Project:	Enhancing the elemental calibration of the PIXL X-ray fluorescence spectrometer on the Mars 2020 Perseverance Rover (JPL AO No. 16117)
Disciplines:	Geochemistry, Instrument calibration
Mentor:	Chris Heirwegh, (JPL), christopher.m.heirwegh@jpl.nasa.gov, Phone: (626) 807-5420
Mentor URL:	https://science.jpl.nasa.gov/people/heirwegh/  (opens in new window)
Background:	The Planetary Instrument for X-ray Lithochemistry (PIXL) [1] is a focused beam in situ X-ray fluorescence (XRF) spectrometer mounted on the arm of the National Aeronautics and Space Administration (NASA)’s Mars 2020 Perseverance Rover. Planetary scientists rely on PIXL’s quantifiable elemental map-making capability to resolve details of chemical textures in the rock. Data returned to Earth from PIXL support the search for answers to questions on the early formation of Mars, conditions for past habitability and signs of possible biosignatures found in the rock record. Prior to launch PIXL underwent a calibration procedure to enable its elemental analysis capabilities and generate uncertainty tolerances for each element [2]. Due to the limited number of geological reference materials (GRMs) used in the calibration, many elements were grouped under a single uncertainty value rather than on a per-element basis. As well, the calibration did not rigorously assess quantification limits of certain trace elements like Ce, whose substitution in crystals defects complicates organic detections in aqueously altered rocks [3,4]. New XRF measurements on numerous additional GRMs are needed to extend the calibration so that individual per-element uncertainties can be refined and quantification limits for trace elements can be better understood. Since the PIXL flight hardware is no longer accessible, data recorded on the PIXL-like breadboard spectrometer (Pbs) [5], located at JPL, are expected to provide trends that are both similar and traceable to the flight unit. Mars 2020 scientists at JPL are attempting to answer the question, “can PIXL’s calibration be refined to improve knowledge of uncertainties and detectability through measurements of many additional reference materials on JPL’s ground-based analogue PIXL (breadboard) testbed?” The efforts undertook by the candidate accepted to this position are expected to provide new calibration data to upgrade the PIXL data processing pipeline and will therefore directly benefit the Mars scientific community in their ongoing analysis of PIXL data.
Description:	The selected candidate will measure several dozen existing pressed powder and glass GRMs using the Pbs. These are largely the same sample set as were used to assess uncertainties for the Alpha-Particle X-ray Spectrometer (APXS) on board NASA’s Curiosity Rover [6]. The candidate will then process the data using the PIXL Quantitative XRF software (PIQUANT) [5,7] to derive elemental composition information and compare these to reference values for each material. Pre-existing reference data sheets will be utilized to supply compositional information for each material. Pbs data will also be recorded using the same calibration target set as used to calibrate the PIXL flight hardware. That way, any trends or differences between flight and Pbs systems will be traceable. The candidate will derive per-element uncertainty values for the Pbs and use the traceability trends to infer accuracy of the flight hardware. Derivation of uncertainties and quantification limits for relevant trace elements, including Ce and several others, will also be derived. The selected candidate will work closely with Dr. Chris Heirwegh, provide weekly updates on their progress and a final written report summarizing their work and findings. The outcome of this work for the candidate is that they will gain experience in an exercise to calibrate a space-flight instrument and, participate in a calibration – research effort that may lead to interaction with the PIXL science team and co-authorship on a publication.
References:	[1] A. C. Allwood et al., PIXL: Planetary Instrument for X-ray Lithochemistry, Space Sci. Rev. 216 (2020) 134. doi:https://doi.org/10.1007/s11214-020-00767-7 [2] C. M. Heirwegh et al., Pre-Flight Calibration of PIXL for X-ray Fluorescence Elemental Quantification (2024) arXiv:2402.01544 [physics.app-ph]. [3] E. L. Scheller et al., Inorganic Interpretation of Luminescent Materials Encountered by the Perseverance Rover on Mars, Science Advances, 10 (2024) 39, eadm8241 doi:10.1126/sciadv.adm8241 [4] S. J. VanBommel et al., Rare earth element assessment in Jezero crater using the Planetary Instrument for X-ray Lithochemistry on the Mars 2020 rover Perseverance: A case study of cerium, Icarus, 425 (2025) 116355. doi:10.1016/j.icarus.2024.116355 [5] C. M. Heirwegh et al., The Focused Beam X-ray Fluorescence Elemental Quantification Software Package PIQUANT, Spectrochim. Acta B, 196 (2022) 106520. doi:10.1016/j.sab.2022.106520. [6] J. L. Campbell et al., Calibration of the Mars Science Laboratory Alpha Particle X-ray Spectrometer. Space Sci. Rev. 170 (2012) 319 – 340. doi:10.1007/s11214-012-9873-5 [7] [6] T. Barber, S. Davidoff, W. T. Elam, C. M. Heirwegh (2022). pixlise/piquant: 2.0 open source migration release (v2.0). Zenodo. doi:10.5281/zenodo.6959126 PIXL and Mars 2020: https://science.nasa.gov/mission/mars-2020-perseverance/ XRF Fundamentals: R. Van Grieken, Handbook of X-Ray Spectrometry; B. Beckhoff, Handbook of Practical X-Ray Fluorescence Analysis
Student Requirements:	The candidate selected for this role should be enrolled in a university-level physical science or engineering degree program such as: experimental physics, geochemistry, geology, physical chemistry, materials science/engineering or a parallel field. In selecting a person for this role, qualities and skills in safe handling around fragile equipment, data analysis, organization of data, written and verbal communication, and aptitude to observing trends and peculiarities in data will all be considered desirable but not necessarily required. Past experience utilizing XRF spectrometer equipment, working with rock powder reference materials and working in a laboratory setting or on a research project in geo-chemistry or related field will also be considered favorably though not necessarily required. The selected candidate must be self-driven and able to work independently or on small teams, both with expectation of periodic support being provided by their advisor. The candidate must also take initiative to reach out for guidance when needed.
Location / Safety:	Project building and/or room locations: . Student will need special safety training: .
Programs:	This AO can be done under the following programs:   Program    Available To        SURF@JPL    both Caltech and non-Caltech students  Click on a program name for program info and application requirements.