Reply to Bada: Acidity and fluid composition on the Tagish Lake parent body

A comment from Bada (1) attempts to flag multiple issues with our recent study (2). We appreciate the opportunity to respond, as Bada raises some interesting points, but many of his comments appear to overinterpret our results in a manner well beyond the scope of our original study. We believe Bada’s comments (1) can be broadly grouped into two key points for discussion: 1) the calculation used to yield the racemization timeline and 2) issues with our final conclusion

Reply to Bada: Acidity and fluid composition on the Tagish Lake parent body

A comment from Bada (1) attempts to flag multiple issues with our recent study (2). We appreciate the opportunity to respond, as Bada raises some interesting points, but many of his comments appear to overinterpret our results in a manner well beyond the scope of our original study. We believe Bada’s comments (1) can be broadly grouped into two key points for discussion: 1) the calculation used to yield the racemization timeline and 2) issues with our final conclusion

Evidence for Sodium-Rich Alkaline Water in the Tagish Lake Parent Body and Implications for Amino Acid Synthesis and Racemization

Understanding the timing and mechanisms of amino acid synthesis and racemization on asteroidal parent bodies is key to demonstrating how amino acids evolved to be mostly left-handed in living organisms on Earth. It has been postulated that racemization can occur rapidly dependent on several factors, including the pH of the aqueous solution. Here, we conduct nanoscale geochemical analysis of a framboidal magnetite grain within the Tagish Lake carbonaceous chondrite to demonstrate that the interlocking crystal arrangement formed within a sodium-rich, alkaline fluid environment. Notably, we report on the discovery of Na-enriched subgrain boundaries and nanometer-scale Ca and Mg layers surrounding individual framboids. These interstitial coatings would yield a surface charge state of zero in more-alkaline fluids and prevent assimilation of the individual framboids into a single grain. This basic solution would support rapid synthesis and racemization rates on the order of years, suggesting that the low abundances of amino acids in Tagish Lake cannot be ascribed to fluid chemistry

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

Detailed Mineralogical and Petrological Analysis of Martian Shergottite NWA 6342

NWA 6342 is an intermediate, ultramafic, poikilitic shergottite that was found in Algeria in 2010. As the poikilitic shergottite-group meteorites are thought to have originated from the same slow-cooling magma chamber, studying samples like NWA 6342 provides us with the unique opportunity to reconstruct and analyze an igneous body on Mars, diversifying our knowledge of volcanic and impact processes in our Solar System. The relatively homogeneous composition of the forsterite grains in NWA 6342 indicates that it was located at an intermediate level within the original magma chamber. The lack of maskelynite, and complete recrystallization of plagioclase observed in the sample also indicate that it was subjected to a higher degree of post-impact thermal metamorphism than the other poikilitic shergottites, and may have experienced two impact events. This could explain how these ultramafic rocks could have been relocated close enough to the surface to be ejected to Earth.M.Sc

Statistical Characterization of PIXL Trace Element Detection Limits

Trace element detection and mapping are some of the key capabilities of the Planetary Instrument for X-ray Lithochemistry (PIXL) on board the Mars 2020 rover Perseverance. However, poor signal-to-noise ratios due to the short integration times required to make high-spatial-resolution map scans operationally feasible raise the possibility of misidentifying statistical noise as a signal from a trace element, which can cause a large number of false detections of a trace element among the hundreds to thousands of data points in each PIXL scan. Here, we apply a statistical technique to quantify the likelihood of such misidentifications and determine what concentration of a trace element must be present to reach statistical confidence in a detection. This approach is anticipated to be applicable both when analyzing existing PIXL data to ensure that noise is not misinterpreted as signals from trace elements and operationally as a tool to inform scan parameters when trace elements of interest are anticipated to be present

Alteration history of Séítah formation rocks inferred by PIXL x-ray fluorescence, x-ray diffraction, and multispectral imaging on Mars.

Collocated crystal sizes and mineral identities are critical for interpreting textural relationships in rocks and testing geological hypotheses, but it has been previously impossible to unambiguously constrain these properties using in situ instruments on Mars rovers. Here, we demonstrate that diffracted and fluoresced x-rays detected by the PIXL instrument (an x-ray fluorescence microscope on the Perseverance rover) provide information about the presence or absence of coherent crystalline domains in various minerals. X-ray analysis and multispectral imaging of rocks from the Séítah formation on the floor of Jezero crater shows that they were emplaced as coarsely crystalline igneous phases. Olivine grains were then partially dissolved and filled by finely crystalline or amorphous secondary silicate, carbonate, sulfate, and chloride/oxychlorine minerals. These results support the hypothesis that Séítah formation rocks represent olivine cumulates altered by fluids far from chemical equilibrium at low water-rock ratios

Overview and Results From the Mars 2020 Perseverance Rover's First Science Campaign on the Jezero Crater Floor

International audienceThe Mars 2020 Perseverance rover landed in Jezero crater on 18 February 2021. After a 100-sol period of commissioning and the Ingenuity Helicopter technology demonstration, Perseverance began its first science campaign to explore the enigmatic Jezero crater floor, whose igneous or sedimentary origins have been much debated in the scientific community. This paper describes the campaign plan developed to explore the crater floor's Máaz and Séítah formations and summarizes the results of the campaign between sols 100-379. By the end of the campaign, Perseverance had traversed more than 5 km, created seven abrasion patches, and sealed nine samples and a witness tube. Analysis of remote and proximity science observations show that the Máaz and Séítah formations are igneous in origin and composed of five and two geologic members, respectively. The Séítah formation represents the olivine-rich cumulate formed from differentiation of a slowly cooling melt or magma body, and the Máaz formation likely represents a separate series of lava flows emplaced after Séítah. The Máaz and Séítah rocks also preserve evidence of multiple episodes of aqueous alteration in secondary minerals like carbonate, Fe/Mg phyllosilicates, sulfates, and perchlorate, and surficial coatings. Post-emplacement processes tilted the rocks near the Máaz-Séítah contact and substantial erosion modified the crater floor rocks to their present-day expressions. Results from this crater floor campaign, including those obtained upon return of the collected samples, will help to build the geologic history of events that occurred in Jezero crater and provide time constraints on the formation of the Jezero delta. Plain Language Summary The Mars 2020 Perseverance rover, along with the Ingenuity Helicopter technology demonstration, landed in Jezero crater, Mars on 18 February 2021. Here, we detail results from the first science campaign of the mission, the purpose of which was to explore the enigmatic Jezero crater floor. By the end of the campaign, Perseverance traversed more than 5 km, created seven abrasion patches, SUN ET AL