I work with the Curiosity and Opportunity Mars rovers to better understand past and present processes on Mars. Each rover is equipped with an Alpha Particle X-ray Spectrometer (APXS) to investigate the chemical composition of Martian rocks and soils. My research focuses on expanding the capabilities of each APXS instrument and enhancing the scientific return of their respective data sets. Exploring Mars through the eyes of rovers, living on "Mars time", and working with amazing (and brilliant!) colleagues has made for a fun and rewarding career thus far.
Department of Earth and Planetary Science
Mars Science Laboratory Science Team
Department of Earth and Planetary Science
Mars Exploration Rover Science Team
University of Guelph
Department of Physics
University of Guelph
Department of Physics
University of Guelph
Department of Physics
(with Distinction)
Figure 1
The Alpha Particle X-ray Spectrometer (APXS) is a device that can determine the composition of Martian rocks and soils without a trace that it was there. You can think of the APXS as a real-life Martian version of a Star Trek tricorder, but for rocks. As you might imagine, placing the APXS on the desired target (see Fig. 1) is not straight-forward given it is on another planet. Thankfully, there is a fantastic team who specialize in interpreting the images we get from Mars and positioning the APXS onto the target with the giant robotic arm. Many factors can cause the positioning to differ from the intended location, albeit by a small amount.
The APXS uses a non-destructive technique (i.e. we don't leave a mark). In regions were there are differences in chemistry within the APXS field of view (e.g. Fig. 2), it becomes increasingly important to know as accurately as possible where the APXS was located in order to determine an accurate composition for each unique chemical component.
Figure 2
Figure 3
One way to tackle uncertainty in the exact APXS placement is through utilizing a "raster". A raster is how we describe a technique where several APXS measurements are conducted in close proximity around the intended target (e.g. Fig. 2). When the target has a unique chemistry that correlates to what we can see in images, we can use the chemistry information from the APXS and the accompanying images to not only determine a better APXS location (e.g. Fig. 2) but also determine the chemistry of each component in the target area (e.g. Fig. 3).
The data the APXS acquires on Mars has to be analyzed to determine the composition of the sample. When data is transmitted from Mars to Earth with the help of satellites orbiting Mars, it is in the form of a spectrum (e.g. Fig. 4, simulated). You can think of a spectrum as a histogram of X-rays detected at various energies. In this histogram, peaks are clearly visible. Each peak corresponds to a specific element (or in some cases elements). The composition of the sample is determined from an analysis of the spectrum.
Figure 4
Figure 5
The APXS has acquired thousands of spectra on Mars and we have a solid understanding of its performance. We can use this vast database of spectra to predict what a spectrum will look like given various parameters. Based on a given rock composition, alongside other experimental parameters such as temperature, we can use our predicted spectrum to understand data we observe from Mars better and conduct virtual experiments here on Earth using an instrument that is already on Mars (e.g. Fig. 5).
We can also analyze these predictive spectra as if they were acquired on Mars. In doing so, we can test the instrument in this virtual environment and derive an understanding not possible in a laboratory on Earth. For example, a thorough calibration of the APXS was conducted before launch. However, conditions were kept as ideal as possible in order to achieve the a high level of accuracy. On Mars however, conditions are not always ideal. In creating a series of predicted spectra, we can further instrument calibration while it is on Mars. One such example of this is illustrated in Fig. 6, demonstrating the our ability to detect a given element depending on the temperature and measurement duration.
Figure 6
Figure 7
The APXS was designed to measure solid samples such as rocks and soils. However, one of the peaks that appears in APXS spectra comes from argon in the atmosphere of Mars (e.g. Fig. 4). Even though the atmosphere of Mars contains less than 2% argon, not only can the APXS detect it, but we are able to monitor changes in the abundance of argon in the atmosphere. Because Mars gets so cold, at the winter pole, CO2 "freezes out" of the atmosphere. Argon however, does not. Since Curiosity's APXS cannot detect CO2 (which makes up ~95% of Mars' atmosphere), the changes in argon observed (e.g. Fig. 7) correspond directly to changes in the abundance of argon in the atmosphere at the rover's location. From our understanding of the seasonal pressure cycle, we can determine how the fraction of argon in the atmosphere changes over time. This also tells us how other elements in the atmosphere behave, furthering our understanding of global environmental systems on Mars.
Antarctica's empty, ice-covered expanse makes the continent ideal for spotting space debris.
Hundreds gathered at the University of Guelph to view the partial solar eclipse on Monday afternoon.
A student at the University of Guelph has been shortlisted by the Canadian Space Agency to become Canada’s next astronaut.
