Magnetization of carbonaceous asteroids by nebular fields and the origin of CM chondrites

The solar nebula carried a strong magnetic field that had a stable intensity and direction for periods of a thousand years or more1. The solar nebular field may have produced post-accretional magnetization in at least two groups of meteorites, CM and CV chondrites [1–3], which originated from planetesimals that may have underwent aqueous alteration before gas in the solar nebula dissipated [1,3]. Magnetic minerals produced during aqueous alteration, such as magnetite and pyrrhotite [4], could acquire a chemical remanent magnetization from that nebular field [3]. However, many questions about the size, composition, formation time, and, ultimately, identity of the parent bodies that produced magnetized CM and CV chondrites await answers—including whether a parent body might exhibit a detectable magnetic field today. Here, we use thermal evolution models to show that planetesimals that formed between a few Myr after CAIs and ~1 Myr before the nebular gas dissipated could acquire from the nebular field, and retain until today, a chemical remanent magnetization throughout nearly their entire volume. Hence, in-situ magnetometer measurements of C-type asteroids could help link magnetized asteroids to magnetized meteorites. Specifically, a future mission could search for a magnetic field as part of testing the hypothesis that 2 Pallas is the parent body of the CM chondrites [5]. Overall, large carbonaceous asteroids might record ancient magnetic fields in magnetic remanence that produces strong modern magnetic fields, even without a metallic core that once hosted a dynamo.

Tracing the Origins of Refractory Inclusions - the Solar System's Oldest Solids: a Petrographic, Geochemical and 26Al-26Mg Dating Study of CV and CK Refractory Inclusions

<p>Refractory inclusions in carbonaceous chondrite meteorites are of particular interest because both long- and short-lived chronometers have shown that they are the oldest sampled material to have formed in the Solar System. The objective of this study was to establish high-precision petrographic, chemical and isotopic analyses of refractory inclusions and thus offer insights into the chemical and astrophysical environments present during the formation of the Solar System. The former presence of the short-lived isotope 26Al (T1/2 = ca.730 KYr) has been established in a majority of refractory inclusions. Recent studies using both solution-based and in situ methodologies have suggested that the initial 26Al/27Al0 value of refractory inclusions is ca.6 x 10-5, higher than the established "canonical" value of [5.00 +/- 0.05] x 10-5. Knowing the initial concentration of 26Al within the Solar System provides a useful anchor from which ancient materials can be dated. Petrographic and trace element analyses were performed on nine newly-extracted refractory inclusions from CV3 and CK3 chondrites. These analyses revealed all but three refractory inclusions to have experienced multiple episodes of melting and evaporation prior to crystal closure. Mg isotope analyses were performed on eight of the newly extracted refractory inclusions in addition to five inter-laboratory samples. All refractory inclusions shown to have remained unaltered following crystal-closure, regardless of thermal history prior to closure, yielded a model 26Al/27Al0 of [4.89 x 0.265] x 10-5; within error of the canonical value. This result confirms that 26Al was homogenous and at canonical concentrations in the solar nebula. The results also suggest that chemical fractionation and crystal closure for the analysed refractory inclusions was completed within no more than 160 Kyr.</p>

Tracing the Origins of Refractory Inclusions - the Solar System's Oldest Solids: a Petrographic, Geochemical and 26Al-26Mg Dating Study of CV and CK Refractory Inclusions

