¹F.J.M. Rietmeijer, ²V. Della Corte, ²M. Ferrari, ^2,3A. Rotundi, ⁴R. Brunetto
¹Department of Earth and Planetary Sciences, MSC03 2040, 1-University of New Mexico, Albuquerque, NM 87131-0001, USA
²Istituto di Astrofisica e Planetologia Spaziali – INAF, Via del Fosso del Cavaliere, 100, 00133, Roma, Italy
³Dipartimento di Scienze Applicate, Università degli Studi di Napoli “Parthenope”, CDN, I C4, 80143, Napoli, Italy
⁴Institut d’Astrophysique Spatiale, CNRS, UMR-8617, Université Paris-Sud, bâtiment 121, F-91405 Orsay Cedex, France

Bolide and fireball fragmentation produce vast amounts of dust that will slowly fall through the stratosphere. DUSTER (Dust in the Upper Stratosphere Tracking Experiment and Retrieval) was designed to intercept the nanometer to micrometer meteoric dust from these events for laboratory analyses while it is still in the upper stratosphere. This effort required extraordinary precautions to avoid particle contamination during collection and in the laboratory. Here we report dust from the upper stratosphere that was collected during two campaigns one in 2008 and another in 2011. We collected and characterized forty five uncontaminated meteoric dust particles. The collected particles are alumina, aluminosilica, plagioclase, fassaite, silica, CaCO3, CaO, extreme F-rich C-O-Ca particles, and oxocarbon particles. These particles are found in friable CI and CM carbonaceous chondrite, and unequilibrated ordinary chondrite meteoroids that are the most common source of bolides and fireballs. The oxocarbons have no meteorite counterparts. Some F-bearing CaCO3 particles changed shape when they interacted with the ambient laboratory atmosphere which might indicate their highly unequilibrated state as a result of fragmentation. Equilibrium considerations constrain the thermal regime experienced by the collected particles between ∼2000°C and ∼1000°C, as high as 3,700°C and as low as ∼650°C after 9 secs, followed by rapid quenching (μs) to below 1,600°C, but equilibrium conditions during these events is most unlikely. So far the observed thermal conditions in these events put the temperatures between ∼4,300°C and ∼430°C for 5 seconds and high cooling rates. Such conditions are present in the immediate wake of meteors and fireballs.

Reference
Rietmeijer FJM, Della Corte V, Ferrari M, Rotundi A, Brunetto R (2015) Laboratory Analyses of Meteoric Debris in the Upper stratosphere from Settling Bolide Dust Clouds. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.11.003]
Copyright Elsevier

¹Breanne L. Berg, ¹Edward A. Cloutis, ²Pierre Beck, ³Pierre Vernazza, ⁴Janice L. Bishop, ⁵Driss Takir, ⁶Vishnu Reddy, ¹Daniel Applin, ¹Paul Mann
¹Department of Geography, University of Winnipeg, Winnipeg, MB, Canada R3B 2E9
²Université de Grenoble Alpes, IPAG, F-38000 Grenoble, France
³Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
⁴SETI Institute, 89 Bernardo Ave, Suite 100, Mountain View, CA, USA 94043
⁵Astrogeology Science Center, United States Geological Survey, 2255 N. Gemini Dr., Flagstaff, AZ, 86001, USA
⁶Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ, USA 85719-2395

Ammonium-bearing minerals have been suggested to be present on Mars, Ceres, and various asteroids and comets. We undertook a systematic study of the spectral reflectance properties of ammonium-bearing minerals and compounds that have possible planetary relevance (i.e., ammonium carbonates, chlorides, nitrates, oxalates, phosphates, silicates, and sulfates). Various synthetic and natural NH4+-bearing minerals were analyzed using reflectance spectroscopy in the long-wave ultraviolet, visible, near-infrared, and mid-infrared regions (0.35-8 μm) in order to identify spectral features characteristic of the NH4+ molecule, and to evaluate if and how these features vary among different species. Mineral phases were confirmed through structural and compositional analyses using X-ray diffraction, X-ray fluorescence, and elemental combustion analysis. Characteristic absorption features associated with NH4 can be seen in the reflectance spectra at wavelengths as short as ∼1 μm. In the near-infrared region, the most prominent absorption bands are located near 1.6, 2.0, and 2.2 μm. Absorption features characteristic of NH4+ occurred at slightly longer wavelengths in the mineral-bound NH4+ spectra than for free NH4+ for most of the samples. Differences in wavelength position are attributable to various factors, including differences in the type and polarizability of the anion(s) attached to the NH4+, degree and type of hydrogen bonding, molecule symmetry, and cation substitutions. Multiple absorption features, usually three absorption bands, in the mid-infrared region between ∼2.8 and 3.8 μm were seen in all but the most NH4-poor sample spectra, and are attributed to fundamentals, combinations, and overtones of stretching and bending vibrations of the NH4+ molecule. These features appear even in reflectance spectra of water-rich samples which exhibit a strong 3 μm region water absorption feature. While many of the samples examined in this study have NH4 absorption bands at unique wavelength positions, in order to discriminate between different NH4+-bearing phases, absorption features corresponding to molecules other than NH4+ should be included in spectral analysis. A qualitative comparison of the laboratory results to telescopic spectra of asteroids 1 Ceres, 10 Hygiea, and 324 Bamberga for the 3 μm region demonstrates that a number of NH4-bearing phases are consistent with the observational data in terms of exhibiting an absorption band in the 3.07 μm region.

Reference
Berg BL, Cloutis EA, Beck P, Vernazza P, Bishop JL, Takir D, Reddy V, Applin D, Mann P (2015) Reflectance spectroscopy (0.35-8 μm) of ammonium-bearing minerals and qualitative comparison to Ceres-like asteroids. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.10.028]
Copyright Elsevier