Campus presentation for families outlines space research being conducted at the U of G, including work for the Mars Rover project.
Peer-Reviewed Publications
20 - S. J. VanBommel, R. Gellert, N. I. Boyd, J. A. Berger and A. S. Yen (2019), Mars Science Laboratory Alpha Particle X-ray Spectrometer Trace Elements: Situational Sensitivity to Co, Ni, Cu, Zn, Ga, Ge, and Br. Acta Astronautica, 165, 32-42.
19 - S. J. VanBommel, R. Gellert, N. I. Boyd, and J. U. Hanania (2019), Empirical Simulations for Further Characterization of the Mars Science Laboratory Alpha Particle X-ray Spectrometer: An Introduction to the ACES Program. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 441, 79-87.
18 - J. L. Campbell, D. D. Thompson, E. L. Flannigan, N. G. Holmes, D. W. Tesselaar, and S. J. VanBommel (2019), A re-examination of the fundamental parameters approach to calibration of the Curiosity rover Alpha Particle X-ray Spectrometer. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 447, 22-29.
17 - R. E. Kronyak, L. C. Kah, K. S. Edgett, S. J. VanBommel, L. M. Thompson, R. C. Wiens, V. Z. Sun, and M. Nachon (2019) Mineral-filled fractures as indicators of multigenerational fluid flow in the Pahrump Hills member of the Murray formation, Gale Crater, Mars. Earth and Space Science, Accepted.
16 - S. J. VanBommel, R. Gellert, B. C. Clark, and D. W. Ming (2018), Seasonal Atmospheric Argon Variability Measured in the Equatorial Region of Mars by the Mars Exploration Rover Alpha Particle X-Ray Spectrometers: Evidence for an Annual Argon-Enriched Front. Journal of Geophysical Research: Planets, 123, 2.
15 - V. Z. Sun, K. M. Stack, L. C. Kah, L. M. Thompson, W. Fischer, A. J. Williams, S. S. Johnson, R. C. Weins, R. E. Kronyak, M. Nachon, C. H. House, and S. J. VanBommel, (2018), Late-Stage Diagenetic Concretions in the Murray Formation, Gale Crater, Mars. Icarus, 321, 866-890.
14 - D. W. Mittlefehldt, R. Gellert, S. J. VanBommel, D. W. Ming, A. S. Yen., B. C. Clark, R. V. Morris, C. Schröder, L. S. Crumpler, J. A. Grant, B. L. Jolliff, R. E. Arvidson, W. H. Farrand, K. E. Herkenhoff, J. F. Bell III, B. A. Cohen, G. Klingelhöfer, C. M. Schrader, and James W. Rice, (2018), Diverse Lithologies and Alteration Events on the Rim of Noachian-Aged Endeavour Crater, Meridiani Planum, Mars: In Situ Compositional Evidence. Journal of Geophysical Research: Planets, 123, 5.
13 - C. D. O'Connell-Cooper, L. M. Thompson, J. G. Spray, J. A. Berger, S. J. VanBommel, R. Gellert, N. I. Boyd, and E. D. DeSouza, (2018), Chemical diversity of sands within the linear and barchan dunes of the Bagnold Dunes, Gale Crater, as revealed by APXS onboard Curiosity. Geophysical Research Letters, 45.
12 - N. T. Stein, R. E. Arvidson, J. A. O'Sullivan, J. G. Catalano, E. A. Guinness, D. V. Politte, R. Gellert, and S. J. VanBommel, (2018), Retrieval of Compositional End-Members From Mars Exploration Rover Opportunity Observations in a Soil-Filled Fracture in Marathon Valley, Endeavour Crater Rim. Journal of Geophysical Research: Planets, 123, 278-290.
11 - S. J. VanBommel, R. Gellert, J. A. Berger, L. M. Thompson, K. S. Edgett, M. J. McBride, M. E. Minitti, N. I. Boyd, and J. L. Campbell (2017), Modeling and mitigation of sample relief effects applied to chemistry measurements by the Mars Science Laboratory Alpha Particle X-ray Spectrometer. X-Ray Spectrometry, 46, 229-236.
10 - J. A. Berger, M. E. Schmidt, R. Gellert, N. I. Boyd, E. D. Desouza, M. R. Izawa, D. W. Ming, G. M. Perrett, E. B. Rampe, S. J. VanBommel, and A. S. Yen, (2017), Zinc and germanium in the sedimentary rocks of Gale Crater on Mars indicate hydrothermal enrichment followed by diagenetic fractionation. Journal of Geophysical Research: Planets, 122, 8, 1747-1772.
