Interplanetary dust particles (IDPs) and micrometeorites (MMs) were likely major sources of extraterrestrial organics at the surface of the early Earth. However, these particles experience heating to >500 degrees C for up to several seconds during atmospheric entry. In this study, we aim to understand the effects of atmospheric entry heating on the dominant organic component in IDPs and MMs by conducting flash heating experiments (4 s to 400 degrees C, 600 degrees C, 800 degrees C, and 1000 degrees C) on insoluble organic matter (IOM) extracted from the meteorite Cold Bokkeveld (CM2). For each of the experimental charges, the bulk isotopic compositions of H, N, and C were analyzed by IRMS, the H isotopic heterogeneities (occurrence of deuterium hotspots) of the samples were measured by NanoSIMS, and the functional group chemistry and ordering of the IOM was evaluated by using FTIR and Raman spectroscopy, respectively. Organic matter in particles heated to >= 600 degrees C during atmospheric entry experienced significant alteration. Loss of isotopically heavy, labile H and N groups results in decreases in bulk delta D, delta N-15, H/C and, upon heating >= 800 degrees C, in N/C. The H isotopic heterogeneity was not greatly affected by flash heating to <= 600 degrees C, although the hotspots tended to be less isotopically anomalous in the 600 degrees C sample than in the 400 degrees C sample. However, the hotspots all but disappeared in the 800 degrees C sample. Loss of C=O groups occurred at 800 degrees C. Based on the Raman G-band characteristics, the heating resulted in increased ordering of the polyaromatic component of the IOM.

The X-Ray Spectrometer (XRS) on the MESSENGER spacecraft provided measurements of major-element ratios across Mercury's surface. We present global maps of Mg/Si, Al/Si, S/Si, Ca/Si, and Fe/Si derived from XRS data collected throughout MESSENGER's orbital mission. We describe the procedures we used to select and filter data and to combine them to make the final maps, which are archived in NASA's Planetary Data System. Areal coverage is variable for the different element-ratio maps, with 100% coverage for Mg/Si and Al/Si, but only 18% coverage for Fe/Si north of 30 degrees N, where the spatial resolution is highest. The spatial resolution is improved over previous maps by 10-15% because of the inclusion of higher-resolution data from late in the mission when the spacecraft periapsis altitude was low. Unlike typical planetary data maps, however, the spatial resolution of the XRS maps can vary from pixel to pixel, and thus care must be taken in interpreting small-scale features. We provide several examples of how the XRS maps can be used to investigate elemental variations in the context of geological features on Mercury, which range in size from single similar to 100-km-diameter craters to large impact basins. We expect that these maps will provide the basis for and/or contribute to studies of Mercury's origin and geological history for many years to come.

We built a collector to filter interplanetary dust particles (IDPs) larger than 5 mu m from the clean air at the Amundsen Scott South Pole station. Our sampling strategy used long duration, continuous dry filtering of near-surface air in place of short duration, high-speed impact collection on flags flown in the stratosphere. We filtered similar to 10(7) m(3) of clean Antarctic air through 20 cm diameter, 3 mu m filters coupled to a suction blower of modest power consumption (5-6 kW). Our collector ran continuously for 2 years and yielded 41 filters for analyses. Based on stratospheric concentrations, we predicted that each month's collection would provide 300-900 IDPs for analysis. We identified 19 extraterrestrial (ET) particles on the 66 cm(2) of filter examined, which represented similar to 0.5% of the exposed filter surfaces. The 11 ET particles larger than 5 mu m yield about a fifth of the expected flux based on >5 mu m stratospheric ET particle flux. Of the 19 ET particles identified, four were chondritic porous IDPs, seven were FeNiS beads, two were FeNi grains, and six were chondritic material with FeNiS components. Most were <10 mu m in diameter and none were cluster particles. Additionally, a carbon-rich candidate particle was found to have a small N-15 isotopic enrichment, supporting an ET origin. Many other candidate grains, including chondritic glasses and C-rich particles with Mg and Si and FeS grains, require further analysis to determine if they are ET. The vast majority of exposed filter surfaces remain to be examined.

