Mars does not recycle crustal materials via plate tectonics. For this reason the magmatic water reservoir of the martian mantle has not been affected by surface processes, and the deuterium/hydrogen ...(D/H) ratio of this water should represent the original primordial martian value. Following this logic, hydrous primary igneous minerals on the martian surface should also carry this primordial D/H ratio, assuming no assimilation of martian atmospheric water during crystallization and no major hydrogen fractionation during melt degassing. Hydrous primary igneous minerals, such as apatite and amphibole, are present in martian meteorites here on Earth. Providing these minerals have not been affected by terrestrial weathering, martian atmospheric water, or shock processes after crystallization, they should contain a good approximation of the primordial martian D/H ratio. As Nakhla was seen to fall in the Egyptian desert in 1911, terrestrial contamination is minimized in this meteorite. The nakhlites are also among the least shocked of the martian meteorites. Therefore, apatite within Nakhla could contain primordial martian hydrogen isotope ratios.
We produced in-situ measurements of the D/H ratios in Nakhla apatite grains, using a Cameca ims 1280 ion-microprobe. Our measurements produced D/H values in Nakhla apatite similar to terrestrial values, despite strong evidence that our samples were not significantly contaminated by terrestrial hydrogen. These results suggest that water trapped in the martian mantle has a similar D/H to that of the Earth. Therefore, the water of these two planets may have originated from the same source material. The D/H ratios of the carbonaceous chondrite meteorites, and the Jupiter-family comet 103P/Hartley 2, are similar to the D/H of the two planets, making both these primitive inner solar system materials strong candidates for the source of the terrestrial planets water. These results support recent dynamical models of the formation of the solar system, which suggest material in the inner solar system was homogenized by the migration of Jupiter.
► Nakhla apatite D/H ratios suggest martian mantle has a similar D/H to Earth. ► Possibly indicates water of Earth and Mars originated from the same source. ► Supports recent dynamical models where inner solar system materials are homogenized.
Ratio estimation in SIMS analysis Ogliore, R.C.; Huss, G.R.; Nagashima, K.
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
09/2011, Letnik:
269, Številka:
17
Journal Article
Recenzirano
Odprti dostop
The determination of an isotope ratio by secondary ion mass spectrometry (SIMS) traditionally involves averaging a number of ratios collected over the course of a measurement. We show that this ...method leads to an additive positive bias in the expectation value of the estimated ratio that is approximately equal to the true ratio divided by the counts of the denominator isotope of an individual ratio. This bias does not decrease as the number of ratios used in the average increases. By summing all counts in the numerator isotope, then dividing by the sum of counts in the denominator isotope, the estimated ratio is less biased: the bias is approximately equal to the ratio divided by the summed counts of the denominator isotope over the entire measurement. We propose a third ratio estimator (Beale’s estimator) that can be used when the bias from the summed counts is unacceptably large for the hypothesis being tested. We derive expressions for the variance of these ratio estimators as well as the conditions under which they are normally distributed. Finally, we investigate a SIMS dataset showing the effects of ratio bias, and discuss proper ratio estimation for SIMS analysis.
The Large Hadron–Electron Collider at the HL-LHC Aksakal, H; Alekhin, S; Allport, P P ...
Journal of physics. G, Nuclear and particle physics,
11/2021, Letnik:
48, Številka:
11
Journal Article
From mid-Ordovician ∼470 Myr-old limestone >100 fossil L-chondritic meteorites have been recovered, representing the markedly enhanced flux of meteorites to Earth following the breakup of the ...L-chondrite parent body. Recently one anomalous meteorite, Österplana 065 (Öst 65), was found in the same beds that yield L chondrites. The cosmic-ray exposure age of Öst 65 shows that it may be a fragment of the impactor that broke up the L-chondrite parent body. Here we show that in a chromium versus oxygen-isotope plot Öst 65 falls outside all fields encompassing the known meteorite types. This may be the first documented example of an 'extinct' meteorite, that is, a meteorite type that does not fall on Earth today because its parent body has been consumed by collisions. The meteorites found on Earth today apparently do not give a full representation of the kind of bodies in the asteroid belt ∼500 Myr ago.