<p>Refractory inclusions in carbonaceous chondrite meteorites are of particular interest because both long- and short-lived chronometers have shown that they are the oldest sampled material to have formed in the Solar System. The objective of this study was to establish high-precision petrographic, chemical and isotopic analyses of refractory inclusions and thus offer insights into the chemical and astrophysical environments present during the formation of the Solar System. The former presence of the short-lived isotope 26Al (T1/2 = ca.730 KYr) has been established in a majority of refractory inclusions. Recent studies using both solution-based and in situ methodologies have suggested that the initial 26Al/27Al0 value of refractory inclusions is ca.6 x 10-5, higher than the established "canonical" value of [5.00 +/- 0.05] x 10-5. Knowing the initial concentration of 26Al within the Solar System provides a useful anchor from which ancient materials can be dated. Petrographic and trace element analyses were performed on nine newly-extracted refractory inclusions from CV3 and CK3 chondrites. These analyses revealed all but three refractory inclusions to have experienced multiple episodes of melting and evaporation prior to crystal closure. Mg isotope analyses were performed on eight of the newly extracted refractory inclusions in addition to five inter-laboratory samples. All refractory inclusions shown to have remained unaltered following crystal-closure, regardless of thermal history prior to closure, yielded a model 26Al/27Al0 of [4.89 x 0.265] x 10-5; within error of the canonical value. This result confirms that 26Al was homogenous and at canonical concentrations in the solar nebula. The results also suggest that chemical fractionation and crystal closure for the analysed refractory inclusions was completed within no more than 160 Kyr.</p>

Formation conditions of Titan

&lt;p&gt;Satellites are generally believed to form in circumplanetary disks (CPDs): a gas disk containing icy and rocky particles that accumulate to form massive moons over time. The discoveries by the Cassini-Huygens mission have led to a revision of the birth environment of the Saturnian system.&lt;/p&gt; &lt;p&gt;We aim to constrain the formation circumstances of Titan's building blocks by considering the moon's observed characteristics. We use radiation thermo-chemical CPD models and evaluate them on their capacity to reproduce a Titan-like satellite.&lt;/p&gt; &lt;p&gt;To form a moon with Titan's ice-to-rock ratio, we find that the dust-to-gas ratio in the CPD must be in the order of solar nebula values, O(10&lt;sup&gt;-2&lt;/sup&gt;). The ice availability upon accretion is otherwise incompatible with Titan's moment of inertia. Our models predict a large NH&lt;sub&gt;3&lt;/sub&gt; inventory was available upon Titan's formation, &amp;#8764;10-20wt.% of the total ice. This is consistent with the hypothesis that the observed N&lt;sub&gt;2&lt;/sub&gt; in Titan is captured as NH&lt;sub&gt;3&lt;/sub&gt; and converted by photolysis and shock heating, and is compatible with the possible presence of a conductive layer at 45&amp;#177;15 km as revealed by the Huygens probe.&lt;/p&gt;

Strong isotope effect in the VUV photodissociation of HOD: A possible origin of D/H isotope heterogeneity in the solar nebula

The deuterium versus hydrogen (D/H) isotopic ratios are important to understand the source of water on Earth and other terrestrial planets. However, the determinations of D/H ratios suggest a hydrogen isotopic diversity in the planetary objects of the solar system. Photochemistry has been suggested as one source of this isotope heterogeneity. Here, we have revealed the photodissociation features of the water isotopologue (HOD) at λ = 120.8 to 121.7 nm. The results show different quantum state populations of OH and OD fragments from HOD photodissociation, suggesting strong isotope effect. The branching ratios of H + OD and D + OH channels display large isotopic fractionation, with ratios of 0.70 ± 0.10 at 121.08 nm and 0.49 ± 0.10 at 121.6 nm. Because water is abundant in the solar nebula, photodissociation of HOD should be an alternative source of the D/H isotope heterogeneity. This isotope effect must be considered in the photochemical models.

Exploring the link between molecular cloud ices and chondritic organic matter in laboratory

Carbonaceous meteorites are fragments of asteroids rich in organic material. In the forming solar nebula, parent bodies may have accreted organic materials resulting from the evolution of icy grains observed in dense molecular clouds. The major issues of this scenario are the secondary processes having occurred on asteroids, which may have modified the accreted matter. Here, we explore the evolution of organic analogs of protostellar/protoplanetary disk material once accreted and submitted to aqueous alteration at 150 °C. The evolution of molecular compounds during up to 100 days is monitored by high resolution mass spectrometry. We report significant evolution of the molecular families, with the decreases of H/C and N/C ratios. We find that the post-aqueous products share compositional similarities with the soluble organic matter of the Murchison meteorite. These results give a comprehensive scenario of the possible link between carbonaceous meteorites and ices of dense molecular clouds.