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Pristine meteoritic materials carry light element isotopic fractionations that constrain physiochemical conditions during solar system formation. Here we report the discovery of a unique xenolith in the metal-rich chondrite Isheyevo. Its fine-grained, highly pristine mineralogy has similarity with interplanetary dust particles (IDPs), but the volume of the xenolith is more than 30,000 times that of a typical IDP. Furthermore, an extreme continuum of N isotopic variation is present in this xenolith: from very light N isotopic composition (delta(15)N(AIR) = -310 +/- 20 per thousand), similar to that inferred for the solar nebula, to the heaviest ratios measured in any solar system material (delta(15)N(AIR) = 4,900 +/- 300 per thousand). At the same time, its hydrogen and carbon isotopic compositions exhibit very little variation. This object poses serious challenges for existing models for the origin of light element isotopic anomalies.

Introduction: Calcium-aluminium-rich inclusions (CAIs), the first solids to have condensed out of the gaseous nebula surrounding the nascent Sun, represent direct witnesses of the processes that set the initial architecture of our solar system. In particular, CAIs preserve evidence that short-lived radionuclides (SLRs; e.g., 10Be, 26Al, 41Ca, 60Fe) with half lives < 5Myr were present during the earliest phases of our solar system's build-up [1]. However, the source(s) of SLRs in the CAI-forming region, as well as the heterogeneous nature of their overall distribution across the solar system, remain highly uncertain. It is unclear whether the occurrence of SLRs in CAIs represent the inheritance of the long-term chemical evolution of the Galaxy, early injection into the solar system by a nearby supernova, and/or traces of early solar irradiation (e.g., [1-4]). These information are yet crucial for understanding the birth environment and formation timescales of the solar system, as well as the nature and extent of early solar irradiation processes. Fossil records of solar irradiation have the potential to inform us about the nature (gradual vs. impulsive flares) and magnitude of the young Sun's activity, the cosmolocation of the CAI factory, and the process(es) accounting for their efficient transport to the outer Solar System [5], where they were accreted into carbonaceous asteroids. Among the SLRs whose former existence in the solar nebula has been demonstrated, 26Al (decays to 26Mg, t1/2 = 0.7 Myr) and 41Ca (decays to 41K, t1/2 = 0.1 Myr) have attracted increasing interest since the proposal of their correlated presence/absence in CV chondrite CAIs and CM chondrite refractory hibonite grains [6-8]. A synchronous decay between 26Al and 41Ca would indeed suggest that the two radionuclides were homogeneously distributed in the solar nebula, and that the Al-Mg and Ca-K systems can be used as chronometers. In 2012, the reanalysis of the Ca-K system with an advanced analytical technique however led to an order of magnitude revision of the initial 41Ca/40Ca in the solar system [9]. Even then, the major interference of (40Ca42Ca)++ at mass 41 could not be resolved under any available mass resolution (M/ΔM = 34,000 is needed) [9]. Recent 41Ca-41K isotopic data acquired for two Type A CAIs from the Vigarano CV3 chondrite using this technique were combined with Al-Mg systematics to suggest that 41Ca distribution was actually not homogeneous when 26Al was widespread at the canonical level [10]. Such a 41Ca heterogeneity could reflect the effect of in-situ charged particle irradiation by the protoSun in the solar nebula. High precision measurements of 41Ca/40Ca in CAIs are clearly needed to shed light on the source(s) of 41Ca in the early solar system, and determine whether or not the Ca-K system constitutes a reliable chronometer for early solar system formation. Research project: We have carried out in-situ 26Al-26Mg and 41Ca-41K analyses in a series of coarse-grained CAIs from the Efremovka (including the well characterized CAI E101.1 [11]), Vigarano, and Allende (CAI 3529-Z [12]) CV3 chondrites, as well as a Forsterite-bearing Type B CAI (from Allende, bulk ?17O = -12‰) exhibiting remarkable internal zoning structures revealed by high-resolution cathodoluminescence imaging. This study takes advantage of the new generation Cameca 1280 HR2 SIMS (Nancy, France) recently equipped with a stable, high-density radio frequency primary ion source. In collaboration with the Cameca firm, we have recently developed new acquisition cards for faraday cups (1012 O) allowing for significantly higher sensitivity and stability during analysis. The unique equipment and design of the CRPG Cameca 1280 HR2 SIMS offers the possibility to perform high mass resolution (= 30,000) measurements enabling, for the first time, resolution of the major interference of (40Ca42Ca)++ at mass 41. We present our most recent analytical developments allowing for high precision 41Ca/40Ca analyses of CAIs, which we interpret in combination with 26Al-26Mg systematics to identify the source(s) of 41Ca in the early solar system. [ABSTRACT FROM AUTHOR]