Mineralogical observations, chemical and oxygen–isotope compositions, absolute
207Pb–
206Pb ages and short-lived isotope systematics (
7Be–
7Li,
10Be–
10B,
26Al–
26Mg,
36Cl–
36S,
41Ca–
41K,
53Mn–
...53Cr,
60Fe–
60Ni,
182Hf–
182W) of refractory inclusions Ca,Al-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs), chondrules and matrices from primitive (unmetamorphosed) chondrites are reviewed in an attempt to test (i) the
x-wind model
vs. the shock-wave model of the origin of chondritic components and (ii) irradiation
vs. stellar origin of short-lived radionuclides. The data reviewed are consistent with an external, stellar origin for most short-lived radionuclides (
7Be,
10Be, and
36Cl are important exceptions) and a shock-wave model for chondrule formation, and provide a sound basis for early Solar System chronology. They are inconsistent with the
x-wind model for the origin of chondritic components and a local, irradiation origin of
26Al,
41Ca, and
53Mn.
10Be is heterogeneously distributed among CAIs, indicating its formation by local irradiation and precluding its use for the early solar system chronology.
41Ca–
41K, and
60Fe–
60Ni systematics are important for understanding the astrophysical setting of Solar System formation and origin of short-lived radionuclides, but so far have limited implications for the chronology of chondritic components. The chronological significance of oxygen–isotope compositions of chondritic components is limited. The following general picture of formation of chondritic components is inferred. CAIs and AOAs were the first solids formed in the solar nebula ∼4567–4568
Myr ago, possibly within a period of <0.1
Myr, when the Sun was an infalling (class 0) and evolved (class I) protostar. They formed during multiple transient heating events in nebular region(s) with high ambient temperature (at or above condensation temperature of forsterite), either throughout the inner protoplanetary disk (1–4
AU) or in a localized region near the proto-Sun (<0.1
AU), and were subsequently dispersed throughout the disk. Most CAIs and AOAs formed in the presence of an
16O-rich (Δ
17O
∼
−24
±
2‰) nebular gas. The
26Al-poor (
26Al/
27Al)
0
<
1
×
10
−5,
16O-rich (Δ
17O
∼
−24
±
2‰) CAIs – FUN (fractionation and unidentified nuclear effects) CAIs in CV chondrites, platy hibonite crystals (PLACs) in CM chondrites, pyroxene–hibonite spherules in CM and CO chondrites, and the majority of grossite- and hibonite-rich CAIs in CH chondrites—may have formed prior to injection and/or homogenization of
26Al in the early Solar System. A small number of igneous CAIs in ordinary, enstatite and carbonaceous chondrites, and virtually all CAIs in CB chondrites are
16O-depleted (Δ
17O
>
−10‰) and have (
26Al/
27Al)
0 similar to those in chondrules (<1
×
10
−5). These CAIs probably experienced melting during chondrule formation. Chondrules and most of the fine-grained matrix materials in primitive chondrites formed 1–4
Myr after CAIs, when the Sun was a classical (class II) and weak-lined T Tauri star (class III). These chondritic components formed during multiple transient heating events in regions with low ambient temperature (<1000
K) throughout the inner protoplanetary disk in the presence of
16O-poor (Δ
17O
>
−5‰) nebular gas. The majority of chondrules within a chondrite group may have formed over a much shorter period of time (<0.5–1
Myr). Mineralogical and isotopic observations indicate that CAIs were present in the regions where chondrules formed and accreted (1–4
AU), indicating that CAIs were present in the disk as free-floating objects for at least 4
Myr. Many CAIs, however, were largely unaffected by chondrule melting, suggesting that chondrule-forming events experienced by a nebular region could have been small in scale and limited in number. Chondrules and metal grains in CB chondrites formed during a single-stage, highly-energetic event ∼4563
Myr ago, possibly from a gas-melt plume produced by collision between planetary embryos.
