The <i>Rosetta</i> Mission and the Chemistry of Organic Species in Comet 67P/Churyumov–Gerasimenko

Comets are regarded as probably the most primitive of solar system objects, preserving a record of the materials from which the solar system aggregated. Key amongst their components are organic compounds – molecules that may trace their heritage to the interstellar medium from which the protosolar nebula eventually emerged. The most recent cometary space mission, Rosetta, carried instruments designed to characterize, in unprecedented detail, the organic species in comet 67P/Churyumov–Gerasimenko (67P). Rosetta was the first mission to match orbits with a comet and follow its evolution over time, and also the first mission to land scientific instruments on a comet surface. Results from the mission revealed a greater variety of molecules than previously identified and indicated that 67P contained both primitive and processed organic entities

COSIMA-Rosetta calibration for in-situ characterization of 67P/Churyumov-Gerasimenko cometary inorganic compounds

20 pages, 3 figures, 5 tablesInternational audienceCOSIMA (COmetary Secondary Ion Mass Analyser) is a time-of-flight secondary ion mass spectrometer (TOF-SIMS) on board the Rosetta space mission. COSIMA has been designed to measure the composition of cometary dust grains. It has a mass resolution m/{\Delta}m of 1400 at mass 100 u, thus enabling the discrimination of inorganic mass peaks from organic ones in the mass spectra. We have evaluated the identification capabilities of the reference model of COSIMA for inorganic compounds using a suite of terrestrial minerals that are relevant for cometary science. Ground calibration demonstrated that the performances of the flight model were similar to that of the reference model. The list of minerals used in this study was chosen based on the mineralogy of meteorites, interplanetary dust particles and Stardust samples. It contains anhydrous and hydrous ferromagnesian silicates, refractory silicates and oxides (present in meteoritic Ca-Al-rich inclusions), carbonates, and Fe-Ni sulfides. From the analyses of these minerals, we have calculated relative sensitivity factors for a suite of major and minor elements in order to provide a basis for element quantification for the possible identification of major mineral classes present in the cometary grains

Similarities in element content between comet 67P/Churyumov–Gerasimenko coma dust and selected meteorite samples

We have analysed the element composition and the context of particles collected within the coma of 67P/Churyumov–Gerasimenko with Rosetta’s COmetary Secondary Ion Mass Analyzer (COSIMA). A comparison has been made between on board cometary samples and four meteorite samples measured in the laboratory with the COSIMA reference model. Focusing on the rock-forming elements, we have found similarities with chondrite meteorites for some ion count ratios. The composition of 67P/Churyumov–Gerasimenko particles measured by COSIMA shows an enrichment in volatile elements compared to that of the investigated Renazzo (CR2) carbonaceous meteorite sample.</p

Nitrogen-to-carbon atomic ratio measured by COSIMA in the particles of comet 67P/Churyumov–Gerasimenko

The COmetary Secondary Ion Mass Analyzer (COSIMA) on board the Rosetta mission has analysed numerous cometary dust particles collected at very low velocities (a few m s−1) in the environment of comet 67P/Churyumov–Gerasimenko (hereafter 67P). In these particles, carbon and nitrogen are expected mainly to be part of the organic matter. We have measured the nitrogen-to-carbon (N/C) atomic ratio of 27 cometary particles. It ranges from 0.018 to 0.06 with an averaged value of 0.035 ± 0.011. This is compatible with the measurements of the particles of comet 1P/Halley and is in the lower range of the values measured in comet 81P/Wild 2 particles brought back to Earth by the Stardust mission. Moreover, the averaged value found in 67P particles is also similar to the one found in the insoluble organic matter extracted from CM, CI and CR carbonaceous chondrites and to the bulk values measured in most interplanetary dust particles and micrometeorites. The close agreement of the N/C atomic ratio in all these objects indicates that their organic matters share some similarities and could have a similar chemical origin. Furthermore, compared to the abundances of all the detected elements in the particles of 67P and to the elemental solar abundances, the nitrogen is depleted in the particles and the nucleus of 67P as was previously inferred also for comet 1P/Halley. This nitrogen depletion could constrain the formation scenarios of cometary nuclei.</p

