¹M. V. GORYUNOV,²G. VARGA,²Z. DANKHAZI,³I. FELNER,¹A. V. CHUKIN,⁴E. KUZMANN,⁴Z. HOMONNAY,¹V. I. GROKHOVSKY,¹M. I. OSHTRAKH
Meteoritics & Planetary Science (in Press) Link to Article [doi: 10.1111/maps.13984]
¹Institute of Physics and Technology, Ural Federal University, Ekaterinburg, Russian Federation
²Department of Materials Physics, Eotvos Lorand University, Budapest, Hungary
³Racah Institute of Physics, The Hebrew University, Jerusalem, Israel
⁴Laboratory of Nuclear Chemistry, Institute of Chemistry, Eotvos Lorand University, Budapest, Hungary
Published by arrangement with John Wiley & Sons

Gibeon IVA iron meteorite fragment was characterized using optical microscopy,scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), X-raydiffraction (XRD), magnetization measurements, and M€ossbauer spectroscopy. Opticalmicroscopy and SEM made on the polished section of the meteorite, show the presence ofa-Fe(Ni, Co) andc-Fe(Ni, Co) phases and plessite structures. There are no troilite inclusionsobserved in the studied section. EDS studies indicate some variations in the Ni concentrations:(i) within thea-Fe(Ni, Co) phase in the range~5.00.1–~7.50.1 at% and (ii) within thec-Fe(Ni, Co) phase in the range~26.00.2–~36.10.2 at%. The latter Ni concentrationrange indicates the presence of small amount of the paramagneticc-phase in addition to theferromagneticc-phase. EDS also shows that Ni content in two plessite structures is varying inthe range~16–37 at%, which can indicate the presence of only thea2-Fe(Ni, Co) andc-Fe(Ni,Co) phases in the duplex plessite structure. This may be a result of thec-phase decompositionwith the incomplete martensitic transformation:c?a2+cdue to a faster cooling rate. XRDindicates the presence of~1.3 wt% of thec-Fe(Ni, Co) phase in Gibeon VIA. The saturationmagnetization moment of 185(2) emu g1obtained also confirms the presence of phases withlow and high Ni concentrations. The most appropriate fit of the Gibeon IVA M€ossbauerspectrum demonstrates the presence of five magnetic sextets and one paramagnetic singlet whichare assigned to the ferromagnetica2-Fe(Ni, Co),a-Fe(Ni, Co),c-Fe(Ni, Co), and paramagneticc-Fe(Ni, Co) phases. The relative average Fe contents in these phases are: 13.4% in thea2-Fe(Ni, Co) phase, 78.3% in thea-Fe(Ni, Co) phase, and 8.3% in the ferromagnetic andparamagneticc-Fe(Ni, Co) phases.

^1,2,3,4Sarah McMullan et al. (>10)
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13977]
¹Impact and Astromaterials Research Centre, Department of Earth Science and Engineering, Imperial College London, SW7 2BP London, UK
²UK Fireball Network (UKFN), UK
³UK Fireball Alliance (UKFAll), UK
⁴Global Fireball Observatory (GFO), Australia
Published by arrangement with John Wiley & Sons

On February 28, 2021, a fireball dropped ∼0.6 kg of recovered CM2 carbonaceous chondrite meteorites in South-West England near the town of Winchcombe. We reconstruct the fireball’s atmospheric trajectory, light curve, fragmentation behavior, and pre-atmospheric orbit from optical records contributed by five networks. The progenitor meteoroid was three orders of magnitude less massive (∼13 kg) than any previously observed carbonaceous fall. The Winchcombe meteorite survived entry because it was exposed to a very low peak atmospheric dynamic pressure (∼0.6 MPa) due to a fortuitous combination of entry parameters, notably low velocity (13.9 km s−1). A near-catastrophic fragmentation at ∼0.07 MPa points to the body’s fragility. Low entry speeds which cause low peak dynamic pressures are likely necessary conditions for a small carbonaceous meteoroid to survive atmospheric entry, strongly constraining the radiant direction to the general antapex direction. Orbital integrations show that the meteoroid was injected into the near-Earth region ∼0.08 Myr ago and it never had a perihelion distance smaller than ∼0.7 AU, while other CM2 meteorites with known orbits approached the Sun closer (∼0.5 AU) and were heated to at least 100 K higher temperatures.