Accretion Region Research Articles

TEMPORARY REMOVAL: Origin of Mars's moons by disruptive partial capture of an asteroid

The origin of Mars’s small moons, Phobos and Deimos, remains unknown. They are typically thought either to be captured asteroids or to have accreted from a debris disk produced by a giant impact. Here, we present an alternative scenario wherein fragments of a tidally disrupted asteroid are captured and evolve into a collisional proto-satellite disk. We simulate the initial disruption and the fragments’ subsequent orbital evolution. We find that tens of percent of an unbound asteroid’s mass can be captured and survive beyond collisional timescales, across a broad range of periapsis distances, speeds, masses, spins, and orientations in the Sun–Mars frame. Furthermore, more than one percent of the asteroid’s mass could evolve to circularise in the moons’ accretion region. This implies a lower mass requirement for the parent body than that for a giant impact, which could increase the likelihood of this route to forming a proto-satellite disk that, unlike direct capture, could also naturally explain the moons’ orbits. These three formation scenarios each imply different properties of Mars’s moons to be tested by upcoming spacecraft missions.

The Ni isotopic composition of Ryugu reveals a common accretion region for carbonaceous chondrites.

The isotopic compositions of samples returned from Cb-type asteroid Ryugu and Ivuna-type (CI) chondrites are distinct from other carbonaceous chondrites, which has led to the suggestion that Ryugu/CI chondrites formed in a different region of the accretion disk, possibly around the orbits of Uranus and Neptune. We show that, like for Fe, Ryugu and CI chondrites also have indistinguishable Ni isotope anomalies, which differ from those of other carbonaceous chondrites. We propose that this unique Fe and Ni isotopic composition reflects different accretion efficiencies of small FeNi metal grains among the carbonaceous chondrite parent bodies. The CI chondrites incorporated these grains more efficiently, possibly because they formed at the end of the disk's lifetime, when planetesimal formation was also triggered by photoevaporation of the disk. Isotopic variations among carbonaceous chondrites may thus reflect fractionation of distinct dust components from a common reservoir, implying CI chondrites/Ryugu may have formed in the same region of the accretion disk as other carbonaceous chondrites.

Hot gas accretion fuels star formation faster than cold accretion in high-redshift galaxies

ABSTRACT We use high-resolution ($\simeq$35pc) hydrodynamical simulations of galaxy formation to investigate the relation between gas accretion and star formation in galaxies hosted by dark matter haloes of mass $10^{12}$${{\mathrm{M}}_{\odot }}$ at $z = 2$. At high-redshift, cold-accreted gas is expected to be readily available for star formation, while gas accreted in a hot mode is expected to require a longer time to cool down before being able to form stars. Contrary to these expectations, we find that the majority of cold-accreted gas takes several hundred Myr longer to form stars than hot-accreted gas after it reaches the inner circumgalactic medium (CGM). Approximately 10 per cent of the cold-accreted gas flows rapidly through the inner CGM on to the galactic disc. The remaining 90 per cent is trapped in a turbulent accretion region that extends up to $\sim 50$ per cent of the virial radius, from which it takes several hundred Myr for the gas to be transported to the star-forming disc. In contrast, most hot shock-heated gas avoids this ‘slow track’, and accretes directly from the CGM on to the disc where stars can form. We find that shock-heating of cold gas after accretion in the inner CGM and supernova-driven outflows contribute to, but do not fully explain, the delay in star formation. These processes combined slow down the delivery of cold-accreted gas to the galactic disc and consequently limit the rate of star formation in Milky Way mass galaxies at $z \gt 2$.

