through Pre-BC and BC, only subsets of samples would be used during the PE phase. FINDING C-2: Immediately after Earth landing, the spacecraft would be recovered and placed in a container designed to control and stabilize its physical conditions. The optimum temperature (Toptimum) of the sample tubes during transport to the Sample Receiving Facility (SRF) should be the same as the operating temperature of the SRF to avoid unnecessary temperature shock. FINDING C-3: The Sample Receiving Facility (SRF) should operate at room temperature (∼15-25°C), and the samples should be held at this temperature through all steps of initial sample characterization, with the option for cold storage of subsamples available in the SRF when needed. MAJOR FINDING C-4: Measurements on all the sample tubes before they are opened are essential to conduct as the samples could be compromised upon opening of the tubes. This step is called Pre-Basic Characterization (Pre-BC). These are measurements that would inform how the tubes are opened, processed, and subsampled during Basic Characterization (BC). MAJOR FINDING C-5: Careful collection and storage of the serendipitous dust on the outside of the sample tubes is a critical step in the curation process in the Sample Receiving Facility. The dust collected is a valuable resource to the scientific community. MAJOR FINDING C-6: Careful collection and storage of the unaltered and unfractionated headspace gas collected from the sample tubes is a critical step in the curation process in the Sample Receiving Facility. The gas collected is a valuable resource to the scientific community. FINDING C-7: To minimize the interaction of Earth atmospheric gases and gases that are in the sealed sample tubes, once the dust is removed from the exterior of the sample tubes, they should be placed into individual sample tube isolation chambers (STIC) as quickly as possible. FINDING C-8: There are compelling reasons to perform penetrative 3D imaging prior to opening the sample tubes. A laboratory-based X-ray Computed Tomography scanner is the best technique to use and the least damaging to organics of the penetrative imaging options considered. MAJOR FINDING C-9: Measurements on all the samples once the sample tubes are opened within the pristine isolators are essential to make initial macroscopic observations such as weighing, photographing, and optical observations. The first step to this stage is removal and collection of the headspace gas, which then starts the clock for time-sensitive measurements. This step is called Basic Characterization (BC). FINDING C-10: To avoid cross contamination between samples, it is recommended that, for processing through the isolators, the samples are organized into groups that have like properties. Given what we know about the geology of Jezero Crater, a reasonable starting assumption is five such groups. MAJOR FINDING C-11: Assuming that sample processing rates are reasonable and the samples are organized into five sets for cross contamination avoidance purposes, at least twelve pristine isolators are required to perform Basic Characterization on the MSR samples. This total would increase by two for each additional distinct processing environment. MAJOR FINDING C-12: More advanced measurements on subsamples, beyond those included in BC, are essential for the allocation of material to the scientific community for investigation, including some measurements that can make irreversible changes to the samples. These types of measurements take place during Preliminary Examination (PE). FINDING C-13: The output of the initial sample characterization, and a key function of the curation activities within the Sample Receiving Facility, is to produce a sample catalog that would provide relevant information on the samples' physical and mineralogical/chemical characteristics (derived from the Pre-Basic Characterization, Basic Characterization, and Preliminary Examination investigations), sample safety assessments, time-sensitive studies, and information derived from mission operations to enable allocation of the most appropriate materials to the scientific community. FINDING C-14: A staffing model for curation activities, including technical support and informatics/ documentation support, should be developed (as part of ongoing Sample Receiving Facility development) to ensure that the Sample Receiving Facility is staffed appropriately to support sample curation activities. FINDING C-15: To reduce the risk of catastrophic loss of samples curated in a single facility up to, and including, decadal timescales, the sample collection should be split-once it is possible to do so-and housed in more than one location for the purpose of maximizing the long-Term safety of the collection.