Abstract
Porcine epidemic diarrhea virus (PEDV) is a heat-sensitive virus that has devastated the U.S. swine industry. Because of its heat sensitivity, we hypothesized that a steam conditioner and ...pellet mill mimicking traditional commercial thermal processing may mitigate PEDV infectivity. Pelleting, a common feed processing method, includes the use of steam and shear forces, resulting in increased temperature of the processed feed. Two thermal processing experiments were designed to determine if different pellet mill conditioner retention times and temperatures would impact PEDV quantity and infectivity by analysis of quantitative reverse transcription PCR and bioassay. In Exp. 1, a 3 · 3 · 2 factorial design was used with 3 pelleting temperatures (68.3, 79.4, and 90.6°C), 3 conditioning times (45, 90, or 180 s), and 2 doses of viral inoculation (low, 1 · 102 tissue culture infectious dose50 (the concentration used to see cytopathic effect in 50% of the cells)/g, or high, 1 · 104 tissue culture infectious dose50/g). Noninoculated and PEDV-inoculated unprocessed mash were used as controls. The low-dose PEDV–infected mash had 6.8 ± 1.8 cycle threshold (Ct) greater (P < 0.05) PEDV than the high-dose mash. Regardless of time or temperature, pelleting reduced (P < 0.05) the quantity of detectable viral PEDV RNA compared with the PEDV-inoculated unprocessed mash. Fecal swabs from pigs inoculated with the PEDV-positive unprocessed mash, regardless of dose, were clinically PEDV positive from 2 to 7 d (end of the trial) after inoculation. However, if either PEDV dose of inoculated feed was pelleted at any of the 9 tested conditioning time · temperature combinations, no PEDV RNA was detected in fecal swabs or cecum content. Based on Exp. 1 results, a second experiment was developed to determine the impact of lower processing temperatures on PEDV quantity and infectivity. In Exp. 2, PEDV-inoculated feed was pelleted at 1 of 5 conditioning temperatures (37.8, 46.1, 54.4, 62.8, and 71.1°C) for 30 s. The 5 increasing processing temperatures led to feed with respective mean Ct values of 32.5, 34.6, 37.0, 36.5, and 36.7, respectively. All samples had detectable PEDV RNA. However, infectivity was detected by bioassay only in pigs from the 37.8 and 46.1°C conditioning temperatures. Experiment 2 results suggest conditioning and pelleting temperatures above 54.4°C could be effective in reducing the quantity and infectivity of PEDV in swine feed. However, additional research is needed to prevent subsequent recontamination after pelleting as it is a point-in-time mitigation step.
Graphite is one of the many presolar circumstellar condensate species found in primitive meteorites. While the isotopic compositions of low-density graphite grains indicate an origin in core-collapse ...supernovae, some high-density grains have extreme isotopic anomalies in C, Ca, and Ti, which cannot be explained by envelope predictions of asymptotic giant branch (AGB) stars or theoretical supernova models. The Ca and Ti isotopic anomalies, however, match the predictions of He-shell abundances in AGB stars. In this study, we show that the C, Ca, and Ti isotopic anomalies are consistent with nucleosynthesis predictions of the H-ingestion phase during a very late thermal pulse (VLTP) event in post-AGB stars. The low super(12)C/ super(13)C isotopic ratios in these grains are a result of abundant super(12)C efficiently capturing the protons that are being ingested during the VLTP. Very high neutron densities of ~10 super(15) cm super(-3), typical of the i-process, are achieved during this phase in post-AGB stars. The large super(42,43,44)Ca excesses in some graphite grains are indicative of neutron capture nucleosynthesis during VLTP. The comparison of VLTP nucleosynthesis calculations to the graphite data also indicate that apparent anomalies in the Ti isotopic ratios are due to large contributions from super(46,48)Ca which cannot be resolved from the isobars super(46,48)Ti during the measurements. We conclude that presolar graphite grains with moderate to extreme Ca and Ti isotopic anomalies originate in post-AGB stars that suffer a VLTP.