Short-lived radionuclides (SLRs) are radioactive elements (T1/2 < 200 Myr) which were present in the nascent solar system and are now extinct. While the initial abundance of SLRs with the longest half-lives (T1/2 > 3 Myr) is compatible with the expectations of Galactic evolution models, others have a last-minute origin. 7Be, 10Be, 36Cl, and 41Ca probably originated within the protoplanetary disk from the irradiation of gas and dust by energetic particles accelerated by the protoSun. 26Al and 60Fe were probably synthesized by massive stars and added to interstellar gas which will eventually make up the bulk of our solar system. Identifying the detailed mechanisms of 26Al and 60Fe production and mixing will shed a light on the relationship between the Sun formation history and massive stars. [ABSTRACT FROM AUTHOR]

What have Stardust samples told us about the early solar system? Phil A Bland, Anton T Kearsley, P J Wozniakiewicz, M J Burchell, M Gounelle, M E Zolensky and Matt J Genge have some of the answers – and a few more questions. The Stardust sample-return mission has provided researchers with a glimpse of conditions in the early solar system, in the form of cometary dust with a surprising range of compositions. Some grains arose in the hot inner solar system, others in the cooler outer reaches where comets accrete. There are also grains that formed before the Sun itself. In all, the samples so far have raised as many questions as they have answered, but together they suggest that the early solar system was probably a more complex place than had been supposed. [ABSTRACT FROM AUTHOR]

We present a paleomagnetic study of seven CM carbonaceous chondrites. CM chondrites are believed to be some of the most chemically primitive materials available in our solar system and may sample the continuum of transitional objects between asteroids and comets formed in the outer solar system. As such, CM chondrites can help us to understand primordial aspects of the history of the early solar system including protoplanetary disk and planetesimal magnetism. The ferromagnetic assemblage of CM chondrites is composed of a mixture of primary metallic iron, pyrrhotite, and magnetite. The remanent properties are usually dominated by secondary pyrrhotite. Paleomagnetic analyses using thermal and alternating field demagnetization identified a stable origin-trending component of magnetization in the seven studied CM chondrites. In each meteorite, this component is homogeneous in direction at least at the cm scale and is therefore post-accretional. We interpret this stable component as a pre-terrestrial chemical remanent magnetization acquired during crystallization of magnetite and pyrrhotite during parent body aqueous alteration in a field of at least a few μ T ( 2 ± 1.5 μ T ) . Considering the timescale and intensities of primordial magnetic fields, both internally generated fields from a putative dynamo and external fields, generated in the protoplanetary disk, may have been recorded by CM chondrites. It is presently difficult to discriminate between the two hypotheses. Regardless, CM chondrites likely contain the oldest paleomagnetic record yet identified. [ABSTRACT FROM AUTHOR]

The terrestrial planets and the asteroids dominant in the inner asteroid belt are water poor. However, in the protoplanetary disk the temperature should have decreased below water-condensation level well before the disk was photo-evaporated. Thus, the global water depletion of the inner Solar System is puzzling. We show that, even if the inner disk becomes cold, there cannot be direct condensation of water. This is because the snowline moves towards the Sun more slowly than the gas itself. Thus the gas in the vicinity of the snowline always comes from farther out, where it should have already condensed, and therefore it should be dry. The appearance of ice in a range of heliocentric distances swept by the snowline can only be due to the radial drift of icy particles from the outer disk. However, if a planet with a mass larger than 20 Earth mass is present, the radial drift of particles is interrupted, because such a planet gives the disk a super-Keplerian rotation just outside of its own orbit. From this result, we propose that the precursor of Jupiter achieved this threshold mass when the snowline was still around 3 AU. This effectively fossilized the snowline at that location. In fact, even if it cooled later, the disk inside of Jupiter’s orbit remained ice-depleted because the flow of icy particles from the outer system was intercepted by the planet. This scenario predicts that planetary systems without giant planets should be much more rich in water in their inner regions than our system. We also show that the inner edge of the planetesimal disk at 0.7 AU, required in terrestrial planet formation models to explain the small mass of Mercury and the absence of planets inside of its orbit, could be due to the silicate condensation line, fossilized at the end of the phase of streaming instability that generated the planetesimal seeds. Thus, when the disk cooled, silicate particles started to drift inwards of 0.7 AU without being sublimated, but they could not be accreted by any pre-existing planetesimals. [ABSTRACT FROM AUTHOR]

Primitive interplanetary dust is expected to contain the earliest solar system components, including minerals and organic matter. We have recovered, from central Antarctic snow, ultracarbonaceous micrometeorites whose organic matter contains extreme deuterium (D) excesses (10 to 30 times terrestrial values), extending over hundreds of square micrometers. We identified crystalline minerals embedded in the micrometeorite organic matter, which suggests that this organic matter reservoir could have formed within the solar system itself rather than having direct interstellar heritage. The high D/H ratios, the high organic matter content, and the associated minerals favor an origin from the cold regions of the protoplanetary disk. The masses of the particles range from a few tenths of a microgram to a few micrograms, exceeding by more than an order of magnitude those of the dust fragments from comet 81P/Wild 2 returned by the Stardust mission. [ABSTRACT FROM AUTHOR]