¹Tabea Bogdan, ¹Jens Teiser, ¹Nikolai Fischer, ¹Maximilian Kruss, ¹Gerhard Wurm
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.09.011]
University of Duisburg-Essen, Faculty of Physics, Lotharstr. 1-21, Duisburg, 47057, Germany
Copyright Elsevier

In laboratory experiments, spherical 1-mm-wide glass and basalt particles are heated, and the hot particles collide at about 1 m/s with a flat glass target that is at room temperature. When the particles are heated below 900 K, the collisions are essentially elastic with coefficients of restitution of about 0.9, but above 900 K collisions become increasingly inelastic and the coefficient of restitution decreases with increasing temperature. At 1100 K the glass particles approach sticking but, simultaneously, at the same temperature the particles melt on timescales of minutes. The basalt particles approach sticking at 1200 K. Only above 1400 K do basalt grains in contact with each other fuse together, forming compounds on timescales of hours, and at 1500 K basalt grains completely fuse together. Therefore, cooling basalt grains only have a 100 K window for compound formation, and velocities very likely have to be below 1 m/s for sticking in the first place. We predict that this puts constraints on compound chondrule formation and particle densities in the solar nebula.

^1,2M.S.Thompson, ^3,4M.J.Loeffler, ¹R.V.Morris, ¹L.P.Keller, ⁵R.Christoffersen
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.09.022]
¹ARES, NASA Johnson Space Center, Houston, TX 77058
²Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN 47907
³NASA Goddard Space Flight Center, Greenbelt, MD 20771
⁴Northern Arizona University, Department of Physics and Astronomy, Flagstaff, AZ 86011
⁵Jacobs, NASA Johnson Space Center, Mail Code XI3, Houston, TX
Copyright Elsevier

We performed pulsed-laser irradiation of a chip of the CM2 Murchison carbonaceous chondrite meteorite to simulate micrometeorite impacts on carbonaceous asteroids. Optical reflectance spectroscopy and by transmission electron microscopy were performed to characterize the unirradiated and irradiated samples and vapor and melt deposits collected on a glass slide ∼7 mm from the surface of the sample. The spectrum of the deposit on the glass slide shows a red slope between 0.35-2.5 µm, while the irradiated surface of the meteorite shows only slight darkening over the same spectral range. We identified predominant melt products and vesiculated textures in the glass slide deposit, in the fine-grained matrix of the meteorite, and in individual mineral phases of the meteorite chip. Extracted focused ion beam (FIB) sections from the matrix material, an olivine grain, a pentlandite grain, and from the glass slide deposit were analyzed by scanning transmission electron microscopy (STEM). Microstructural and chemical analyses based on the STEM observations show widespread melting and the formation of Fe-bearing nanoparticles (including prevalent Fe-Ni-sulfides) across the surface of the meteorite. The section extracted from the glass slide revealed nanoparticles embedded in a chemically and microstructurally complex deposit, which likely formed as a result of both melting and vaporization processes. These analyses reveal a significantly more compositionally diverse population of nanoparticles compared to what is observed in lunar or ordinary chondritic space weathered samples. We discuss the implications these results have for the space weathering of carbonaceous asteroids and their importance for understanding the surface processes on primitive bodies.