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CheMin

XRD/XRF on Mars

The technology used in our XRD/XRF instruments derives directly from the NASA CheMin XRD/XRF instrument deployed on Mars Science Laboratory (MSL), also know as the Curiosity rover.

The name of CheMin makes reference to the science data ultimately obtained from its analyses: the instrument provides the Chemistry and the Mineralogy of a sample. CheMin has been successfully operated on Mars since 2012. It has analyzed 37 samples (as of early 2022) collected from the ground by the scoop and the percussion drill on the rover arm. The instrument is installed in the body of the rover and receives powder samples via the port at the top of the instrument.

Our staff was deeply involved in the development of CheMin, and remains engaged in a number of research programs associated with its operation on Mars, and the development of next generation XRD/XRF instruments for future missions.

Why Use XRD/XRF To Explore Mars?

Early Mars as we understand it had a lot of similarities with Earth.  It had oceans and rivers that shaped the surface with features we can observe today.  The atmosphere was thicker, temperatures less extreme.  Anywhere you look on Earth today, where these conditions are found, you find life.  Ancient Mars could have supported life.  The history of the red planet is mainly recorded in its rocks and their mineralogy.

Minerals are uniquely defined by their crystal structure and chemical formula. X-ray diffraction is the primary technique for the study of crystalline materials in general, and minerals in particular. Each crystal structure has a unique set of possible X-ray reflections that occur when a crystal is appropriately oriented in an X-ray beam, in respect with the Bragg equation. An X-ray diffraction analysis consists in the measurements of the angles and intensities at which crystalline matter reflects X-rays.

Powder X-ray diffraction is a practical implementation of XRD analysis for which the sample is ground into a powder, or naturally provided as a fine polycrystalline material. Definitive mineralogical analysis is typically approached by powder XRD. With powder XRD, the data either represent the unique signature of a single mineral, or is a weighted sum of all unique signatures in case of a mineral assemblage (rock or soil). 

X-ray fluorescence (XRF) allows the identification and quantitative measurement of chemical elements present in the sample. XRD and XRF are extraordinarily powerful when combined; they constitute the preferred method for mineralogical analysis of unknowns in terrestrial laboratories. In a complex sample such as a basalt, X-ray diffraction can identify and quantify all minerals, establish their individual elemental compositions and quantify the amount of the amorphous component. If coupled with XRF, the composition of the amorphous component can be determined as well.

CheMin Technology

CheMin was developed from ground up as a planetary instrument, using innovative concepts. In operation, a collimated X-ray beam from a microfocus X-ray tube is directed through a sample cell comprising two X-ray transparent windows separated by 175 μm and containing a powdered sample sieved to <150 μm.

The cell is shaken at sonic frequencies with the result that grains in the powder are placed in motion and exposed to the X-ray beam in random orientations during the analysis.

An X-ray sensitive Charge Couple Device (CCD) imager detects X-rays diffracted or fluoresced by the powder. The CCD is operated in single photon counting mode to allow measuring the charge generated by each photon (and hence its energy). A 2D image of the photons having the X-ray tube characteristic energy is computed to extract a diffraction pattern (elastic scattering), and then summed circumferentially to yield conventional XRD data. The energy histogram of all X-ray events detected provides the XRF data.

Geometry of the CheMin instrument. (left) Overall geometry of CheMin; (above right) XRD 2-theta plot obtained by summing diffracted photons from either of the characteristic lines of the X-ray source (Co K-alpha is colored magenta; (below right) X-ray energy-dispersive histogram obtained by summing all of the X-ray photons detected by the CCD (fluoresced photons from the sample shown schematically for elements Fe and lighter).
Illustration of CheMin dual-cell geometry. Exploded view of dual-cell assembly showing windows, tuning-fork assembly, and piezodriver (left). Assembled cell, ready for testing in testbed (right). The yellow Kapton window is on the left; the clear Mylar window is on the on right.

An example of CheMin data returned from Mars is shown below. Mineral abundances are derived using Rietveld refinement method. Quantitative results from CheMin data are shown in references. All CheMin XRD patterns, analysis results, and open access journal articles, are available and downloadable from https://odr.io/chemin.

First X-ray diffraction view of the Martian soil - CheMin analysis reveals feldspar, pyroxenes, olivine and more (Curiosity rover, "Rocknest", October 17, 2012).

Duetto: offspring of CheMin for Cultural Heritage

Duetto and CheMin have a lot in common:
  • the basic principle of X-ray detection using a cooled CCD in direct exposure,
  • the algorithms for extracting XRD and XRF data from a stream of X-ray images,
  • the miniature size and light weight.
The fundamental differences between the instruments are the nature of the sample and the geometry:
  • CheMin requires powdered samples to be inserted in the instrument for analysis in a transmission geometry,
  • Duetto analyses samples directly on the object, without collection and preparation, in a reflection geometry.
Starting with the CheMin design, we completely redesigned the geometry and system layout to offer a non-invasive instrument focused on Cultural Heritage applications.

