Crystals in Space – How we study them and what they tell us
NASA Ames Research Center
Minerals are crystalline phases with known conditions of formation. Minerals can persist outside their stability fields for geologically long periods of time, so we can study the conditions of their formation long afterward – up to and beyond the age of our solar system. I and my colleagues at NASA have been privileged to study a number of interesting problems whose ultimate solution involves mineralogy and crystallography, including:
Interstellar ice. Cold molecular clouds are the birthplace of stars and the source of the first abiotic organic compounds, precursors to life. Astronomical observations of cold molecular clouds at infrared wavelengths, coupled with terrestrial laboratory analyses of ice structure demonstrate that thermally induced structural changes in the ice dictate the origin and timing of organic compound formation and the delivery of organic compounds to habitable zones in stellar nebulae (Blake, et al., 1991; Jenniskens and Blake, 1994).
Interplanetary dust. NASA deploys ER-2 aircraft in the stratosphere to collect interplanetary dust particles, 5-100µm composite grains that originate from comets and asteroids. These particles have remained essentially unaltered since the origin of the solar system, and provide clues to the early solar system and the delivery of the biogenic elements to Earth.
Meteorites and the condition(s) of the early solar system. Meteorites are leftover debris from the formation and destruction of planetesimals in the early solar system, 4.54 billion years ago. Investigations into the mineralogy of meteorites tell us about the conditions that were present when the solar system formed, and the source(s) of the crystalline materials. All meteorites contain a tiny fraction (<100 ppm) of diamond that trapped isotopically anomalous xenon during its formation. The isotopic makeup of the xenon tells us that this diamond originated in stellar outflows predating the solar system (Lewis et al., 1987 and references therein; Blake et al., 1988). Several other minerals present in meteorites at trace levels reveal other aspects of star formation and pre-solar history.
Life in Martian Meteorites? In 1994 it was reported that certain meteorites had originated from Mars, on the basis of trapped gas in shocked glass of the meteorites that corresponded to the composition of the Mars atmosphere. In 1996, McKay and co-authors reported purported evidence for early microbial life in the 3.85 billion year old Mars meteorite ALH84001. Follow-on work (using crystallographic techniques) has shown that these observations are more reasonably explained as natural, abiotic processes (e.g., Treiman et al., 2002).
Robotic mineral analysis on Mars. In 2012, NASA’s Mars Science Laboratory rover Curiosity landed in Gale crater, Mars. One of the payload instruments in the analytical laboratory of Curiosity is CheMin, the first X-ray Diffractometer sent to another planet (Blake et al., 2012). In the following two years on Mars, CheMin delivered the first quantitative and definitive mineralogic analysis of the Mars soil (Bish et al., 2013; Blake et al, 2013), and provided mineralogical data that were the basis for the discovery of the first habitable environment on another planet (Vaniman, et al., 2014; Grotzinger, et al., 2014) – the success criterion for Curiosity’s 2.5 billion dollar mission.
Bish, D.L., et al. (2013). “X-Ray Diffraction Results from Mars Science Laboratory: Mineralogy of Rocknest Aeolian Bedform at Gale crater.” Science, 341, 1238932; doi: 10.1126/science.1238932.
Blake, D.F., et al. (1988). “The nature and origin of interstellar diamond.” Nature, 332, No. 6165, pp. 611-613.
Blake, D.F., et al. (1991). “Clathrate Hydrate Formation in Amorphous Cometary Ice Analogs in Vacuo.” Science, 254, 548-551.
Blake, D.F., et al. (2012). “Characterization and Calibration of the CheMin Mineralogical Instrument on Mars Science Laboratory.” Space Science Reviews, Vol. 170, Issue 1-4, pp. 341-399.
Blake, D.F., et al.(2013). “Curiosity at Gale crater, Mars: Characterization and analysis of the Rocknest sand shadow.” Science, 341, 1239505; doi:10.1126/science.1239505.
Grotzinger, J. P. et al. (2013). “A Habitable Fluvio-Lacustrine Environment at Yellowknife Bay, Gale Crater, Mars.” Science, 10.1126/science.1242777.
Jenniskens, P. and D.F. Blake (1994). “Structural transitions in amorphous water ice and astrophysical implications.” Science 265:753–756.
Lewis, R. S.; et al., (1987). “Interstellar diamonds in meteorites.” Nature (ISSN 0028-0836), vol. 326, March 12, 1987, p. 160-162. NASA-supported research.
McKay, D.S., et al., (1996) “Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001.” Science 16 August 1996: Vol. 273 no. 5277 pp. 924-930. DOI: 10.1126/science.273.5277.924
Treiman, A.H., et al., (2002). “Hydrothermal origin for carbonate globules in Martian meteorite ALH84001: A terrestrial analogue from Spitsbergen (Norway).” Earth and Planetary Science Letters 204, 323–332.
Vaniman, D.T., et al. (2013). “Mineralogy of a Mudstone on Mars.” Science, 10.1126/science.1243480.