09 - C. D. O'Connell-Cooper, J. G. Spray, L. M. Thompson, R. Gellert, J. A. Berger, N. I. Boyd, E. D. Desouza, G. M. Perrett, M. Schmidt, S. J. VanBommel, (2017), APXS-derived chemistry of the Bagnold dune sands: Comparisons with Gale Crater soils and the global Martian average. Journal of Geophysical Research: Planets, 122, 2623-2643.
08 - S. J. VanBommel, R. Gellert, J. A. Berger, J. L. Campbell, L. M. Thompson, K. S. Edgett, M. J. McBride, M. E. Minitti, I. Pradler, and N. I. Boyd, (2016), Deconvolution of distinct lithology chemistry through oversampling with the Mars Science Laboratory Alpha Particle X-ray Spectrometer. X-Ray Spectrometry, 45, 3, 155-161.
07 - R. E. Arvidson, S. W. Squyres, R. V. Morris, A. H. Knoll, R. Gellert, B. C. Clark, J. G. Catalano, B. L. Jolliff, S. M. McLennan, K. E. Herkenhoff, S. J. VanBommel, D. W. Mittlefehldt, J. P. Grotzinger, E. A. Guinness, J. R. Johnson, J. F. Bell III, W. H. Farrand, N. Stein, V. K. Fox, M. A. Hinkle, W. M. Calvin, and P. A. de Souza Jr, (2016), High Concentrations of Manganese and Sulfur in Deposits on Murray Ridge, Endeavour Crater, Mars. American Mineralogist, 101, 6.
06 - J. A. Berger, M. E. Schmidt, R. Gellert, J. L. Campbell, P. L. King, R. L. Flemming, D. W. Ming, B. C. Clark, I. Pradler, S. J. VanBommel, M. E. Minitti, A. G. Fairén, N. I. Boyd, L. M. Thompson, G. M. Perrett, B. E. Elliott, and E. Desouza, (2016), A global Mars dust composition refined by the Alpha-Particle X-ray Spectrometer in Gale Crater. Geophysical Research Letters, 43, 67-75.
05 - L. M. Thompson, M. E. Schmidt, J. G. Spray, J. A. Berger, A. G. Fairén, J. L. Campbell, G. M. Perrett, N. I. Boyd, R. Gellert, I. Pradler, and S. J. VanBommel, (2016), Potassium-rich sandstones within the Gale impact crater, Mars: The APXS perspective. Geophysical Research Letters, 121, 10, 1981-2003.
04 - N. L. Lanza, R. C. Wiens, R. E. Arvidson, B. C. Clark, W. W. Fischer, R. Gellert, J. P. Grotzinger, J. A. Hurowitz, S. M. McLennan, R. V. Morris, M. S. Rice, J. F. Bell III, J. A. Berger, D. L. Blaney, N. T. Bridges, F. Calef III, J. L. Campbell, S. M. Clegg, A. Cousin, K. S. Edgett, C. Fabre, M. R. Fisk, O. Forni, J. Frydenvang, K. R. Hardy, C. Hardgrove, J. R. Johnson, J. Lasue, S. Le Mouélic, M. C. Malin, N. Mangold, D. W. Ming, H. E. Newson, A. N. Ollila, V. Sautter, S. Schröder, L. M. Thompson, A. H. Treiman, S. J. VanBommel, D. T. Vaniman, and M. Zorzano, (2016), Oxidation of manganese in an ancient aquifer, Kimberley formation, Gale crater, Mars. Geophysical Research Letters, 43, 14, 7398-7407.
03 - J. A. Berger, P. L. King, R. Gellert, J. L. Campbell, N. I. Boyd, I. Pradler, G. M. Perrett, K. S. Edgett, S. J. VanBommel, M. E. Schmidt, and R. E. Lee, (2014), MSL-APXS titanium observation tray measurements: Laboratory experiments and results for the Rocknest fines at the Curiosity field site in Gale Crater, Mars. Journal of Geophysical Research: Planets, 119, 1046-1060.
02 - M. E. Schmidt, J. L. Campbell, R. Gellert, G. M. Perrett, A. H. Treiman, D. K. Blaney, A. Olilla, F. J. Caleff III, L. Edgar, B. E. Elliott, J. P. Grotzinger, J. Hurowitz, P. L. King, M. E. Minitti, V. Sautter, K. Stack, J. A. Berger, J. C. Bridges, B. L. Ehlmann, O. Forni, L. A. Leshin, K. W. Lewis, S. M. McLennan, D. W. Ming, H. Newsom, I. Pradler, S. W. Squyres, E. M. Stolper, L. M. Thompson, S. J. VanBommel, and R. C. Wiens, (2014), Geochemical diversity in first rocks examined by the Curiosity Rover in Gale Crater: Evidence for and significance of an alkali and volatile-rich igneous source. Journal of Geophysical Research: Planets, 119, 1, 64-81.
