Astrobiology

Introduction

Our research group is one of the partners at the New York Center for Astrobiology, based within the School of Science at Rensselaer Polytechnic Institute in Troy, N.Y. Professor Suzanne Baldwin, Research Associate Jayesh Das are collaborating with Professors John Delano (SUNY Albany), Bruce Watson (RPI), Tim Swindle (UA) and their respective research groups on the following projects.

Argon studies of hydrous K-bearing minerals on planetary surfaces

In the next decade, NASA plans a Mars Sample Return mission in which samples will be collected from carefully selected landing sites that are most promising as environments for present or past life. In preparation for a Mars sample return mission we are investigating terrestrial analogues of minerals known to exist on the Martian surface from data obtained by previous NASA missions. Among the minerals inferred from in situ measurements by the Opportunity Rover, K,Na-jarosite (K,Na)Fe3(SO4)2(OH)6 has the potential for revealing the age(s) when aqueous environments existed on Mars. We have experimentally determine the kinetics of argon in both natural jarosite. Why is this important? Results of argon diffusion experiments on jarosite will permit a more accurate interpretation of argon data obtained on jarosite samples on Earth , as well as samples returned from Mars.
Mars landscape
Figure 1. Image of jarosite-bearing Burns Formation taken by Opportunity at Burns cliff, Endurance Crater. (from Grotzinger et al., 2005).

Jarosite, a potassium (K) bearing sulphate, was discovered within Meridiani Planum sediments by the Opportunity exploration rover using a Mossbauer spectrometer (Klingelhofer et al., 2004).  Based on its occurrence on Earth, the presence of jarosite is an indicator of arid, acidic conditions following formation in a wet, acidic, and oxidizing environment (Fig. 2) (Elwood Madden et al., 2004).  As a K-bearing mineral jarosite can be dated using the 40Ar/39Ar method (e.g. Vasconcelos et al., 1994; Lueth et al., 2005).  Therefore, if jarosite-bearing samples were returned to Earth by future sample return missions to Mars, it is possible that the timing and rates of aqueous mineralization- and thus the time since an aqueous environment persisted on the Martian surface- could be determined by isotopically dating these minerals.

Pe-pH diagram
Figure 2. Pe-pH diagram indicating acidic, oxidizing conditions for jarosite formation. (from Catling, 2004)

In preparation for Mars sample return missions, we are investigating the argon retention properties of terrestrial jarosites.  Several samples have been provided by the Smithsonian Institution and others will be collected based on the applicability of their formation processes to those hypothesized for jarosite on Mars. The jarosite samples we have currently come from the Santa Eulalia district of Chihuahua, Mexico, the Mammoth Mine in the Tintic district in Utah, the Skouriotissa Mine in Cyprus, and the Meadow Valley mine in Pioche, Nevada.  These jarosite samples have been characterized chemically by electron microprobe prior to performing argon diffusion experiments.  Of importance is the abundance of potassium (K) in the samples (as wt% K2O), and the occurrence of chemically heterogeneous growth zoning (Fig. 3).  Knowing the amount of potassium in the sample (along with a rough estimate for the age of the mineral) allows for optimization of sample irradiation parameters. Knowledge of high and low-K zoning within a sample provides insights into interpreting complex age spectra.

thin section Jarosite
Figure 3. BSE (false colored) image of jarosite (blue and green) showing growth zoning. (from Burger et al., 2009).
Following chemical analyses, mineral separates are prepared for irradiation and vacuum furnace step-heating in the Syracuse University Noble Gas Isotope Research Laboratory (SUNGIRL). Results of Ar diffusion experiments can be found here (Kula & Baldwin, 2011). Based on these results, more detailed degassing experiments will be designed that investigate the diffusion of argon in jarosite over a range of pressure-temperature conditions.
element map
Figure 4 :Element maps for Smithsonian sample C7137 (Chihuahua, Mexico). Map at left: on the top (blue) is for sodium (Na) and map on the bottom (red) is for potassium (K). Note the scale bar is 500 µm. These maps indicate that this jarosite sample is coarse, K-rich (~9 wt%), and is homogeneous with respect to K-content (no zonation): all qualities required for the proposed argon diffusion studies.
thin section
Figure 5: Element maps for Smithsonian sample 104136 (Cyprus). Map at left: on the top (yellow) is for sodium (Na) and map on the bottom (blue) is for potassium (K). Note the scale bar is 200 µm. These maps show that this jarosite sample is not ideal for our initial argon diffusion experiments. It has abundant Na (~5 wt%) making it a natrojarosite, it exhibits K-zonation (heterogeneous distribution), and is finer grained that sample C7137.

