10 research outputs found
Trace Element Abundances in an Unusual Hibonite-Perovskite Refractory Inclusion from Allende
Calcium-aluminum-rich refractory inclusions (CAIs) are thought to be the first-formed solids in the Solar protoplanetary disk and can provide information about the earliest Solar System processes (e.g., [1]). A hibonite-perovskitebearing CAI from the Allende CV3 chondrite (SHAL, [2]) contains a single of 500 micrometers hibonite grain and coarse-grained perovskite. The mineralogy and oxygen isotopic composition of this CAI shows similarities with FUN inclusions, especially HAL [2]. Here we present trace element abundances in SHAL
A review of volatiles in the Martian interior
Multiple observations from missions to Mars have revealed compelling evidence for a volatile-rich Martian crust. A leading theory contends that eruption of basaltic magmas was the ultimate mechanism of transfer of volatiles from the mantle toward the surface after an initial outgassing related to the crystallization of a magma ocean. However, the concentrations of volatile species in ascending magmas and in their mantle source regions are highly uncertain. This work and this special issue of Meteoritics & Planetary Science summarize the key findings of the workshop on Volatiles in the Martian Interior (Nov. 3â4, 2014), the primary open questions related to volatiles in Martian magmas and their source regions, and the suggestions of the community at the workshop to address these open questions
Protracted Timescales for Nebular Processing of First-formed Solids in the Solar System
The calciumâaluminum-rich inclusions (CAIs) from chondritic meteorites are the first solids formed in the solar system. Rim formation around CAIs marks a time period in early solar system history when CAIs existed as free-floating objects and had not yet been incorporated into their chondritic parent bodies. The chronological data on these rims are limited. As seen in the limited number of analyzed inclusions, the rims formed nearly contemporaneously (i.e., <300,000 yr after CAI formation) with the host CAIs. Here we present the relative ages of rims around two type B CAIs from NWA 8323 CV3 (oxidized) carbonaceous chondrite using the ^26 Alâ ^26 Mg chronometer. Our data indicate that these rims formed âŒ2â3 Ma after their host CAIs, most likely as a result of thermal processing in the solar nebula at that time. Our results imply that these CAIs remained as free-floating objects in the solar nebula for this duration. The formation of these rims coincides with the time interval during which the majority of chondrules formed, suggesting that some rims may have formed in transient heating events similar to those that produced most chondrules in the solar nebula. The results reported here additionally bolster recent evidence suggesting that chondritic materials accreted to form chondrite parent bodies later than the early-formed planetary embryos, and after the primary heat source, most likely ^26 Al, had mostly decayed away
Statistical Chronometry of Meteorites. I. The Pb-Pb age of the Solar System's t=0
We use rapidly cooled achondrites to test the assumption of 26Al homogeneity
in the solar nebula, by checking if there is a single value of tSS, the
absolute "Pb-Pb" age of the Solar System's t=0, that makes concordant their
ages from the Al-Mg and Pb-Pb systems. We find that values tSS = 4568.42
+/-0.24 Myr do make these ages concordant, and therefore the hypothesis of
homogeneous 26Al is not falsified. This age, defined to be when the solar
nebula had (26Al/27Al) = 5.23 x 10^-5, is significantly older than the ~4567.3
Myr inferred from direct measurements of Pb-Pb ages in CAIs. Discrepancies
between the Al-Mg and Pb-Pb chronometers in chondrules and CAIs have previously
been interpreted as arising from heterogeneities in 26Al, under the presumption
that the Al-Mg and Pb-Pb systems in CAIs closed simultaneously. We examine this
assumption and show that resetting is to be expected in CAIs. In particular, we
quantitatively demonstrate that it is plausible that Pb-Pb ages of CAIs were
reset at late times, without resetting the earlier Al-Mg ages, if they were
transiently heated in the same manner as chondrules. We critically examine
Pb-Pb isochrons, refining data and suggesting best practices for their
calculation and reporting. We advocate reporting chronometry as times of
formation after t=0 rather than absolute ages, as only the former is useful for
astrophysical models of the solar nebula. We strongly advocate averaging of
multiple samples, rather than anchoring to individual meteorites, to improve
precision.Comment: Accepted by Icaru
Statistical Chronometry of Meteorites. II. Initial Abundances and Homogeneity of Short-lived Radionuclides
Astrophysical models of planet formation require accurate radiometric dating
of meteoritic components by short-lived (Al-Mg, Mn-Cr, Hf-W) and long-lived