A first systematic characterization of cataclysmic variables in SRG/eROSITA surveys

We present an account of known cataclysmic variables (CVs) that were detected as X-ray sources in eROSITA X-ray surveys and have gai DR3 counterparts. We address standard CVs with main sequence donors and white dwarfs accreting via Roche-lobe overflow (RLOF) and related objects, the double degenerates (DDs), and the symbiotic stars (SySts). We discern between nonmagnetic (dwarf novae and nova-like objects) and magnetic CVs (polars and intermediate polars (IPs)). In the publically available eROSITA catalog from the recent DR1, typically 65<!PCT!> of known cataloged and classified CVs are detected. This fraction rises to over 90<!PCT!> if the stack of all X-ray surveys (called S45 in this paper) is considered and the search volume is restricted to a radius of 500\,pc. We examine the various classes of CVs in various diagnostic diagrams relating X-ray and optical properties (luminosity, absolute magnitude, color, X-ray spectral hardness, and optical variability) and establish their average class properties. We derive spectral properties for the 22 brightest polars and confirm an increase in the ratio of soft to hard X-rays with increasing magnetic field in the accretion region. We report three new soft IPs and present a spectral analysis of all soft IPs. Their blackbody temperatures agree well with published values. The DDs represent the bluest and faintest subcategory but reach the same identification fraction as the standard CVs. The SySts are the most distant systems; only 20 (13<!PCT!>) were detected as X-ray sources in S45, and 7 of those are first-time detections. We investigate their mean properties using an upper limit on the flux of the nondetected CVs. Their X-ray nondetection is indeed a distance effect. We used all properties combined to select candidate CVs for all-sky optical identification programs, with the ultimate aim being to compose large CV samples in order to better constrain the impact of magnetic fields on the evolution of CVs, to derive space densities and luminosity functions, and to quantify the contribution of white-dwarf accreting systems to the Galactic Ridge X-ray emission (GRXE). The results of the optical identification program will be presented in forthcoming papers.

An Eccentric Planet Orbiting the Polar V808 Aurigae

We analyze 15 yr of eclipse timings of the polar V808 Aur. The rapid ingress/egress of the white dwarf and bright accretion region provide timings as precise as a few tenths of a second for rapid cadence photometric data. We find that between 2015 and 2018, the eclipse timings deviated from a linear ephemeris by more than 30 s. The rapid timing change is consistent with the periastron passage of a planet in an eccentric orbit about the polar. The best-fit orbital period is 11 ± 1 yr and we estimate a projected mass of Msin(i)=6.8±0.7 Jupiter masses. We also show that the eclipse timings are correlated with the brightness of the polar with a slope of 1.1 s mag−1. This is likely due to the change in the geometry of the accretion curtains as a function of the mass transfer rate in the polar. While an eccentric planet offers an excellent explanation to the available eclipse data for V808 Aur, proposed planetary systems in other eclipsing polars have often struggled to accurately predict future eclipse timings.

A global 3D simulation of magnetospheric accretion – I. Magnetically disrupted discs and surface accretion

ABSTRACT We present a 3D ideal MHD simulation of magnetospheric accretion on to a non-rotating star. The accretion process unfolds with intricate 3D structures driven by various mechanisms. First, the disc develops filaments at the magnetospheric truncation radius (RT) due to magnetic interchange instability. These filaments penetrate deep into the magnetosphere, form multiple accretion columns, and eventually impact the star at ∼30o from the poles at nearly the free-fall speed. Over 50 per cent (90 per cent) of accretion occurs on just 5 per cent (20 per cent) of the stellar surface. Secondly, the disc region outside RT develops large-scale magnetically dominated bubbles, again due to magnetic interchange instability. These bubbles orbit at a sub-Keplerian speed, persisting for a few orbits while leading to asymmetric mass ejection. The disc outflow is overall weak because of mostly closed field lines. Thirdly, magnetically supported surface accretion regions appear above the disc, resembling a magnetized disc threaded by net vertical fields, a departure from traditional magnetospheric accretion models. Stellar fields are efficiently transported into the disc region due to above instabilities, contrasting with the ‘X-wind’ model. The accretion rate on to the star remains relatively steady with a 23 per cent standard deviation. The periodogram reveals variability occurring at around 0.2 times the Keplerian frequency at RT, linked to the large-scale magnetic bubbles. The ratio of the spin-up torque to $\dot{M}(GM_*R_T)^{1/2}$ is around 0.8. Finally, after scaling the simulation, we investigate planet migration in the inner protoplanetary disc. The disc driven migration is slow in the MHD turbulent disc beyond RT, while aerodynamic drag plays a significant role in migration within RT.

