^1,2Samuel P. Alpert,^1,2Denton S. Ebel,^1,2,3Michael K. Weisberg,
^1,4Jeremy R. Neiman
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13619]
¹Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York, 10024 USA
²Department of Earth and Environmental Sciences, CUNY Graduate Center, New York, New York, 10016 USA
³Department of Physical Sciences, Kingsborough Community College, CUNY, Brooklyn, New York, 11235 USA
⁴Python developer and participant in the American Museum of Natural History “Hack the Solar System” 2019 Hackathon.
Published by arrangement with John Wiley & Sons

Opaque assemblages (OAs) are small (submillimeter) objects composed primarily of metals, sulfides, and oxides that exist in nearly all chondritic meteorite groups as discrete objects in the matrix or associated with chondrules. The size, morphology, and petrology of OAs vary greatly between different chondrite groups, with petrologic grade within a single group, and by their apparent textural setting. Two hypotheses may explain the formation of matrix OAs: (1) they were separated from chondrules via surface tension during heating events, or (2) they formed as free‐floating objects in the solar nebula; however, this is the first comprehensive study of the petrology of OAs in ordinary chondrites (OCs) as a group, which seeks to determine if one hypothesis is sufficient to explain all such objects. Here, we use a newly developed machine learning algorithm to show that all OAs from the least equilibrated OC, Semarkona (LL 3.01), are composed of kamacite, taenite, troilite, pentlandite, magnetite, and other minor phases. These OAs form two distinct groups based on their modal mineralogy: one group in and associated with chondrules, and the other group free‐floating in the matrix. Chondrule OAs exhibit a bimodal distribution between sulfide‐ and metal‐rich endmembers in agreement with previous findings. Matrix OAs cluster at roughly equal abundances of sulfides and metals and universally exhibit magnetite rims. The two populations of chondrule OAs cannot be combined to form the modal mineralogies observed in matrix OAs and some matrix OAs exhibit mineralogical layering consistent with fractional condensation. Both observations support the hypothesis that matrix OAs were not formed by expulsion from chondrules and instead formed as free‐floating objects in the solar nebula; however, chondrule OAs must have formed with their host chondrules during heating events.

¹Stefan Loehle,¹Martin Eberhart,¹Fabian Zander,¹Arne Meindl,²Regina Rudawska,²Detlef Koschny,²Joe Zender,³Ron Dantowitz,⁴Peter Jenniskens
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13622]
¹Institut für Raumfahrtsysteme, Universität Stuttgart, Stuttgart, 70569 Germany
²ESA ESTEC, Noordwijk, 2201 The Netherlands
³Dexter Southfield, Boston, MA02445 Massachusetts, USA
⁴SETI Institute, Mountain View, CA94043 California, USA
Published by arrangement with John Wiley & Sons

The advancement in the acquisition of spectral data from meteors, as well as the capability to analyze meteoritic entries in ground testing facilities, requires the assessment of the performance of software tools for the simulation of spectra for different species. The Plasma Radiation Database, PARADE, is a line‐by‐line emission calculation tool. This article presents the extensions implemented for the simulation of meteor entries with the additional atomic species Na, K, Ti, V, Cr, Mn, Fe, Ca, Ni, Co, Mg, Si, and Li. These atoms are simulated and compared to ground testing spectra and to observed spectra from the CILBO observatory. The diatomic molecules AlO and TiO have now been added to the PARADE database. The molecule implementations have been compared to the results of a simple analytical program designed to approximate the vibrational band emission of diatomic molecules. AlO and TiO have been identified during the airborne observation campaigns of re‐entering man‐made objects WT1190F and CYGNUS OA6. Comparisons are provided showing reasonable agreement between observation and simulation.