 

Argon diffusion experiments on lunar impact glasses and lunar-analogue compositions

The goal of this project is to answer the question: “Does Ar remain trapped in lunar impact glasses over geologic time or does it slowly diffuse out of the glasses?” The answer to this question has major significance with respect to efforts over the past decade to date lunar impact glasses via the 40Ar/39Ar method. If Ar diffuses out of these glasses over the billions of years while potentially exposed on the lunar surface this will cause the ages reported from 40Ar/39Ar chronology to be younger than the impact event that formed them.

Over the past decade 40Ar/39Ar ages on impact material have been used to test hypotheses relating to the timing and existence of the late heavy bombardment, and to assess if impact frequency can be related to mass extinction events on Earth. Understanding if these 40Ar/39Ar ages are accurately recording the timing of impact events has major significance for interpreting these ages in the context of the solar system’s evolution.

We will build on our collaborators’ previous work (e.g., Zellner et al. 2002; Delano et al. 2007) that used 40Ar/39Ar dating of lunar impact glasses to investigate the bombardment history of the Earth/Moon system. Both lunar glasses collected by the Apollo missions, and synthesized lunar glass analogue material with chemical compositions similar to lunar impact glass material, will be used for argon diffusion studies. Apollo lunar glasses (1-1.5 mm in diameter) will be characterized by electron microprobe and micro-Raman spectroscopy and subsequently irradiated in a nuclear reactor. The diffusion systematics of argon in lunar impact glasses will be determined as a function of chemical composition, and results will be interpreted with respect to the proposed impact history of the Earth-Moon system.

impact-flux evolution
Figure 6: Proposed impact –flux evolution for the Early Earth-Moon system. Image courtesy of Bruce Watson.

 

Ar diffusion experiments on plagioclase feldspar

Feldspars have been inferred to exist (5–15%) in the sedimentary rocks at Meridiani Planum and are known to exist in igneous meteorites from Mars. We plan to test the strategy of using feldspars in martian regolith (e.g., basaltic eolian sands) to infer local/regional/global history of volcanism (and thereby episodes of atmosphere additions and resulting climate change). Argon diffusion experiments in plagioclase are planned to assess kinetic parameters. These will be used to interpret plagioclase 40Ar/39Ar age spectra. Results will allow assessment of whether terrestrial volcanic histories can be extracted from plagioclase detritus in eolian sands from well characterized protoliths which in turn will be used in developing sampling strategies for a sample return mission from Mars.

References

Burger, P.V., Papike, J.J., Shearer, C.K., and Karner, J.M., 2009, Jarosite growth zoning as a recorder of fluid evolution: Geochimica et Cosmochimica Act, v. 73, p. 3248-3259.

Catling, D.C., 2004, On Earth, as it is on Mars?: Nature, v. 429. p. 707-708.

Delano, J.W., Zellner, N.E.B., Barra, F., Olson, E., Swindle, T.D., Tibbetts, N.J., & Whittet, D.C.B. 2007, An integrated approach to understanding Apollo 16 impact glasses: Chemistry, isotopes and shape, Meteoritics Planetary Sci., 42, 993–1004

Elwood Madden, M.E., Bodnar, R.J., Rimstidt, J.D., 2004, Jarosite as an indicator of water-limited chemical weathering on Mars: Nature, v. 431, p. 821-823.

Grotzinger, J.P., Arvidson, R.E., Bell III, J.F., et al., 2005, Stratigraphy and sedimentology of a dry to wet eolian depositional system, Burns formation, Meridiani Planum, Mars: Earth and Planetary Science Letters, v. 240, p. 11-72.

Klingelhofer, G., Morris, R.V., Bernhardt, B., Schroder, C., Rodionov, D.S., de Souza Jr., P.A., Yen, A., Gellert, R., evlanov, E.N., Zubkov, B., Foh, J., Bonnes, U., Kankeleit, E., Gutlich, P., Ming, D.W., Renz, F., Wdowiak, T., Squyres, S.W., Arvidson, R.E., 2004, Jarosite and hematite at Meridiani Planum from Opportunity’s Mossbauer spectrometer: Science, v. 306, p. 1740-1745.

Lueth, V.W., Rye, R.O., and Peters, L., 2005, “Sour gas” hydrothermal jarosite: ancient to modern acid-sulfate mineralization in the southern Rio Grande Rift: Chemical Geology, v. 215, p. 339-360.

McDougall, I. and Harrison, T.M., 1999, Geochronology and Thermochronology by the 40 Ar/ 39 Ar Method, 2nd edition, Oxford University Press, New York, NY, 269 p.

Vasconcelos, P.M., Brimhall, G.H., Becker, T.A., and Renne, P.R., 1994, 40Ar/39Ar analysis of supergene jarosite and alunite: Implications to the paleoweathering history of the western USA and West Africa: Geochimica et Cosmochimica Acta, v. 58, p. 401-420.

Zellner, N.E.B., Spudis, P.D., Delano, J.W., & Whittet, D.C.B. 2002, Impact glasses from the Apol lo 14 landing site and implications for regional geology, J. Geophys. Res., 107, 1–13