Post-outburst Evolution of Bona Fide FU Ori-type V2493 Cygnus: A Spectro-photometric Monitoring

We present here the results of 8 yr of our near-simultaneous optical–near-infrared spectro-photometric monitoring of the bona fide FU Ori (FUor)-type candidate V2493 Cygnus (V2493 Cyg) starting from 2013 September to 2021 June. During our optical monitoring period (between 2015 October 16 and 2019 December 30), the V2493 Cyg is slowly dimming with an average dimming rate of ∼26.6 ± 5.6 mmag yr−1 in the V band. Our optical photometric colors show a significant reddening of the source post the second outburst pointing toward a gradual expansion of the emitting region post the second outburst. The mid-infrared colors, on the contrary, exhibit a blueing trend, which can be attributed to the brightening of the disk due to the outburst. Our spectroscopic monitoring shows a dramatic variation of the Hα line as it transitioned from absorption feature to the emission feature and back. Such transition can possibly be explained by the variation in the wind structure in combination with accretion. Combining our time evolution spectra of the Ca ii infrared triplet lines with the previously published spectra of V2493 Cyg, we find that the accretion region has stabilized compared to the early days of the outburst. The evolution of the O i λ7773 Å line also points toward the stabilization of the circumstellar disk post the second outburst.

26Al–26Mg chronology of high‐temperature condensate hibonite in a fine‐grained, Ca‐Al‐rich inclusion from reduced CV chondrite

AbstractAl–Mg mineral isochron studies using secondary ion mass spectrometry (SIMS) have revealed the initial 26Al/27Al ratios, (26Al/27Al)0, for individual Ca‐Al‐rich inclusions (CAIs) in meteorites. We find that the relative sensitivity factors of 27Al/24Mg ratio for SIMS analysis of hibonite, one of the major constituent minerals of CAIs, exhibit variations based on their chemical compositions. This underscores the critical need for using appropriate hibonite standards to obtain accurate Al−Mg data. We measured the Al−Mg mineral isochron for hibonite in a fine‐grained CAI (FGI) from the Northwest Africa 8613 reduced CV chondrite by SIMS using synthesized hibonite standards with 27Al/24Mg of ~30, ~100, and ~400. The obtained mineral isochron of hibonite in the FGI yields (26Al/27Al)0 of (4.73 ± 0.09) × 10−5, which is identical to that previously obtained from the mineral isochron of spinel and melilite in the same FGI (Kawasaki et al., 2020). The uncertainties of (26Al/27Al)0 indicate that the constituent minerals in the FGI formed within ~0.02 Myr in the earliest solar system. The disequilibrium O‐isotope distributions of the minerals in the FGI suggest that the O‐isotope compositions of the nebular gas from which they condensed underwent a transitional change from 16O‐rich to 16O‐poor within ~0.02 Myr in the earliest solar system. Once formed, the FGI may have been removed from the forming region within ~0.02 Myr and transported to the accretion region of the parent body.

Complexes of Marginal Sea Paleobasins of the Olyutorka–Kamchatka Region (Structure, Composition and Geodynamics)

The structural features of the Olyutorsko-Kamchatka accretion region allow us to reconstruct two paleobasins for the Late Cretaceous-Paleogene time, separated and fenced off from the ocean by volcanic arcs. The features of the structure and composition of the complexes characterizing the fragments of the oceanic crust show that these basins had a different nature. The age of the fragments of the crust of the Lesnovsko-Iruneisky basin are Alb–Maastrichtian.Volcanites are represented by differentiated toleites of the N-MORB type, rarely intraplate basalts and enriched toleites of E-MORB. Fragments of the crust of the Vetlovsky basin are of age from the Campan–Maastrichtian to the Middle Eocene. Among the volcanites, basalts of N‑MORB are mainly developed, less often E-MORB and, in some structures, basalts of oceanic islands (OIB). Geodynamics in the Late Cretaceous–Cenozoic time for the Kamchatka and Olyutorsky segments differed, starting from the Campanian time.

