¹D.S. Vogt, ¹K. Rammelkamp, ¹S. Schröder, ^1,2H.W. Hübers
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2017.12.006]
¹Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institute of Optical Sensor Systems, Berlin, Germany
²Humboldt-Universität zu Berlin, Department of Physics, Berlin, Germany
Copyright Elsevier

The intensity of the molecular CaCl emission in LIBS spectra is examined in order to evaluate its suitability for the detection of chlorine in a Martian environment. Various mixtures resembling Martian targets with varying Cl content are investigated under simulated Martian conditions. The reactions leading to the formation of CaCl are modeled based on reaction kinetics and are used to fit the measured CaCl band intensities. MgCl bands are also investigated as potential alternatives to CaCl, but no MgCl bands can be identified in samples containing both Mg and Cl. The study confirms that CaCl is well suited for the indirect detection of chlorine, but finds a strong dependence on the concentrations of Ca and Cl in the sample. Spectra from samples with a high chlorine concentration can have low-intensity CaCl emission due to a deficiency of Ca. A qualitative estimate of the sample composition is possible based on the ratio of the band intensity of CaCl to the intensity of Ca emission lines. Time-resolved measurements show that the CaCl concentration in the plasma is highest after about 1 µs.

¹Zoe A. Landsman, ²Joshua P. Emery, ¹Humberto Campins, ³Josef Hanuš, ⁴Lucy F. Lim, ⁵Dale P. Cruikshank
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2017.11.035]
¹Department of Physics, University of Central Florida, 4111 Libra Drive, PS 430, Orlando, FL, 32826, United States
²Earth and Planetary Science Department, Planetary Geosciences Institute, University of Tennessee, 306 EPS Building, 1412 Circle Dr, Knoxville, TN, 37996, United States
³Astronomical Institute, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, Prague, 18000, Czech Republic
⁴NASA Goddard Space Flight Center, Mail Code 691, Greenbelt, MD, 20771, United States
⁵NASA Ames Research Center, Mail Stop 245-6, Moffett Field, CA, 94035, United States
Copyright Elsevier

Asteroid (16) Psyche is a unique, metal-rich object belonging to the “M” taxonomic class. It may be a remnant protoplanet that has been stripped of most silicates by a hit-and-run collision. Because Psyche offers insight into the planetary formation process, it is the target of NASA’s Psyche mission, set to launch in 2023. In order to constrain Psyche’s surface properties, we have carried out a mid-infrared (5–14 μm) spectroscopic study using data collected with the Spitzer Space Telescope’s Infrared Spectrograph. Our study includes two observations covering different rotational phases. Using thermophysical modeling, we find that Psyche’s surface is smooth and likely has a thermal inertia Γ = 5–25 J/m2/K/s1/2 and bolometric emissivity ϵ= 0.9, although a scenario with ϵ=0.7 and thermal inertia up to 95 J/m2/K/s1/2 is possible if Psyche is somewhat larger than previously determined. The smooth surface is consistent with the presence of a metallic bedrock, which would be more ductile than silicate bedrock, and thus may not readily form boulders upon impact events. From comparisons with laboratory spectra of silicate and meteorite powders, Psyche’s 7–14μm emissivity spectrum is consistent with the presence of fine-grained ( < 75μm) silicates on Psyche’s surface. We conclude that Psyche is likely covered in a fine silicate regolith, which may also contain iron grains, overlying an iron-rich bedrock.