Major findings from CheMin data

CheMin’s mineralogical analyses were critical to a number of first-of-their-kind achievements.  These include:
  • the first definitive mineralogical analysis of the Mars soil [1, 2],
  • the first identification of an ancient habitable environment on Mars [3, 4, 5],
  • the first in situ radiometric dating of the Mars surface [6],
  • the establishment of a maximum limit on the CO2 content of the Mars atmosphere in Hesperian time [7],
  • the first direct evidence of silicic volcanism on Mars [8],
  • the first ground-truth mineralogy used for orbital spectral measurements [9],
  • the first in situ evidence of the gradual drying out and oxidation of the Gale crater environment (and by proxy the early Mars atmosphere) [10].

References

  1. Blake D.F., R.V. Morris, G. Kocurek, S.M. Morrison, R.T. Downs, D. Bish, D.W. Ming, K.S. Edgett, D. Rubin, W. Goetz, M.B. Madsen, R. Sullivan, R. Gellert, I. Campbell, A.H. Treiman, S.M. McLennan, A.S. Yen, J. Grotzinger, D.T. Vaniman, S.J. Chipera, C.N. Achilles, E.B. Rampe, D. Sumner, P.-Y. Meslin, S. Maurice, O. Forni, O. Gasnault, M. Fisk, M. Schmidt, P. Mahaffy, L.A. Leshin, D. Glavin, A. Steele, C. Freissinet, R. Navarro-Gonzlez, R.A. Yingst, L.C. Kah, N. Bridges, K.W. Lewis, T.F. Bristow, J.D. Farmer, J.A. Crisp, E.M. Stolper, D.J. Des Marais, P. Sarrazin, and MSL Science Team. Curiosity at Gale crater, Mars: Characterization and analysis of the Rocknest sand shadow. Science, 341:1239505, 2013.
  2. Bish D.L., D.F. Blake, D.T. Vaniman, S.J. Chipera, R.V. Morris, D.W. Ming, A.H. Treiman, P. Sarrazin, S.M. Morrison, R.T. Downs, C.N. Achilles, A.S. Yen, T.F. Bristow, J.A. Crisp, J. M. Morookian, J.D. Farmer, E.B. Rampe, E.M. Stolper, N. Spanovich, and MSL Science Team. X-ray diffraction results from Mars Science Laboratory: Mineralogy of Rocknest aeolian bedform at Gale crater. Science, 341:1238932, 2013.
  3. Vaniman D.T., D.L. Bish, D.W. Ming, T.F. Bristow, R.V. Morris, D.F. Blake, S.J. Chipera, S.M. Morrison, A.H. Treiman, E.B. Rampe, M. Rice, C.N. Achilles, J.P. Grotzinger, S.M. McLennan, J. Williams, J.F. Bell, H.E. Newsom, R.T. Downs, S. Maurice, P. Sarrazin, A.S. Yen, J.M. Morookian, J.D. Farmer, K. Stack, R.E. Milliken, B.L. Ehlmann, D.Y. Sumner, G. Berger, J.A. Crisp, J.A. Hurowitz, R. Anderson, D.J. Des Marais, E.M. Stolper, K.S. Edgett, S. Gupta, N. Spanovich, and MSL Science team. Mineralogy of a mudstone at Yellowknife bay, Gale crater, Mars. Science, 343, 2014.
  4. Grotzinger J.P., D.Y. Sumner, L.C. Kah, K. Stack, S. Gupta, L. Edgar, D. Rubin, K. Lewis, J. Schieber, N. Mangold, R. Milliken, P.G. Conrad, D. DesMarais, J. Farmer, K. Siebach, F. Calef, J. Hurowitz, S.M. McLennan, D. Ming, D. Vaniman, J. Crisp, A. Vasavada, K.S. Edgett, M. Malin, D. Blake, R. Gellert, P. Mahaffy, R.C. Wiens, S. Maurice, J.A. Grant, S. Wilson, R.C. Anderson, L. Beegle, R. Arvidson, B. Hallet, R.S. Sletten, M. Rice, J. Bell, J. Griffes, B. Ehlmann, R.B. Anderson, T.F. Bristow, W.E. Dietrich, G. Dromart, J. Eigenbrode, A. Fraeman, C. Hardgrove, K. Herkenhoff, L. Jandura, G. Kocurek, S. Lee, L.A. Leshin, R. Leveille, D. Limonadi, J. Maki, S. McCloskey, M. Meyer, M. Minitti, H. Newsom, D. Oehler, A. Okon, M. Palucis, T. Parker, S. Rowland, M. Schmidt, S. Squyres, A. Steele, E. Stolper, R. Summons, A. Treiman, R. Williams, A. Yingst, and the MSL Science Team. A habitable fluvio-lacustrine environment at Yellowknife bay, Gale crater, Mars. Science, 343, 2014.