Serendipitous discovery of the magnetic cataclysmic variable SRGE J075818−612027

We report the discovery of SRGE J075818−612027, a deep stream-eclipsing magnetic cataclysmic variable found serendipitously in SRG/eROSITA calibration and performance verification phase (CalPV) observations of the open cluster NGC 2516 as an unrelated X-ray source. An X-ray timing and spectral analysis of the eROSITA data is presented and supplemented by an analysis of TESS photometry and SALT spectroscopy. X-ray photometry reveals two pronounced dips repeating with a period of 106.144(1) min. The 14-month TESS data reveal the same unique period. A low-resolution identification spectrum obtained with SALT displays hydrogen Balmer emission lines on a fairly blue continuum. The spectrum and the stability of the photometric signal led to the classification of the new object as a polar-type cataclysmic variable. In this context, the dips in the X-ray light curve are explained by absorption in the intervening accretion stream and by a self-eclipse of the main accretion region. The object displays large magnitude differences on long timescales (months) both at optical and X-ray wavelengths, which are interpreted as high and low states and thus support its identification as a polar. The bright phase X-ray spectrum can be reflected with single temperature thermal emission with 9.7 keV and bolometric X-ray luminosity LX ≃ 8 × 1032 erg s−1 at a distance of about 2.7 kpc. The X-ray spectrum lacks the pronounced soft X-ray emission component prominently found in ROSAT-discovered polars.

Confirmation of two magnetic cataclysmic variables as polars: 1RXS J174320.1−042953 and YY Sex

ABSTRACTWe present our analysis of new and archived observations of two candidate magnetic cataclysmic variables, namely 1RXS J174320.1−042953 and YY Sex. 1RXS J174320.1−042953 was observed in two distinctive high and low states where a phase shift was seen, which could be due to changes in the shape, size, and (or) location of the accretion region. We find that its orbital X-ray modulations only persist in the soft (0.3–2.0 keV) energy band, which could be attributed to photoelectric absorption in the accretion flow. The X-ray spectra exhibit a multi-temperature post-shock region where the hard X-rays are absorbed through a thick absorber with an equivalent hydrogen column of ∼7.5 × 1023 cm−2, which partially covers ∼56 per cent of the emission. No soft X-ray excess was found to be present; however, a soft X-ray emission with a blackbody temperature of ∼97 eV describes the spectra. Extensive Transiting Exoplanet Survey Satellite (TESS) observations of YY Sex allow us to refine its orbital period to 1.5746 ± 0.0011 h. We did not find any signature of previously reported spin or beat periods in this system. Furthermore, our new polarimetric observations show clear circular polarization modulated on the orbital period only. Finally, both systems show strong Balmer and He ii 4686 Å emission lines in the optical spectra, further indicative of their magnetic nature.

Oscillations of fluid tori around neutron stars

AbstractWe examine the influence of quadrupole moment of a slowly rotating neutron star (NS) on the oscillations of a fluid accretion disk (torus) orbiting a compact object the spacetime around which is described by the Hartle‐Thorne geometry. Explicit formulae for non‐geodesic orbital epicyclic and precession frequencies, as well as their simplified practical versions that allow for an expeditious application of the universal relations determining the NS properties, are obtained and examined. We demonstrate that the difference in the accretion disk precession frequencies for NSs of the same mass and angular momentum, but different oblateness, can reach up to tens of percent. Even higher differences can arise when NSs with the same mass and rotational frequency, but different equations of state (EoS), are considered. In particular, the Lense‐Thirring precession frequency defined in the innermost parts of the accretion region can differ by more than one order of magnitude across NSs with different EoS. Our results have clear implications for models of the LMXBs variability.

