^1,2S.J. vanBommel et al. (>10)
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2024.116355]
¹McDonnell Center for the Space Sciences, Washington University in St. Louis, St. Louis, MO, USA
²Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, MO, USA
Copyright Elsevier

The “Planetary Instrument for X-ray Lithochemistry” (PIXL) X-ray spectrometer conducts in situ geochemical analyses of martian rocks and regolith interrogated by the Mars 2020 rover, Perseverance. In addition to quantifying primary rock-forming elements, PIXL can quantify trace elements that in turn can provide additional constraints on the geologic history of Mars. Accurate quantifications of trace elements can require additional analytical techniques to mitigate experimental, background, and crystalline effects within PIXL spectra. In this study, we focus on reducing the impact of these effects and investigate the potential presence of rare earth elements (REEs). The study specifically investigates cerium given its typical relative abundance in many geologic materials compared to other REEs and its potential to mimic fluorescence features produced by organics under deep UV excitation. A detailed analysis of PIXL targets analyzed through the first 887 martian days of the Perseverance mission did not produce any conclusive Ce detections. Phosphorus-enriched materials analyzed by PIXL are estimated to contain sub-675 ppm Ce and sulfate-enriched materials sub-450 ppm Ce. The method presented can help constrain limits on the abundance of additional trace elements of interest that also face a similar analytical burden. PIXL’s potential to assess REE abundances, outside of yttrium, is limited for expected concentrations in surface materials. Determining most REE concentrations in materials interrogated by Perseverance will therefore likely require terrestrial analyses.

^1,2A. G. J. Jurewicz,³A. M. Amarsi,⁴D. S. Burnett,^5,6N. Grevesse
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14272]
¹School of Earth and Space Exploration, Arizona State University Busek Center for Meteorite Studies, Tempe, Arizona, USA
²Department of Earth Science, Dartmouth College, Hanover, New Hampshire, USA
³Theoretical Astrophysics, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden
⁴Department of Geology and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
⁵Centre Spatial de Liège, Université de Liège, Liège, Belgium
⁶STAR Institute, Université de Liège, Liège, Belgium
Published by arrangement with John Wiley & Sons

CI chondrites have been a proxy for the solar system since the mid-20th century. The photospheric and CI chondrite abundances (P and CI, respectively) show a strong correlation. CI as a proxy is also justified by the (i) smoothness of their abundances plotted as a function of odd mass number and (ii) agreement within the error of P as determined spectroscopically. But our statistical assessment of spectroscopic studies and solar wind from the Genesis mission indicates that the small, ~10%–30%, differences (residuals) between CI and P depend on the 50% condensation temperature (Tc50). So, if CI is to be used as a proxy for P, Cosmochemists may want to add a correction to individual elements. Our work is consistent with two published hypotheses: that (i) residuals are linear with Tc50 and (ii) that elements having Tc50 > 1343 K are depleted relative to those with 495 K < Tc50 < 1343 K in CI. We discuss other interpretations which are also feasible. Understanding these small differences of the CI and P for different elements and their variation with Tc50 can help constrain future models of solar system formation and the history of CI chondrites.