Planetary remote-sensing instruments are often required to cover a relatively large field of view, ideally with a uniform angular resolution over the field, due to relatively large apparent sizes of planetary targets at close proximities. They also have to comply with relatively tight mass and volume constraints. For these reasons, planetary x-ray telescopes in the past were mainly collimation-based x-ray spectrometers without focusing optics. Recent advances in x-ray optics technology now enable compact focusing x-ray telescopes suitable for planetary science (e.g., BepiColombo). We present two design options for compact Wolter-I x-ray optics for a SmallSat lunar mission concept-the CubeSat X-ray telescope (CubeX). The primary objectives of CubeX are to map surface elemental abundances of selected lunar impact craters and to assess the feasibility of millisecond x-ray pulsar timing navigation in realistic deep space navigation environments. The Miniature X-ray Optics (MiXO) in CubeX utilizes electroformed NiCo alloy replication (ENR) technology, which provides many advantages over micro-pore optics (MPO) employed in BepiColombo. We carry out extensive ray traces over a grid of mirror parameters and explore a novel tapered shaped design of tightly nested shells, where both shell length and focal-plane offsets vary with shell diameter. One of the two configurations is optimized for large effective areas at low energies, while the other for lower mass and high-energy response. We compare their performances with those of conventional designs through the spatial resolution and effective area estimated by ray traces. (C) 2020 Optical Society of America

Effects of aqueous alteration on primordial noble gas carriers were investigated by analyzing noble gases and determining presolar SiC abundances in insoluble organic matter (IOM) from four Tagish Lake meteorite (C2-ung.) samples that experienced different degrees of aqueous alteration. The samples contained a mixture of primordial noble gases from phase Q and presolar nanodiamonds (HL, P3), SiC (Ne-E[H]), and graphite (Ne-E[L]). The second most altered sample (11i) had a similar to 2-3 times higher Ne-E concentration than the other samples. The presolar SiC abundances in the samples were determined from NanoSIMS ion images and 11i had a SiC abundance twice that of the other samples. The heterogeneous distribution of SiC grains could be inherited from heterogeneous accretion or parent body alteration could have redistributed SiC grains. Closed system step etching (CSSE) was used to study noble gases in HNO3-susceptible phases in the most and least altered samples. All Ne-E carried by presolar SiC grains in the most altered sample was released during CSSE, while only a fraction of the Ne-E was released from the least altered sample. This increased susceptibility to HNO3 likely represents a step toward degassing. Presolar graphite appears to have been partially degassed during aqueous alteration. Differences in the He-4/Ar-36 and Ne-20/Ar-36 ratios in gases released during CSSE could be due to gas release from presolar nanodiamonds, with more He and Ne being released in the more aqueously altered sample. Aqueous alteration changes the properties of presolar grains so that they react similar to phase Q in the laboratory, thereby altering the perceived composition of Q.

We report a correlated NanoSIMS-transmission electron microscopy study of the ungrouped carbonaceous chondrite Northwest Africa (NWA) 5958. We identified 10 presolar SiC grains, 2 likely presolar graphite grains, and 20 presolar silicate and/or oxide grains in NWA 5958. We suggest a slight modification of the commonly used classification system for presolar oxides and silicates that better reflects the grains' likely stellar origins. The matrix-normalized presolar SiC abundance in NWA 5958 is 18-10+15 ppm (2 sigma) similar to that seen in many classes of unmetamorphosed chondrites. In contrast, the matrix-normalized abundance of presolar O-rich phases (silicates and oxides) is 30.9-13.1+17.8 ppm (2 sigma), much lower than seen in interplanetary dust particles and the least-altered CR, CO, and ungrouped C chondrites, but close to that reported for CM chondrites. NanoSIMS mapping also revealed an unusual C-13-enriched (delta C-13 approximate to 100-200 parts per thousand) carbonaceous rim surrounding a 1.4 mu m diameter phyllosilicate grain. Transmission electron microscopy (TEM) analysis of two presolar grains with a likely origin in asymptotic giant branch stars identified one as enstatite and one as Al-Mg spinel with minor Cr. The enstatite grain amorphized rapidly under the electron beam, suggesting partial hydration. TEM data of NWA 5958 matrix confirm that it has experienced aqueous alteration and support the suggestion of Jacquet et al. (34) that this meteorite has affinities to CM2 chondrites.