Oxygen isotopes of anhydrous primary minerals show kinship between asteroid Ryugu and comet 81P/Wild2

The extraterrestrial materials returned from asteroid (162173) Ryugu consist predominantly of low-temperature aqueously formed secondary minerals and are chemically and mineralogically similar to CI (Ivuna-type) carbonaceous chondrites. Here, we show that high-temperature anhydrous primary minerals in Ryugu and CI chondrites exhibit a bimodal distribution of oxygen isotopic compositions: 16O-rich (associated with refractory inclusions) and 16O-poor (associated with chondrules). Both the 16O-rich and 16O-poor minerals probably formed in the inner solar protoplanetary disk and were subsequently transported outward. The abundance ratios of the 16O-rich to 16O-poor minerals in Ryugu and CI chondrites are higher than in other carbonaceous chondrite groups but are similar to that of comet 81P/Wild2, suggesting that Ryugu and CI chondrites accreted in the outer Solar System closer to the accretion region of comets.

Hydromorphological management of a lengthy coastal strip in the presence of natural coral reefs flocs in the red sea

Further than the influential role that coral reefs perform in promoting the sustainable development of several diverse aquatic organism species, they may also play a crucially significant environmental role in controlling the hydrodynamic forces and managing the action of sediment movement along wide coastal stretches. This study presents an applied example of a comprehensive hydromorphological investigation focused on the management of sediment transport in the presence of natural coral reefs based on the creation of a numerical model using the Delft3D. A series of model calibrations and verifications demonstrated that the model is capable of replicating the hydrodynamic and sediment transport processes, it is precisely applied to the study of the morphological alteration of the Western Coast of Saudi Arabia, AlWajh & Umluj, Red Sea. Within the model, the natural coral reef flocs were characterized as porous and rough cohesive soil to obtain the maximum possible simulation accuracy and minimize uncertainty. According to the findings, the impacts of remote wind and waves in the midst of coral reefs should be taken into consideration to acquire correct results for monitoring erosion and accretion regions. The results also highlighted how the natural coral reefs effectively inhibit hydrodynamic forces such as waves and ocean currents, which in turn lowered sediment transport activity and led to slight variations in sedimentary stock throughout the one-year simulation.

53Mn‐53Cr chronology and ε54Cr‐Δ17O genealogy of Erg Chech 002: The oldest andesite in the solar system

AbstractThe meteorite Erg Chech (EC) 002 is the oldest felsic igneous rock from the solar system analyzed to date and provides a unique opportunity to study the formation of felsic crusts on differentiated protoplanets immediately after metal–silicate equilibration or core formation. The extinct 53Mn‐53Cr chronometer provides chronological constraints on the formation of EC 002 by applying the isochron approach using chromite, metal–silicate–sulfide, and whole‐rock fractions as well as “leachates” obtained by sequential digestion of a bulk sample. Assuming a chondritic evolution of its parent body, a 53Cr/52Cr model age is also obtained from the chromite fraction. The 53Mn‐53Cr isochron age of 1.73 ± 0.96 Ma (anchored to D'Orbigny angrite) and the chromite model age constrained between and Ma after the formation of calcium‐aluminium‐rich inclusions (CAIs) agree with the 26Al‐26Mg ages (anchored to CAIs) reported in previous studies. This indicates rapid cooling of EC 002 that allowed near‐contemporaneous closure of multiple isotope systems. Additionally, excess in the neutron‐rich 54Cr (nucleosynthetic anomalies) combined with mass‐independent isotope variations of 17O provides genealogical constraints on the accretion region of the EC 002 parent body. The 54Cr and 17O isotope compositions of EC 002 confirm its origin in the “noncarbonaceous” reservoir and overlap with the vestoid material Northwest Africa 12217 and anomalous eucrite Elephant Moraine 92023. This indicates a common feeding zone during accretion in the protoplanetary disk between the source of EC 002 and vestoids. The enigmatic origin of iron meteorites remains still unresolved as EC 002, which is more like a differentiated crust, has an isotope composition that does not match known iron meteorite groups that were once planetesimal cores.