COSPAR Sample Safety Assessment Framework (SSAF)

The Committee on Space Research (COSPAR) Sample Safety Assessment Framework (SSAF) has been developed by a COSPAR appointed Working Group. The objective of the sample safety assessment would be to evaluate whether samples returned from Mars could be harmful for Earth's systems (e.g., environment, biosphere, geochemical cycles). During the Working Group's deliberations, it became clear that a comprehensive assessment to predict the effects of introducing life in new environments or ecologies is difficult and practically impossible, even for terrestrial life and certainly more so for unknown extraterrestrial life. To manage expectations, the scope of the SSAF was adjusted to evaluate only whether the presence of martian life can be excluded in samples returned from Mars. If the presence of martian life cannot be excluded, a Hold & Critical Review must be established to evaluate the risk management measures and decide on the next steps. The SSAF starts from a positive hypothesis (there is martian life in the samples), which is complementary to the null-hypothesis (there is no martian life in the samples) typically used for science. Testing the positive hypothesis includes four elements: (1) Bayesian statistics, (2) subsampling strategy, (3) test sequence, and (4) decision criteria. The test sequence capability covers self-replicating and non-self-replicating biology and biologically active molecules. Most of the investigations associated with the SSAF would need to be carried out within biological containment. The SSAF is described in sufficient detail to support planning activities for a Sample Receiving Facility (SRF) and for preparing science announcements, while at the same time acknowledging that further work is required before a detailed Sample Safety Assessment Protocol (SSAP) can be developed. The three major open issues to be addressed to optimize and implement the SSAF are (1) setting a value for the level of assurance to effectively exclude the presence of martian life in the samples, (2) carrying out an analogue test program, and (3) acquiring relevant contamination knowledge from all Mars Sample Return (MSR) flight and ground elements. Although the SSAF was developed specifically for assessing samples from Mars in the context of the currently planned NASA-ESA MSR Campaign, this framework and the basic safety approach are applicable to any other Mars sample return mission concept, with minor adjustments in the execution part related to the specific nature of the samples to be returned. The SSAF is also considered a sound basis for other COSPAR Planetary Protection Category V, restricted Earth return missions beyond Mars. It is anticipated that the SSAF will be subject to future review by the various MSR stakeholders

Aqueous alteration processes in Jezero crater, Mars—implications for organic geochemistry

The Perseverance rover landed in Jezero crater, Mars, in February 2021. We used the Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) instrument to perform deep-ultraviolet Raman and fluorescence spectroscopy of three rocks within the crater. We identify evidence for two distinct ancient aqueous environments at different times. Reactions with liquid water formed carbonates in an olivine-rich igneous rock. A sulfate-perchlorate mixture is present in the rocks, which probably formed by later modifications of the rocks by brine. Fluorescence signatures consistent with aromatic organic compounds occur throughout these rocks and are preserved in minerals related to both aqueous environments

ToF-SIMS-analys av enskilda vätskeinneslutningar : Implikationer för studier av tidiga jordens biodiveristet och paleomiljö

