Extraterrestrial materials, including meteorites, interplanetary dust, and spacecraft-returned asteroidal and cometary samples, provide a record of the starting materials and early evolution of the ...Solar System. We review how laboratory analyses of these materials provide unique information, complementary to astronomical observations, about a wide variety of stellar, interstellar and protoplanetary processes. Presolar stardust grains retain the isotopic compositions of their stellar sources, mainly asymptotic giant branch stars and Type II supernovae. They serve as direct probes of nucleosynthetic and dust formation processes in stars, galactic chemical evolution, and interstellar dust processing. Extinct radioactivities suggest that the Sun's birth environment was decoupled from average galactic nucleosynthesis for some tens to hundreds of Myr but was enriched in short-lived isotopes from massive stellar winds or explosions shortly before or during formation of the Solar System. Radiometric dating of meteorite components tells us about the timing and duration over which solar nebula solids were assembled into the building blocks of the planets. Components of the most primitive meteoritical materials provide further detailed constraints on the formation, processing, and transport of material and associated timescales in the Sun's protoplanetary disk as well as in other forming planetary systems.
2021 Nier Prize for Dr. Nan Liu Nittler, Larry R.
Meteoritics & planetary science,
August 2024, 2024-08-00, 20240801, Letnik:
59, Številka:
S1
Journal Article
X-ray fluorescence spectra obtained by the MESSENGER spacecraft orbiting Mercury indicate that the planet's surface differs in composition from those of other terrestrial planets. Relatively high ...Mg/Si and low Al/Si and Ca/Si ratios rule out a lunarlike feldspar-rich crust. The sulfur abundance is at least 10 times higher than that of the silicate portion of Earth or the Moon, and this observation, together with a low surface Fe abundance, supports the view that Mercury formed from highly reduced precursor materials, perhaps akin to enstatite chondrite meteorites or anhydrous cometary dust particles. Low Fe and Ti abundances do not support the proposal that opaque oxides of these elements contribute substantially to Mercury's low and variable surface reflectance.
On Presolar Stardust Grains from CO Classical Novae Iliadis, Christian; Downen, Lori N.; José, Jordi ...
Astrophysical journal/The Astrophysical journal,
03/2018, Letnik:
855, Številka:
2
Journal Article, Publication
Recenzirano
Odprti dostop
About 30%-40% of classical novae produce dust 20-100 days after the outburst, but no presolar stardust grains from classical novae have been unambiguously identified yet. Although several studies ...claimed a nova paternity for certain grains, the measured and simulated isotopic ratios could only be reconciled, assuming that the grains condensed after the nova ejecta mixed with a much larger amount of close-to-solar matter. However, the source and mechanism of this potential post-explosion dilution of the ejecta remains a mystery. A major problem with previous studies is the small number of simulations performed and the implied poor exploration of the large nova parameter space. We report the results of a different strategy, based on a Monte Carlo technique, that involves the random sampling over the most important nova model parameters: the white dwarf composition; the mixing of the outer white dwarf layers with the accreted material before the explosion; the peak temperature and density; the explosion timescales; and the possible dilution of the ejecta after the outburst. We discuss and take into account the systematic uncertainties for both the presolar grain measurements and the simulation results. Only those simulations that are consistent with all measured isotopic ratios of a given grain are accepted for further analysis. We also present the numerical results of the model parameters. We identify 18 presolar grains with measured isotopic signatures consistent with a CO nova origin, without assuming any dilution of the ejecta. Among these, the grains G270_2, M11-334-2, G278, M11-347-4, M11-151-4, and Ag2_6 have the highest probability of a CO nova paternity.
ABSTRACT
Several observations suggest that the Solar system has been located in a region affected by massive stellar feedback for at least a few Myr; these include detection of live 60Fe in deep-sea ...archives and Antarctic snow, the broad angular distribution of 26Al around the Galactic plane seen in all-sky γ-ray maps, and the all-sky soft X-ray background. However, our position inside the Galactic disc makes it difficult to fully characterize this environment, and our limited time baseline provides no information about its formation history or relation to large-scale galactic dynamics. We explore these questions by using an N-body + hydrodynamics simulation of a Milky-Way-like galaxy to identify stars on Sun-like orbits whose environments would produce conditions consistent with those we observe. We find that such stars are uncommon but not exceptionally rare. These stars are found predominantly near the edges of spiral arms, and lie inside kpc-scale bubbles that are created by multiple generations of star formation in the arm. We investigate the stars’ trajectories and find that the duration of the stay in the bubble ranges from 20 to 90 Myr. The duration is governed by the crossing time of stars across the spiral arm. This is generally shorter than the bubble lifetime, which is ∼100 Myr as a result of the continuous gas supply provided by the arm environment.
The Presolar Grain Database. I. Silicon Carbide Stephan, Thomas; Trappitsch, Reto; Hoppe, Peter ...