  5.  Bristow T.F., D.L. Bish, D.T. Vaniman, R.V. Morris, D.F. Blake, J.P. Grotzinger, E.B. Rampe, J.A. Crisp, C.N. Achilles, D.W. Ming, B.L. Ehlmann, P.L. King, J.C. Bridges, J.L. Eigenbrode, D.Y. Sumner, S.J. Chipera, J.M. Moorokian, A.H. Treiman, S.M. Morrison, R.T. Downs, J.D. Farmer, D. Des Marais, P. Sarrazin, M.M. Floyd, M.A. Mischna, and A.C. McAdam. The origin and implications of clay minerals from Yellowknife bay, Gale crater, Mars. American Mineralogist, 100:824–836, 2015.
  6. Farley K.A., C. Malespin, P. Mahaffy, J.P. Grotzinger, P.M. Vasconcelos, R.E. Milliken, M. Malin, K.S. Edgett, A.A. Pavlov, J.A. Hurowitz, J.A. Grant, H.B. Miller, R. Arvidson, L. Beegle, F. Calef, P.G. Conrad, W.E. Dietrich, J. Eigenbrode, R. Gellert, S. Gupta, V. Hamilton, D.M. Hassler, K.W. Lewis, S.M. McLennan, D. Ming, R. Navarro-González, S.P. Schwenzer, A. Steele, E.M. Stolper, D.Y. Sumner, D. Vaniman, A. Vasavada, K. Williford, R.F. Wimmer-Schweingruber, and the (MSL Science Team). In situ radiometric and exposure age dating of the martian surface. Science, 343, 2014.
  7. Bristow T.F., R.M. Haberle, D.F. Blake, D. Des Marais, J.L. Eigenbrode, A.G. Fairn, J.P. Grotzinger, K.M. Stack, M.A. Mischna, E.B. Rampe, K.L. Siebach, B.Sutter, D.T. Vaniman, and A.R. Vasavada. Low hesperian PCO2 from in situ mineralogical analysis at Gale crater, Mars. PNAS, 114:2166–2170, 2017.
  8. Morris R.V., D.T. Vaniman, D.F. Blake, R. Gellert, S.J. Chipera, E.B. Rampe, D.W. Ming, S.M. Morrison, R.T. Downs, A.H. Treiman, A.S. Yen, J.P. Grotzinger, C.N. Achilles, T.F. Bristow, J.A. Crisp, D.J. Des Marais, J.D. Farmer, K.V. Fendrich, J. Frydenvang, T.G. Graff, J.-M. Morookian, E. M. Stolper, and S.P. Schwenzer. Silicic volcanism on Mars evidenced by tridymite in high-SiO2 sedimentary rock at Gale crater. Proceedings of the National Academy of Sciences, 113:7071–7076, 2016.
  9. Achilles C.N., R.T. Downs, D.W. Ming, E.B. Rampe, R.V. Morris, A.H. Treiman, S.M. Morrison, A.S. Yen, D.T. Vaniman, D.F. Blake, T.F. Bristow, S.J Chipera, R.C. Ewing, B.L Ehlmann, J.A. Crisp, R. Gellert, K.V. Fendrich, P.I. Craig, J.P. Grotzinger, D.J. Des Marais, J.D. Farmer, P.C. Sarrazin, and J.M. Morookian. Mineralogy of an active eolian sediment from the Namib dune, Gale crater, Mars. Journal of Geophysical Research: Planets, 122:2344–2361, 2017.
  10. Bristow T.F., E.B. Rampe, C.N. Achilles, D.F. Blake, S.J. Chipera, P. Craig, J.A. Crisp, D.J. Des Marais, R.T. Downs, R. Gellert, J.P. Grotzinger, R.M. Hazen, B. Horgan, J.V. Hogancamp, N. Mangold, P. Mahaffy, A.C. McAdam, D.W. Ming, J.M. Morookian, R.V. Morris, S.M. Morrison, A.H. Treiman, D.T. Vaniman, A. Vasavada, and A.S. Yen. Clay mineral diversity and abundance in sedimentary rocks of Gale crater, Mars. Science Advances, 4, no. 6, eaar3330, 2018.