When and how life first emerged on the Earth is an area of intense research. Signs of the first life on Earth, including morphological fossils, are scarce and hard to interpret. An alternative approach is to study organic biomarkers, which are molecular fossils commonly considered as bona fide biosignatures. The main objective of the project is to develop an approach for analysis of single oil-bearing fluid inclusions and most importantly the detection of organic biomarkers in these inclusions. Analysis of oil-bearing fluid inclusions is advantageous since the inclusions may provide an uncontaminated sample source of Precambrian hopanes and steranes, which are key biomarkers for tracing the early evolution of life on Earth. Due to the presence of several inclusion generations, single inclusion analysis is desired in order to constrain biomarkers to specific inclusions. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) could be an excellent tool for analysis of these types of samples. The development of the approach for analysis of single oil-bearing inclusions was done in a two-step process; i) a number of crude oils were analysed with ToF-SIMS and gas chromatography mass-spectrometry (GC-MS) to facilitate interpretation of ToF-SIMS spectra of these types of samples and, ii) a procedure that combines micrographs with ion etching and ToF-SIMS analysis was developed for analysis of inclusions. The feasibility of the technique was demonstrated for oil inclusions from the Siljan impact crater in which hopanes and steranes where detected. Single oil-bearing fluid inclusions trapped in mid-Proterozoic sandstones from Northern Australia were subsequently analyzed, and steranes and hopanes were detected in these inclusions. If applied on older inclusions this approach may help answer some of the questions regarding the emergence and evolution of life on Earth, and if applied on extraterrestrial samples, also the possibility of life on other planets and moons.Livets uppkomst och tidiga utveckling på jorden är ett hett forskningsfält. Hur och när livet och dess olika domäner (arkéer, bakterier och eukaryoter) uppstod på jorden är fortfarande oklart vilket beror på att de första tecknen på liv, vilka inkluderar morfologiska fossil, spårfossil och isotoper, är få och svåra att tolka. Ett alternativt sätt att studera det tidiga livet är att studera organiska biomarkörer som är organiska molekyler som anses unika för liv. Huvudmålet med projektet är att utveckla en metod som kan detektera organiska biomarkörer i enskilda oljebärande vätskeinneslutningar. Vätskeinneslutningar, som är små mängder vätska (picoliter) infångad in en sten, är intressanta då de är en potentiell provkälla för prekambriska (äldre än 500 miljoner år) biomarkörer, som hopaner och steraner, vilka används för att utforska livets tidiga utveckling på jorden. Analys av enskilda inneslutningar är emellertid oftast nödvändigt för att kunna tidsavgränsa biomarkörer. På grund av att de flesta inneslutningar är små (10 µm i diameter) är det inte möjligt att analysera en enskild vätskeinneslutning med standardtekniken gaskromatografi-masspektrometri (GC-MS). Time-of-flight secondary ion mass spektrometri (ToF-SIMS) med sin höga känslighet, höga massupplösning och kapacitet för 2D-representation av analysdata och djupprofilering av prover är en utmärkt teknik för analys av enskilda inneslutningar. Metoden för analys av enskilda inneslutningar utvecklades i två steg. Först analyserades ett antal råoljor med ToF-SIMS och GC-MS för att underlätta förståelsen av ToF-SIMS-spektra från dessa typer av prover. Därefter utvecklades en metod som bestod av mikroskopering för att lokalisera inneslutningen, jonetsning för att öppna inneslutningen och ToF-SIMS analys av det exponerade innehållet. Metoden testades framgångsrikt på enskilda inneslutningar i hydrotermala vener av flusspat och kalcit i ordovicisk (488-443 miljoner år sedan) kalksten. Därefter användes den utvecklade metoden för att analysera enskilda vätskeinneslutningar i 1,43 miljarder år gammal sandsten från norra Australien, i vilka hopaner och steraner detekterades. De detekterade steranerna visar att trots att havet under denna tid var syrefritt existerade det lokala syrerika miljöer där eukaryoter kunde överleva. Om den utvecklade metoden används på ännu äldre inneslutningar, vilka har daterats till 3,2 miljarder år, kan den komma att svara på några de mest fundamentala frågorna kring livets uppkomst och tidiga utveckling. Om metoden används på utomjordiska prover kan den svara på frågan om det finns liv på andra planeter eller månar.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Submitted