Stardust grains that originated in ancient stars and supernovae are recovered from meteorites and carry the detailed composition of their astronomical sites of origin. We present evidence that the majority of large (mu m-sized) meteoritic silicon carbide (SiC) grains formed in C-rich asymptotic giant branch (AGB) stars that were more metal-rich than the Sun. In the framework of the slow neutron captures (thesprocess) that occur in AGB stars, the lower-than-solars-process nucleosynthesis variations observed in bulk meteorites. In the outflows of metal-rich, C-rich AGB stars, SiC grains are predicted to be small (0.2 mu m); large (mu m-sized) SiC grains can grow if the number of dust seeds is 2-3 orders of magnitude lower than the standard value of 10(-13)times the number of H atoms. We therefore predict that with increasing metallicity, the number of dust seeds might decrease, resulting in the production of larger SiC grains.

The Asuka (A)-12236 meteorite has recently been classified as a CM carbonaceous chondrite of petrologic type 3.0/2.9 and is among the most primitive CM meteorites studied to date. Here, we report the concentrations, relative distributions, and enantiomeric ratios of amino acids in water extracts of the A-12236 meteorite and another primitive CM chondrite Elephant Moraine (EET) 96029 (CM2.7) determined by ultra-high-performance liquid chromatography time-of-flight mass spectrometry. EET 96029 was highly depleted in amino acids and dominated by glycine, while a wide diversity of two- to six-carbon aliphatic primary amino acids were identified in A-12236, which had a total amino acid abundance of 360 +/- 18 nmol g(-1), with most amino acids present without hydrolysis (free). The amino acid concentrations of A-12236 were double those previously measured in the CM2.7 Paris meteorite, consistent with A-12236 being a highly primitive and unheated CM chondrite. The high relative abundance of alpha-amino acids in A-12236 is consistent with formation by a Strecker-cyanohydrin dominated synthesis during a limited early aqueous alteration phase on the CM meteorite parent body. The presence of predominantly free glycine, a near racemic mixture of alanine (d/l similar to 0.93-0.96), and elevated abundances of several terrestrially rare non-protein amino acids including alpha-aminoisobutyric acid (alpha-AIB) and racemic isovaline indicate that these amino acids in A-12236 are extraterrestrial in origin. Given a lack of evidence for biological amino acid contamination in A-12236, it is possible that some of thel-enantiomeric excesses (l(ee) similar to 34-64%) of the protein amino acids, aspartic and glutamic acids and serine, are indigenous to the meteorite; however, isotopic measurements are needed for confirmation. In contrast to more aqueously altered CMs of petrologic types <= 2.5, nol-isovaline excesses were detected in A-12236. This observation strengthens the hypothesis that extensive parent body aqueous activity is required to produce or amplify the largel-isovaline excesses that cannot be explained solely by exposure to circularly polarized radiation or other chiral symmetry breaking mechanisms prior to incorporation into the asteroid parent body.

BepiColombo has a larger and in many ways more capable suite of instruments relevant for determination of the topographic, physical, chemical and mineralogical properties of Mercury's surface than the suite carried by NASA's MESSENGER spacecraft. Moreover, BepiColombo's data rate is substantially higher. This equips it to confirm, elaborate upon, and go beyond many of MESSENGER's remarkable achievements. Furthermore, the geometry of BepiColombo's orbital science campaign, beginning in 2026, will enable it to make uniformly resolved observations of both northern and southern hemispheres. This will offer more detailed and complete imaging and topographic mapping, element mapping with better sensitivity and improved spatial resolution, and totally new mineralogical mapping. We discuss MESSENGER data in the context of preparing for BepiColombo, and describe the contributions that we expect BepiColombo to make towards increased knowledge and understanding of Mercury's surface and its composition. Much current work, including analysis of analogue materials, is directed towards better preparing ourselves to understand what BepiColombo might reveal. Some of MESSENGER's more remarkable observations were obtained under unique or extreme conditions. BepiColombo should be able to confirm the validity of these observations and reveal the extent to which they are representative of the planet as a whole. It will also make new observations to clarify geological processes governing and reflecting crustal origin and evolution. We anticipate that the insights gained into Mercury's geological history and its current space weathering environment will enable us to better understand the relationships of surface chemistry, morphologies and structures with the composition of crustal types, including the nature and mobility of volatile species. This will enable estimation of the composition of the mantle from which the crust was derived, and lead to tighter constraints on models for Mercury's origin including the nature and original heliocentric distance of the material from which it formed.