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Andrew Steele

Publications and source records attributed to Andrew Steele.

7 recordsLinked to original sources
USGS2025

The abiotic background as a central component of a Sample Safety Assessment Protocol for Mars Sample Return

Martian rock and regolith samples are being collected and cached by NASA’s Perseverance rover, with the goal of returning them to Earth as soon as the mid-2030s. Upon return, samples would be housed in a sample receiving facility under biological containment to prevent exposing Earth’s biosphere to any potential biohazards that might be present. Samples could be released from high containment for scientific investigations if they are found to be safe or are sterilized. The Sample Safety Assessment Protocol Tiger Team (SSAP-TT) was convened by the Sample Receiving Project between August 2023 and August 2024 and tasked with the development of a Sample Safety Assessment Protocol (SSAP). The result of this work is a proposed three-step protocol, supported by Bayesian statistical hypothesis testing, to assess the risk as to whether returned samples contain modern martian biology that could represent a biohazard. The proposed protocol outlines procedures to determine whether the samples could be safely released from high containment without sterilization or require a “hold and review” step. This article presents the central concept of the SSAP approach—comparing returned samples to the abiotic baseline. Organic molecules, which exist throughout the solar system, can have either biotic or abiotic origins. However, biotically produced organic molecules exhibit distinct complexity, distribution, and abundance characteristics that differentiate them from those formed through abiotic chemistry. The proposed protocol would examine the organic inventory of returned samples by using multiple techniques, including morphological and spectral assessments, to determine whether any signals exceed the abiotic baseline; that is, whether the organic molecular inventory could be explained solely by abiotic chemical synthesis. This approach provides a rigorous, yet feasible, safety assessment protocol by using modern techniques while minimizing sample consumption. We also identify key areas for future research and development, which include detection limits and further characterization of the martian abiotic background.

Astrobiology↗
USGS2025

Planning considerations related to contamination control for the return and analysis of Martian samples

The joint National Aeronautics and Space Administration and European Space Agency Mars Sample Return (MSR) Campaign is a proposed multi-mission effort to bring selected geological samples from Mars to Earth for the purpose of scientific investigation. Significant parts of these investigations could be affected by Earth-sourced contamination that is either misinterpreted as having a martian origin or that masks a martian signal. The Mars 2020 Perseverance rover implemented strict contamination control requirements to limit contamination of the samples during sample collection. Contamination control and contamination knowledge requirements have not yet been established for the samples after they arrive on Earth. The MSR Sample Receiving Facility (SRF) Contamination Panel (SCP) was tasked with defining the terrestrial biological, organic, and inorganic contamination limits for martian samples during their residence inside the SRF. To reach our recommendations, the SCP studied (i) the previously proposed limits and rationale of the Organic Contamination Panel, (ii) cleanliness levels achieved for sampling hardware by the M2020 mission, (iii) recent improvements in analytical technology and detection limits, (iv) updated information regarding the organic content of martian samples ( e.g. , from the Sample Analysis at Mars instrument on the Curiosity rover and laboratory analyses of martian meteorites), and (v) information about the composition and geologic context of samples being collected by the Perseverance rover for return to Earth.

Astrobiology↗
USGS2025

Sample Science Traceability Matrix (SSTM) for Perseverance’s Mars sample return collection

The Mars Sample Return (MSR) Campaign aims to retrieve a set of carefully selected and documented samples collected by NASA’s Perseverance rover in and around Jezero Crater on Mars and deliver this set to Earth for comprehensive laboratory analyses. To emphasize the immense scientific return of this unique collection, this work presents a Sample Science Traceability Matrix (SSTM), a systematic framework that aligns each sample with the MSR campaign’s defined science objectives, subobjectives, and critical research questions. The SSTM explicitly connects prioritized goals—including geologic history, astrobiology, planetary evolution, and human exploration science—to each of the individual samples gathered in and around Jezero Crater on Mars. This matrix offers a structured, quantitative method to assess each sample’s capacity to address key scientific questions, while highlighting synergies across the sample suite and showcasing the overall value of the collection. The SSTM provides a valuable tool for guiding future sample analyses and identifying the most impactful samples that could be collected in the future to complete the set collected by the Mars 2020 mission. It also supports the next phase of Mars sample science and informs strategies for future Mars exploration missions.

