¹Kayla Iacovino,²Francis M.McCubbin,³Kathleen E.Vander Kaaden,¹Joanna Clark,⁴Axel Wittmann,¹Ryan S.Jakubek,¹Gordon M.Moore,²Marc D.Fries,¹Doug Archer,²Jeremy W.Boyce
Earth and Planetary Science Letters 602, 117908 Link to Article [https://doi.org/10.1016/j.epsl.2022.117908]
¹ARES, Jacobs/NASA Johnson Space Center, 2101 E NASA Pkwy, Houston, TX 77058 USA
²ARES, NASA Johnson Space Center, 2101 E NASA Pkwy, Houston, TX 77058 USA
³NASA Headquarters, Mary W. Jackson Building, Washington, D.C., 20546 USA
⁴Eyering Materials Center, Arizona State University, 1001 S. McAllister Ave., Tempe, AZ 95287-8301 USA
Copyright Elsevier

Here we present the results of experiments designed to reproduce the interaction between super-solidus mercurian magmas and graphite at high temperatures (ramped up from ambient temperature to 1195–1390 °C) and low pressure (10 mbar). The compositions of resultant gases were measured in situ with a thermal gravimeter/differential scanning calorimeter connected to a mass spectrometer configured to operate under low pressures and reducing conditions. Solid run products were analyzed by electron microprobe and Raman spectroscopy. Three magma starting compositions were based on the composition of the Borealis Planitia region (termed NVP for the Northern Volcanic Plains) on Mercury ± alkali metals, sulfur, and transition metal oxides. Smelting between FeOmelt and graphite was observed above 1100 °C, evidenced by the generation of CO and CO2 gas and the formation of Fe-Si metal alloys, which were found in contact with residual graphite grains. Experiments with transition metal oxide-free starting compositions did not produce metal alloys and showed no significant gas production. In all runs that produced gas, C-O-H±S species dominated the degassing vapor. Our results suggest that the consideration of graphite smelting processes can significantly increase calculated eruption velocities and that gas produced by smelting alone can account for >75% of the pyroclastic deposits identified on Mercury. A combination of S-H-degassing and CO-CO2 production from smelting can explain all but the single largest pyroclastic deposit on Mercury.

^1,2Kainen L.Utt,^1,2Ryan C.Ogliore,^1,2Nan Liu,³Alexander N.Krot,³John P.Bradley,⁴Donald E.Brownlee,⁴David J.Joswiak
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.11.020]
¹Department of Physics, Washington University in St. Louis, St. Louis, MO 63130
²McDonnell Center for the Space Sciences, Washington University in St. Louis, St. Louis, MO 63130
³Hawaii Institute of Geophysics and Planetology, University of Hawaii at Mānoa, Honolulu, HI 96822
⁴Department of Astronomy, University of Washington, Seattle, WA 98195
Copyright Elsevier

Filamentary enstatite crystals, formed by gas-solid condensation in the solar nebula, are found in chondritic porous interplanetary dust particles of probable cometary origin. We measured the oxygen isotopic composition of four filamentary enstatite grains, two whiskers (1.8μm and 2.3μm in length) and two ribbons (3.4μm and 6.1μm in length), from the giant cluster interplanetary dust particle U2-20 GCP using NanoSIMS ion imaging. These grains represent both the ¹⁶O-rich solar (δ^17,18O ≈-70 ‰) and ¹⁶O-poor planetary (δ^17,18O ≈0 ‰) isotope reservoirs. Our measurements provide evidence for very early vaporization of dust-poor and dust-rich regions of the solar nebula, followed by condensation and outward transport of crystalline dust to the comet-forming region very far from the Sun. Similar processes are likely responsible for the crystalline silicates observed in the outer regions of protoplanetary disks elsewhere in the Galaxy.