The Astrophysical journal. Supplement series,
02/2024, Letnik:
270, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Abstract The Presolar Grain Database (PGD) contains the vast majority of isotope data (published and unpublished) on presolar grains and was first released as a collection of spreadsheets in 2009. It ...has been a helpful tool used by many researchers in cosmochemistry and astrophysics. However, over the years, accumulated errors compromised major parts of the PGD. Here, we provide a fresh start, with the PGD for silicon carbide (SiC) grains rebuilt from the ground up. We also provide updated rules for SiC grain type classification to unify previous efforts, taking into account newly discovered grain types. We also define a new grain type D, which includes some grains previously classified as ungrouped. Future work will focus on rebuilding the PGD for other kinds of presolar grains: graphite, oxides, silicates, and rarer phases.
Measurements by the Neutron Spectrometer on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft show decreases in the flux of epithermal and fast neutrons from ...Mercury's north polar region that are consistent with the presence of water ice in permanently shadowed regions. The neutron data indicate that Mercury's radar-bright polar deposits contain, on average, a hydrogen-rich layer more than tens of centimeters thick beneath a surficial layer 10 to 30 cm thick that is less rich in hydrogen. Combined neutron and radar data are best matched if the buried layer consists of nearly pure water ice. The upper layer contains less than 25 weight % water-equivalent hydrogen. The total mass of water at Mercury's poles is inferred to be 2 × 10 16 to 10 18 grams and is consistent with delivery by comets or volatile-rich asteroids.
MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) orbital observations of Mercury have revealed elevated S abundances, Ca‐S and Mg‐S correlations, and a low upper limit for ...ferrous iron in surface silicates. These data indicate the presence of Ca and/or Mg sulfides in volcanic rocks and a low oxygen fugacity (fO2) in their parental magmas. We have evaluated coupled fO2 and fS2 values and FeO contents in Mercury's magmas from silicate‐sulfide equilibria and empirical models for silicate melts and metallurgical slags. The evaluated fO2 at 1700–1800 K is 4.5 to 7.3 log10 units below the iron‐wüstite buffer. These values correspond to 0.028–0.79 wt % FeO, implying that Fe must be also present in sulfides and metal and are also consistent with the composition of the partial melt of an enstatite chondrite. This derived upper limit for FeO is substantially lower than the limits obtained from reflectance measurements of Mercury's surface materials. The low fO2 and FeO values provide new constraints for igneous processes on Mercury as well as the formation, evolution, and internal structure of the innermost planet.
Key pointsS content in Mercury materials is used to evaluate fO2 and fS2 in magmasThe estimated fO2 is 4.5 to 7.3 log10 units below the iron‐wüstite bufferThe derived upper limit for FeO in magmas and rocks is 0.8 wt %
Multidimensional solid-state NMR spectroscopy is used to refine the identification and abundance determination of functional groups in insoluble organic matter (IOM) isolated from a carbonaceous ...chondrite (Murchison, CM2). It is shown that IOM is composed primarily of highly substituted single ring aromatics, substituted furan/pyran moieties, highly branched oxygenated aliphatics, and carbonyl groups. A pathway for producing an IOM-like molecular structure through formaldehyde polymerization is proposed and tested experimentally. Solid-state 13C NMR analysis of aqueously altered formaldehyde polymer reveals considerable similarity with chondritic IOM. Carbon X-ray absorption near edge structure spectroscopy of formaldehyde polymer reveals the presence of similar functional groups across certain Comet 81P/Wild 2 organic solids, interplanetary dust particles, and primitive IOM. Variation in functional group concentration amongst these extraterrestrial materials is understood to be a result of various degrees of processing in the parent bodies, in space, during atmospheric entry, etc. These results support the hypothesis that chondritic IOM and cometary refractory organic solids are related chemically and likely were derived from formaldehyde polymer. The fine-scale morphology of formaldehyde polymer produced in the experiment reveals abundant nanospherules that are similar in size and shape to organic nanoglobules that are ubiquitous in primitive chondrites.
We present the analysis of 205 spatially resolved measurements of the surface composition of Mercury from MESSENGER's X‐Ray Spectrometer. The surface footprints of these measurements are categorized ...according to geological terrain. Northern smooth plains deposits and the plains interior to the Caloris basin differ compositionally from older terrain on Mercury. The older terrain generally has higher Mg/Si, S/Si, and Ca/Si ratios, and a lower Al/Si ratio than the smooth plains. Mercury's surface mineralogy is likely dominated by high‐Mg mafic minerals (e.g., enstatite), plagioclase feldspar, and lesser amounts of Ca, Mg, and/or Fe sulfides (e.g., oldhamite). The compositional difference between the volcanic smooth plains and the older terrain reflects different abundances of these minerals and points to the crystallization of the smooth plains from a more chemically evolved magma source. High‐degree partial melts of enstatite chondrite material provide a generally good compositional and mineralogical match for much of the surface of Mercury. An exception is Fe, for which the low surface abundance on Mercury is still higher than that of melts from enstatite chondrites and may indicate an exogenous contribution from meteoroid impacts.
Key Points
Analysis of spatially resolved X‐ray spectrometry data from MESSENGER
Volcanic smooth plains units differ compositionally from older terrains
Mercury's surface consists of high‐Mg mafic minerals, plagioclase, and sulfides
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