Astrobiology↗
USGS2023

Report of the Science Community Workshop on the proposed First Sample Depot for the Mars Sample Return Campaign

The Mars 2020/Mars Sample Return (MSR) Sample Depot Science Community Workshop was held on September 28 and 30, 2022, to assess the Scientifically-Return Worthy (SRW) value of the full collection of samples acquired by the rover Perseverance at Jezero Crater, and of a proposed subset of samples to be left as a First Depot at a location within Jezero Crater called Three Forks. The primary outcome of the workshop was that the community is in consensus on the following statement: The proposed set of ten sample tubes that includes seven rock samples, one regolith sample, one atmospheric sample, and one witness tube constitutes a SRW collection that: (1) represents the diversity of the explored region around the landing site, (2) covers partially or fully, in a balanced way, all of the International MSR Objectives and Samples Team scientific objectives that are applicable to Jezero Crater, and (3) the analyses of samples in this First Depot on Earth would be of fundamental importance, providing a substantial improvement in our understanding of Mars. At the conclusion of the meeting, there was overall community support for forming the First Depot as described at the workshop and placing it at the Three Forks site. The community also recognized that the diversity of the Rover Cache (the sample collection that remains on the rover after placing the First Depot) will significantly improve with the samples that are planned to be obtained in the future by the Perseverance rover and that the Rover Cache is the primary target for MSR to return to Earth.

Meteoritics and Planetary Science↗
USGS2015

Association of anatase (TiO2) and microbes: unusual fossilization effect or a potential biosignature?

We combined microbial paleontology and molecular biology methods to study the Eyreville B drill core from the 35.3-Ma-old Chesapeake Bay impact structure,Virginia, USA. The investigated sample is a pyrite vein collected from the 1353.81-1353.89 m depth interval, located within a section of biotite granite. The granite is a pre-impact rock that was disrupted by the impact event. A search for inorganic (mineral) biosignatures revealed the presence of micron-size rod morphologies of anatase (TiO2) embedded in chlorite coatings on pyrite grains. Neither the Acridine Orange microbial probe nor deoxyribonucleic acid (DNA) extraction followed by polymerase chain reaction (PCR) amplifi cation showed the presence of DNA or ribonucleic acid (RNA) at the location of anatase rods, implying the absence of viable cells in the investigated area. A Nile Red microbial probe revealed the presence of lipids in the rods. Because most of the lipids are resistant over geologic time spans, they are good biomarkers, and they are an indicator of biogenicity for these possibly 35-Ma-old microbial fossils. The mineral assemblage suggests that rod morphologies are associated with low-temperature (<100 &deg;C) hydrothermal alteration that involved aqueous fl uids. The temporal constraints on the anatase fossils are still uncertain because pre-impact alteration of the granite and postimpact heating may have provided identical conditions for anatase precipitation and microbial preservation.

Geological Society of America Bulletin↗
USGS2013

Microbial community composition and endolith colonization at an Arctic thermal spring are driven by calcite precipitation

Environmental conditions shape community composition. Arctic thermal springs provide an opportunity to study how environmental gradients can impose strong selective pressures on microbial communities and provide a continuum of niche opportunities. We use microscopic and molecular methods to conduct a survey of microbial community composition at Troll Springs on Svalbard, Norway, in the high Arctic. Microorganisms there exist under a wide range of environmental conditions: in warm water as periphyton, in moist granular materials, and in cold, dry rock as endoliths. Troll Springs has two distinct ecosystems, aquatic and terrestrial, together in close proximity, with different underlying environmental factors shaping each microbial community. Periphyton are entrapped during precipitation of calcium carbonate from the spring's waters, providing microbial populations that serve as precursors for the development of endolithic communities. This process differs from most endolith colonization, in which the rock predates the communities that colonize it. Community composition is modulated as environmental conditions change within the springs. At Troll, the aquatic environments show a small number of dominant operational taxonomic units (OTUs) that are specific to each sample. The terrestrial environments show a more even distribution of OTUs common to multiple samples.

Environmental Microbiology Reports↗