(Pb-Pb) chronometers, to develop a timeline of such events in the solar nebula
as formation of Ca-rich, Al-rich Inclusions (CAIs), chondrules, planetesimals,
etc. CAIs formed mostly around a time ("t=0") when the short-lived radionuclide
26Al (t1/2 = 0.72 Myr) was present and presumably homogeneously distributed at
a known level we define as (26Al/27Al)SS = 5.23 x10^-5. The time of formation
after t=0 of another object can be found by determining its initial
(26Al/27Al)0 ratio and comparing it to (26Al/27Al)SS. Dating of meteoritic
objects using the Mn-Cr or Hf-W systems is hindered because the abundances
(53Mn/55Mn)SS and (182Hf/180Hf)SS at t=0 are not known precisely. To constrain
these quantities, we compile literature Al-Mg, Mn-Cr, Hf-W and Pb-Pb data for
14 achondrites and use novel statistical techniques to minimize the
discrepancies between their times of formation across these systems. We find
that for (53Mn/55Mn)SS = (8.09+/-0.65)x10^-6, (182Hf/180Hf)SS =
(10.42+/-0.25)x10^-5, tSS = 4568.36+/-0.20 Myr, and a 53Mn half-life of
3.80+/-0.23 Myr, these four free parameters make concordant 37 formation times
recorded by the different systems in 14 achondrites. These parameters also make
concordant the ages derived for chondrules from CB/CH achondrites, formed
simultaneously in an impact, and are apparently concordant with the I-Xe
chronometer as well. Our findings provide very strong support for homogeneity
of 26Al, 53Mn, and 182Hf in the solar nebula, and our approach offers a
framework for more precise chronometry.Comment: Accepted by Icaru
Abundant presolar grains and primordial organics preserved in carbon-rich exogenous clasts in asteroid Ryugu
Preliminary analyses of asteroid Ryugu samples show kinship to aqueously altered CI (Ivuna-type) chondrites, suggesting similar origins. We report identification of C-rich, particularly primitive clasts in Ryugu samples that contain preserved presolar silicate grains and exceptional abundances of presolar SiC and isotopically anomalous organic matter. The high presolar silicate abundance (104 ppm) indicates that the clast escaped extensive alteration. The 5 to 10 times higher abundances of presolar SiC (~235 ppm), N-rich organic matter, organics with N isotopic anomalies (1.2%), and organics with C isotopic anomalies (0.2%) in the primitive clasts compared to bulk Ryugu suggest that the clasts formed in a unique part of the protoplanetary disk enriched in presolar materials. These clasts likely represent previously unsampled outer solar system material that accreted onto Ryugu after aqueous alteration ceased, consistent with Ryugu's rubble pile origin.ISSN:2375-254
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Abundant presolar grains and primordial organics preserved in carbon-rich exogenous clasts in asteroid Ryugu.
Preliminary analyses of asteroid Ryugu samples show kinship to aqueously altered CI (Ivuna-type) chondrites, suggesting similar origins. We report identification of C-rich, particularly primitive clasts in Ryugu samples that contain preserved presolar silicate grains and exceptional abundances of presolar SiC and isotopically anomalous organic matter. The high presolar silicate abundance (104 ppm) indicates that the clast escaped extensive alteration. The 5 to 10 times higher abundances of presolar SiC (~235 ppm), N-rich organic matter, organics with N isotopic anomalies (1.2%), and organics with C isotopic anomalies (0.2%) in the primitive clasts compared to bulk Ryugu suggest that the clasts formed in a unique part of the protoplanetary disk enriched in presolar materials. These clasts likely represent previously unsampled outer solar system material that accreted onto Ryugu after aqueous alteration ceased, consistent with Ryugus rubble pile origin
Abundant presolar grains and primordial organics preserved in carbon-rich exogenous clasts in asteroid Ryugu
International audiencePreliminary analyses of asteroid Ryugu samples show kinship to aqueously altered CI (Ivuna-type) chondrites, suggesting similar origins. We report identification of C-rich, particularly primitive clasts in Ryugu samples that contain preserved presolar silicate grains and exceptional abundances of presolar SiC and isotopically anomalous organic matter. The high presolar silicate abundance (104 ppm) indicates that the clast escaped extensive alteration. The 5 to 10 times higher abundances of presolar SiC (~235 ppm), N-rich organic matter, organics with N isotopic anomalies (1.2%), and organics with C isotopic anomalies (0.2%) in the primitive clasts compared to bulk Ryugu suggest that the clasts formed in a unique part of the protoplanetary disk enriched in presolar materials. These clasts likely represent previously unsampled outer solar system material that accreted onto Ryugu after aqueous alteration ceased, consistent with Ryuguâs rubble pile origin