Application of Geospatial Techniques to Determine Coastal Erosion and Accretion along the Ramanathapuram Shore, Tamil Nadu, India

Abstract The coastal region is one of the most sensitive areas on earth. This region has a diversified ecosystem. Erosion and accretion are common natural phenomena that can be seen in this region. In some circumstances, these changes become hazardous to the coastal ecosystem. Natural processes such as rainfall, flood, cyclone, longshore drift, and tectonic shifts can trigger irregular coastal changes. Similarly, anthropogenic factors such as urbanization, unscientific land usage, mining, etc., enhance coastal dynamics and make larger changes. Hence identification of such region has great importance. Geospatial technology has brought various advanced methods for shoreline change studies. It has decreased the huge effort for getting an accurate result for a larger area. Landsat satellite imageries with 30 m spatial resolution have been used for studying the changes in the shoreline of Ramanathapuram for the years 2000, 2005, 2010, 2015 and 2020. In Geographic Information System (GIS) software, the Digital Shoreline Analysis System (DSAS) tool is added for shoreline change analysis. DSAS will build the baseline transects. The rate of shoreline change was calculated using the MATLAB feature runtime function for ArcGIS. Based on the DSAS output, the region of high erosion, low erosion, stable, and low accretion, high accretion zones have been identified on the shore. The results reveal that 5.1% of the shoreline, around 9.3 km is under high erosion, 11.5% of the shoreline, which is around 20.8 km, is under low erosion, 71% of the shoreline, around 128 km, is a stable region, 6.7% of shorelines, around 12 km, have low accretion, and 5.6% of shorelines, around 10.1 km, have high accretion. The coastal villages, namely, Mayakulam, Keelakakrai, Periapattinam, Mandapam, West-Pamban, and East-Rameswaram, have a high erosion with a maximum rate of change between 2.29 to 5.11 m/y. The coastal villages Ervadi, Kalimankund, Sattankonvalsai, South-Pamban and South-Rameswaram have high accretion with a maximum rate of change between 2.34 to 5.24 m/y.

X-ray and optical observations of two AM Her type cataclysmic variables: V388 Peg and V1189 Her

We present time-resolved photometry of a polar V388 Peg and a strong candidate polar V1189 Her observed by T100 telescope at TÜBİTAK National Observatory between June–August 2014 and their X-ray observations using Swift archival data obtained in Apr 2014 (V388 Peg) and in Nov 2011 (V1189 Her). These data were supplemented by archival CRTS, ZTF, ASAS-SN, and ATLAS survey data which show frequent changes between high and low states. This study aims to obtain the temporal behaviors of two systems using the optical light curves and the X-ray spectral properties. The orbital periods of systems are corrected using photometric observations. Results obtained from light curves morphology related to accretion region are discussed for each system. V388 Peg shows a higher amplitude (∼1.6 mag) of orbital modulation and smooth structure in T100 optical observations. It is detected in X-rays at an unabsorbed flux (0.3–10 keV) of 3.6×10−12 erg cm−2 s−1 using a simple model of 30 keV bremsstrahlung model and the model-dependent corresponding luminosity is logL=32.3 erg s−1. The X-ray spectra of V1189 Her is fitted by a bremsstrahlung model and the estimated X-ray luminosity is found to be an order of magnitude lower than the 1032 erg s−1 typical of previously known polars. Using Gaia EDR3 distances, the information obtained from the X-ray spectral analysis and MWD∼0.7M⊙ for both sources, we estimate the mass accretion rates of ∼10−11M⊙ yr−1 (V388 Peg) and ∼10−12M⊙ yr−1 (V1189 Her). As a result of our study, it seems that these two systems have lower mass accretion rates than the long-term accretion rate that is driven by secular evolution, and considering their orbital periods this makes them interesting evolutionary test samples for polars.