NASA's Genesis Mission returned solar wind (SW) to the Earth for analysis to derive the composition of the solar photosphere from solar material. SW analyses control the precision of the derived ...solar compositions, but their ultimate accuracy is limited by the theoretical or empirical models of fractionation due to SW formation. Mg isotopes are “ground truth” for these models since, except for CAIs, planetary materials have a uniform Mg isotopic composition (within ≤1‰) so any significant isotopic fractionation of SW Mg is primarily that of SW formation and subsequent acceleration through the corona. This study analyzed Mg isotopes in a bulk SW diamond‐like carbon (DLC) film on silicon collector returned by the Genesis Mission. A novel data reduction technique was required to account for variable ion yield and instrumental mass fractionation (IMF) in the DLC. The resulting SW Mg fractionation relative to the DSM‐3 laboratory standard was (−14.4‰, −30.2‰) ± (4.1‰, 5.5‰), where the uncertainty is 2ơ SE of the data combined with a 2.5‰ (total) error in the IMF determination. Two of the SW fractionation models considered generally agreed with our data. Their possible ramifications are discussed for O isotopes based on the CAI nebular composition of McKeegan et al. (2011).
–
We review recent results on O‐ and Mg‐isotope compositions of refractory grains (corundum, hibonite) and calcium, aluminum‐rich inclusions (CAIs) from unequilibrated ordinary and carbonaceous ...chondrites. We show that these refractory objects originated in the presence of nebular gas enriched in 16O to varying degrees relative to the standard mean ocean water value: the Δ17OSMOW value ranges from approximately −16‰ to −35‰, and recorded heterogeneous distribution of 26Al in their formation region: the inferred (26Al/27Al)0 ranges from approximately 6.5 × 10−5 to <2 × 10−6. There is no correlation between O‐ and Mg‐isotope compositions of the refractory objects: 26Al‐rich and 26Al‐poor refractory objects have similar O‐isotope compositions. We suggest that 26Al was injected into the 26Al‐poor collapsing protosolar molecular cloud core, possibly by a wind from a neighboring massive star, and was later homogenized in the protoplanetary disk by radial mixing, possibly at the canonical value of 26Al/27Al ratio (approximately 5 × 10−5). The 26Al‐rich and 26Al‐poor refractory grains and inclusions represent different generations of refractory objects, which formed prior to and during the injection and homogenization of 26Al. Thus, the duration of formation of refractory grains and CAIs cannot be inferred from their 26Al‐26Mg systematics, and the canonical (26Al/27Al)0 does not represent the initial abundance of 26Al in the solar system; instead, it may or may not represent the average abundance of 26Al in the fully formed disk. The latter depends on the formation time of CAIs with the canonical 26Al/27Al ratio relative to the timing of complete delivery of stellar 26Al to the solar system, and the degree of its subsequent homogenization in the disk. The injection of material containing 26Al resulted in no observable changes in O‐isotope composition of the solar system. Instead, the variations in O‐isotope compositions between individual CAIs indicate that O‐isotope composition of the CAI‐forming region varied, because of coexisting of 16O‐rich and 16O‐poor nebular reservoirs (gaseous and/or solid) at the birth of the solar system, or because of rapid changes in the O‐isotope compositions of these reservoirs with time, e.g., due to CO self‐shielding in the disk.
We compare element and isotopic fractionations measured in bulk solar wind samples collected by NASA's Genesis mission with those predicted from models incorporating both the ponderomotive force in ...the chromosphere and conservation of the first adiabatic invariant in the low corona. Generally good agreement is found, suggesting that these factors are consistent with the process of solar wind fractionation. Based on bulk wind measurements, we also consider in more detail the isotopic and elemental abundances of O. We find mild support for an O abundance in the range 8.75-8.83, with a value as low as 8.69 disfavored. A stronger conclusion must await solar wind regime-specific measurements from the Genesis samples.
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