Dr. Chris Heirwegh
Lead for the team of JPL scientists and affiliates

Dr. Chris Heirwegh is a Scientist and Science Operations Manager of team PIXL, Planetary Instrument for X-ray Lithochemistry, at NASA’s Jet Propulsion Laboratory (JPL). His main expertise is in the physics fundamentals of X-ray spectroscopy and its applications in geochemical planetary exploration.

Born and raised in Simcoe Ontario, Canada, Chris wished to be a pharmacist and pharmacy business owner like his father. However, his interests and search for answers took him on a different path. Chris had been intrigued with science from an early age and was always interested in learning why something worked or didn’t work. He completed a BSc in Physical Sciences and a MSc in Medical Physics from McMaster University in 2004 and 2009, respectively. During his Master’s degree, Chris studied in vivo elemental abundance, which looked at elements such as lead and strontium in bone and arsenic in skin using X-ray fluorescence (XRF) spectroscopy techniques.

After the completion of his MSc degree, Chris realized that even with all the measurements he had acquired and analyzed using XRF, he still didn’t grasp much of the physics behind the applications. To develop a deeper comprehension of the physical techniques, he joined a group at the University of Guelph that studied XRF and particle-induced X-ray emission (PIXE) processes. He also studied how fundamental physics of X-ray emission is used in the composition analysis of materials. This group happened to be involved with the alpha-particle X-ray spectrometer (APXS) devices on the Mars exploration rovers (MER), Spirit and Opportunity, and Mars Science Lab (MSL), a robotic spacecraft that landed the Curiosity rover, which gave Chris the opportunity to learn about the Mars missions and he also found that his expertise was a valuable asset. With his growing interest in planetary science exploration, he stayed at the University of Guelph to pursue a postdoctoral fellowship after completing his PhD. When he started looking for jobs, he talked to Professor Tim Elam, a spectroscopist of PIXL, who connected him to Abigail Allwood, Principal Investigator of PIXL. He worked as a postdoctoral fellow for two years at JPL before being hired full time as a scientist.

Dr. Heirwegh has contributed to two separate NASA missions to Mars that have sent rovers, Curiosity and Perseverance. On Curiosity, he played more of a supporting role and provided analytical expertise for analyzing data from the APXS. On Perseverance, he is directly involved as a scientist and is the PIXL team’s Science Operations Manager. He leads a team of scientists from JPL and experts from various institutions, who participate in operations. He has also co-developed the XRF quantification software, known as the PIQUANT, used by the PIXL team to analyze data returned from Mars. With Curiosity, Dr. Heirwegh learned about mission constraints which allowed him to develop an appreciation for the time and rover power required to obtain data. This knowledge helped very much when he began working on PIXL, NASA’s most current XRF spectrometer, mounted on board the Perseverance rover.

PIXL is an instrument used to quantify different elemental constituents in rocks. Scientists must convert raw signals from Mars to meaningful data on Earth. To do this accurately, the instrument must be calibrated. When asked how calibration is conducted on Mars, Dr. Heirwegh explained that it began on Earth. The PIXL sensor head was placed in front of a calibration target inside a Mars-simulated environment. With PIXL now attached to the arm of Perseverance, the consistency of the calibration is checked every couple of months. If the X-ray response stays constant over time, recalibration is not required; however, if it were to change, a new calibration using this target would be performed. Calibration standards include a Teflon^® blank (to assess the raw beam), and three geologically relevant materials such as BHVO2-G, an acronym for Basaltic Hawaiian Volcanic Ocean glass taken from the site of an eruption from 1919. Each material contains homogeneous mixtures of many rock-forming elements including: silicon, calcium and iron. Another key part of the calibration is to ensure that PIXL’s camera images of a rock target can be co-registered to the 2D elemental map data recorded by its X-ray system. Co-registration is made possible using a pre-programmed camera model. Model consistency is assessed by overlaying camera images of the calibration target with X-ray data recorded by scanning a central cross-hairs target and four corner fastener screws. As long as the two datasets align when co-registered, the camera model can be left alone.

Dr. Heirwegh also explained that PIXL is equipped with a hexapod system—six mechanical struts that are essentially moving pistons. They give PIXL the flexibility to move and raster scan a target to produce a pixelated rectangular elemental map image of a rock target. All six hexapods have a mathematical construct which tells which strut to move and by how much. This kind of technology is unique in that on Earth, one would use a handheld XRF device for measurement in the field or a much larger human-sized spectrometer, which would be too cumbersome to transport to Mars.

Jezero crater, the landing site of Perseverance, was believed to be formed by meteoritic impact. The question scientists asked: are the rocks igneous, formed from lava flow; or are they sedimentary, formed from sand, silt or organic debris? Through map scans, PIXL confirmed that the rocks that made up the crater floor were indeed igneous. The samples were found to contain very coarse crystalline minerals such as augite, feldspar, and Fe-Cr-Ti oxides, strongly indicating an igneous nature. PIXL also helped uncover the likelihood of water present at one time, as rocks contained salt precipitates and the minerals showed signs of being cooled in water. The rover has now left the crater floor and has moved toward the river delta, a region where scientists expect might possess organic matter and evidence of ancient life.

Day to day, Dr. Heirwegh’s role changes with different priorities. Some days he takes on more of an administrative role—coordinating schedules, handling staffing issues and working on process improvements—whereas other days, he works on operations, training or carrying out research. Dr. Heirwegh’s research team focuses on advancing analytical techniques that improve the accuracy of XRF to analyze composition materials and also developing XRF instrumentation for potential future in situ planetary explorations. One of his current projects assesses the feasibility of using pyroelectric X-ray emission technology as an X-ray source alternative to radioactive source and electrically driven tube emitters. He is currently working on papers about the PIQUANT software package and the elemental calibration of PIXL. Furthermore, Dr. Heirwegh and his team are investigating the potential of PIXL or similar instrumentation for future missions, for example, to an outer planet moon like Europa.

Dr. Heirwegh’s thirst for knowledge and ambition led him to where he is today, but he also emphasizes the importance of a well-balanced life. Rest and exercise keep him alert for whatever needs to be tackled day to day. He works hard in his professional career but takes time out of his busy schedule to spend time with his family. He enjoys travelling and exploring the west coast of the United States, hiking and taking road trips.

When asked whether he would ever travel to Mars if it became possible, he answered “no” as space travel takes a long time and he would miss his family too much.

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