01 - S. M. McLennan, R. B. Anderson, J. F. Bell III, J. C. Bridges, F. Calef III, J. L. Campbell, B. C. Clark, S. Clegg, P. Conrad, A. Cousin, D. J. Des Marais, G. Dromart, M. D. Dyar, L. A. Edgar, B. L. Ehlmann, C. Fabre, O. Forni, O. Gasnault, R. Gellert, S. Gordon, J. A. Grant, J. P. Grotzinger, S. Gupta, K. E. Herkenhoff, J. A. Hurowitz, P. L. King, S. Le Mouélic, L. A. Leshin, R. Léveillé, K. W. Lewis, N. Mangold, S. Maurice, D. W. Ming, R. V. Morris, M. Nachon, H. E. Newsom, A. M. Ollila, G. M. Perrett, M. S. Rice, M. E. Schmidt, S. P. Schwenzer, K. Stack, E. M. Stolper, D. Y. Sumner, A. H. Treiman, S. J. VanBommel, D. T. Vaniman, A. Vasavada, R. C. Wiens, and R. A. Yingst, (2014), Elemental Geochemistry of Sedimentary Rocks at Yellowknife Bay, Gale Crater, Mars. Science, 343, 6169.
Lead-Author Conference Presentations
2019 European Planetary Science Congress (Geneva, Switzerland, 19 September 2019) The Mars Year 34 Global Dust Storm and Atmospheric Measurements with Multiple Generations of Alpha Particle X-ray Spectrometers.
2019 European Planetary Science Congress (Geneva, Switzerland, 16 September 2019) High-Fidelity Simulations of Mars Science Laboratory Alpha Particle X-ray Spectrometer Spectra: Enhanced Characterization and Results from Gale.
50th Lunar and Planetary Science Conference (Houston, TX, 19 March 2019) Low-Latitude Near-Antipode Measurements of Atmospheric Argon With the Mars Exploration Rover and Mars Science Laboratory Alpha Particle X-ray Spectrometers.
50th Lunar and Planetary Science Conference (Houston, TX, 19 March 2019) Enhanced Characterization of the Mars Science Laboratory Alpha Particle X-ray Spectrometer Through Analyses of Software-Simulated Spectra.
49th Lunar and Planetary Science Conference (Houston, TX, 20 March 2018) Six Mars Years of Atmospheric Argon Measurements with the Mars Exploration Rover Alpha Particle X-ray Spectrometers.
2017 European Geosciences Union (Vienna, Austria, 26 April 2017) Representative composition of the Murray Formation, Gale Crater, Mars, as refined through modeling utilizing Alpha Particle X-ray Spectrometer observations.
48th Lunar and Planetary Science Conference (Houston, TX, 21 March 2017) Refined chemical composition of the Murray Formation, Gale Crater, Mars, as modeled with observations by the Alpha Particle X-ray Spectrometer.
2017 American Physical Society March Meeting (New Orleans, LA, 14 March 2017) In Situ Sub-cm Chemistry for Assessing Ancient Habitability on Mars with the Alpha Particle X-ray Spectrometer.
2016 American Geophysical Union (San Francisco, CA, 13 December 2016) Automated Grouping of Opportunity Rover Alpha Particle X-ray Spectrometer Data.
2016 Canadian Association of Physicists Congress (Ottawa, ON, 16 June 2016) Advancing Canada’s Martian In Situ Spectrometer: Sub-cm Chemistry for the Ongoing Assessment of Past Habitability on Mars.
2016 European Geosciences Union (Vienna, Austria, 18 April 2016) Millimeter-scale chemistry of observable endmembers with the Mars Science Laboratory Alpha Particle X-Ray Spectrometer and Mars Hand Lens Imager.
47th Lunar and Planetary Science Conference (Houston, TX, 24 March 2016) Chemistry of millimeter-scale petrographic endmembers determined by the Mars Science Laboratory Alpha Particle X-ray Spectrometer and Mars Hand Lens Imager.
46th Lunar and Planetary Science Conference (Houston, TX, 19 March 2015) APXS Raster Localization using MAHLI-Distinguishable Phases: Localization and Phase Chemistry Including the Diagenetic Feature “Morrison”.