Evidence of Sulfate-Rich Fluid Alteration in Jezero Crater Floor, Mars

Sulfur plays a major role in martian geochemistry and sulfate minerals are important repositories of water. However, their hydration states on Mars are poorly constrained. Therefore, understanding the hydration and distribution of sulfate minerals on Mars is important for understanding its geologic, hydrologic, and atmospheric evolution as well as its habitability potential. NASA's Perseverance rover is currently exploring the Noachian-age Jezero crater, which hosts a fan-delta system associated with a paleolake. The crater floor includes two igneous units (the Séítah and Máaz formations), both of which contain evidence of later alteration by fluids including sulfate minerals. Results from the rover instruments Scanning Habitable Environments with Raman and Luminescence for Organics and Chemistry and Planetary Instrument for X-ray Lithochemistry reveal the presence of a mix of crystalline and amorphous hydrated Mg-sulfate minerals (both MgSO4·[3–5]H2O and possible MgSO4·H2O), and anhydrous Ca-sulfate minerals. The sulfate phases within each outcrop may have formed from single or multiple episodes of water activity, although several depositional events seem likely for the different units in the crater floor. Textural and chemical evidence suggest that the sulfate minerals most likely precipitated from a low temperature sulfate-rich fluid of moderate pH. The identification of approximately four waters puts a lower constraint on the hydration state of sulfate minerals in the shallow subsurface, which has implications for the martian hydrological budget. These sulfate minerals are key samples for future Mars sample return. Correspondence Address: S. Siljeström; RISE Research Institutes of Sweden, Stockholm, Sweden; email: [email protected]; </p

Depositional and Diagenetic Sulfates of Hogwallow Flats and Yori Pass, Jezero Crater : Evaluating Preservation Potential of Environmental Indicators and Possible Biosignatures From Past Martian Surface Waters and Groundwaters

The Mars 2020 Perseverance rover has examined and sampled sulfate-rich clastic rocks from the Hogwallow Flats member at Hawksbill Gap and the Yori Pass member at Cape Nukshak. Both strata are located on the Jezero crater western fan front, are lithologically and stratigraphically similar, and have been assigned to the Shenandoah formation. In situ analyses demonstrate that these are fine-grained sandstones composed of phyllosilicates, hematite, Ca-sulfates, Fe-Mg-sulfates, ferric sulfates, and possibly chloride salts. Sulfate minerals are found both as depositional grains and diagenetic features, including intergranular cement and vein- and vug-cements. Here, we describe the possibility of various sulfate phases to preserve potential biosignatures and the record of paleoenvironmental conditions in fluid and solid inclusions, based on findings from analog sulfate-rich rocks on Earth. The samples collected from these outcrops, Hazeltop and Bearwallow from Hogwallow Flats, and Kukaklek from Yori Pass, should be examined for such potential biosignatures and environmental indicators upon return to Earth. We thank the entire Mars 2020 science, engineering, and leadership team. K. C. Benison and K. K. Gill acknowledge funding from National Aeronautics and Space Administration Grant 80NSSC20K0235 to K.C.B. T. Bosak is supported by NASA Grant 80NSSC20K0234 and the Simons Foundation Collaboration on the Origins of Life #327126. E. A. Cloutis acknowledges funding from the Canadian Space Agency (Grants 15FASTA05 and 22EXPCOI4), the Natural Sciences and Engineering Research Council of Canada (Grants RGPIN‐2015‐0452, RTI‐2020‐00157, and RGPIN‐2023‐03413), the Canada Foundation for Innovation and Research Manitoba (Grants CFI1504 and CFI‐2450). F. Fornaro was funded through the ASI/INAF Agreement n. 2023‐3‐HH. C. D. K. Herd and N. Randazzo acknowledge funding from the Canadian Space Agency (20EXPMARS), and the Natural Sciences and Engineering Research Council of Canada (Grant RGPIN‐2018‐04902 to C.D.K.H.). J. M. Madariaga and J. M. Frias acknowledge funding from the Spanish Agency for Research AEI/MCIN/FEDER Grant PID2022‐142750OB‐I00. M. Nachon was funded by NASA M2020 Participating Scientist Grant 80NSSC21K0329. S. Sharma, K. Hand, and K. Uckert acknowledge funding from the National Aeronautics and Space Administration (80NM0018D0004) to support research that was carried out at the Jet Propulsion Laboratory, California Institute of Technology. S. Siljeström acknowledges funding from the Swedish National Space Agency, contract 2021‐00092. A. Williams acknowledges funding from NASA 80NSSC21K0332.</p