Optical Characterization of Two Cataclysmic Variables: RBS 0490 and SDSS J075939.79+191417.3

We present optical photometric and spectroscopic observations of two cataclysmic variables (CVs), namely RBS 0490 and SDSS J075939.79+191417.3. The optical variations of RBS 0490 have been found to occur with a period of 1.689 ± 0.001 hr, which appears to be the probable orbital period of the system. Present photometric observations of SDSS J075939.79+191417.3 confirm and refine the previously determined orbital period as 3.14240928 ± 0.00000096 hr. The presence of long-duration eclipse features in the light curves of SDSS J075939.79+191417.3 indicates that eclipses might be due to an accretion disk and bright spot. The orbital inclination of SDSS J075939.79+191417.3 is estimated to be ∼78° using the eclipse morphology. The phased light-curve variations during the orbital cycle of RBS 0490 provide evidence of emission from an independent second accretion region or a second fainter pole. Optical spectra of RBS 0490 and SDSS J075939.79+191417.3 show the presence of strong Balmer and weak He ii (λ4686) emission lines, along with the detection of strong Hβ emission lines with a large equivalent width. The characteristic features of RBS 0490 seem to favor low-field polars, while SDSS J075939.79+191417.3 appears to be similar to nonmagnetic systems.

Formation of chondrule fine‐grained rims from local nebular reservoirs

AbstractChondrules are commonly surrounded by fine‐grained rims (FGRs) whose origin remains highly debated; both nebular and parent body settings are generally proposed. Deciphering their origin, however, is of fundamental importance as they could clarify the matrix–chondrule relationship and thus constrain the formation and transport conditions of chondrules in the circumsolar disk. Here, we report a systematic survey of FGRs in CO, CM, CV, and CR chondrites; we compare (i) the thickness of FGRs to the size of their host chondrules and (ii) the frequency of FGRs to the modal abundance of matrix in the respective host chondrites. Although FGRs show textural variations depending on the petrologic type of the considered chondrites, our data show a positive correlation between apparent rim thickness and the radius of the host chondrule in all chondrite groups. We also found a positive correlation between the evaluated percentages of rimmed chondrules and the modal abundance of matrix material in the chondrites. We show that this relationship could not result from parent body processes, whether matrix compaction or FGR fragmentation. Therefore, we propose that FGRs were accreted under warm conditions at the end of chondrule‐forming events. Our results thus support (i) a nebular origin for FGR, whose abundances are directly related to the abundance of available dust in regions of chondrite accretion; and (ii) the accretion of chondrites from locally formed chondrules and matrix, suggesting limited radial transport in the protoplanetary disk.

Accretion regions of meteorite parent bodies inferred from a two-endmember isotopic mixing model

ABSTRACT The diverse isotopic anomalies of meteorites demonstrate that the protoplanetary disc was composed of components from different stellar sources, which mixed in the disc and formed the planetary bodies. However, the origin of the accretion materials of different planetary bodies and the cosmochemical relationship between these bodies remain ambiguous. The noncarbonaceous (NC) planetary bodies originate from the inner solar system and have isotopic compositions distinct from those of the carbonaceous (CC) bodies. We combined Ca, Ti, Cr, Fe, Ni, Mo, and Ru isotopic anomalies to develop a quantitative two-endmember mixing model of the NC bodies. Correlations of the isotopic anomalies of different elements with different cosmochemical behaviors originate from the mixing of two common endmembers. Using this mixing model, we calculated the isotopic anomalies of NC bodies for all the considered isotopes, including the isotopic anomalies that are difficult to measure or have been altered by spallation processes. The mixing proportion between the two endmembers in each NC body has been calculated as a cosmochemical parameter, which represents the compositional relationship of the accretion materials between the NC bodies. Using the calculated mixing proportions, the feeding zones of the NC bodies could be estimated. The estimated feeding zones of NC bodies indicate a large population of interlopers in the main asteroid belt and an indigenous origin of Vesta. The feeding zones estimated in different planet formation scenarios indicate that the orbits of Jupiter and Saturn during formation of terrestrial planets were likely to be more circular than their current ones.