2009 Annual Science Report
Rensselaer Polytechnic Institute Reporting | JUL 2008 – AUG 2009
Project 5: Vistas of Early Mars: In Preparation for Sample Return
To understand the history of life in the solar system requires knowledge of how hydrous minerals form on planetary surfaces, and the role these minerals play in the development of potential life forms. One hydrous mineral found on Earth and inferred from in situ measurements on Mars, is the mineral Jarosite, KFe3(SO4)2(OH)6. We are investigating whether radiometric ages, specifically 40Ar/39Ar ages on jarosite can be interpreted to accurately record climate change events on Mars. This project not only requires understanding the conditions required for jarosite formation and preservation on planetary surfaces, but also assessing under what conditions its “radiometric clock” can be reset (e.g., during changes in environmental conditions such as temperature). By studying jarosites formed by a variety of processes on Earth, we will be prepared to analyze and properly interpret ages measured from jarosite obtained from future Mars sample return missions.
A literature review of 40Ar/39Ar analyses on terrestrial jarosite was undertaken to ascertain argon release patterns for jarosite under ultrahigh vacuum conditions. It was found that the majority of published 40Ar/39Ar jarosite data was generated using lasers to release argon. Data produced via vacuum furnace heating were unfortunately reported without analytical parameters necessary for proper estimation of argon degassing behaviors (i.e., temperature). However, the mined data afforded evaluation of the percent volume of gas released at a given furnace temperature set point (Figure 1). While not diagnostic of diffusion kinetics for jarosite, previously published data indicates jarosite tends to outgas at significantly lower temperatures than minerals typically analyzed by the 40Ar/39Ar method. Our compilation will aid in the design of proposed diffusion experiments using a double vacuum resistance heated furnace with temperature control monitored via a thermocouple assembly.
Four jarosite samples were obtained from the Smithsonian Institute for argon diffusion experiments. These include NMNH C7137 from Santa Eulalia District, Chihuahua, Mexico; NMNH R6303 from the Mammoth Mine, Tintic District, Utah, USA; NMNH R6299 from Meadow Valley Mine, Pioche, Nevada, USA; and NMNH 104139 from Skouriotissa Mine, Cyprus. No documentation is available regarding the petrogenesis for these samples. Sample characterization via electron microprobe (EMPA) was undertaken and indicates that some Smithsonian Institute jarosites are of sufficient quality/quantity for initial argon diffusion experiments (Table 1; Figure 2). Based in part on EMPA chemical data, samples for initial argon diffusion studies have been selected and mineral separates prepared for upcoming irradiation and preliminary 40Ar/39Ar analyses.
New collaborations have been established in preparation for fieldwork to collect additional jarosite samples for argon diffusion experiments (for details see collaborations section of this report). A permit application to collect jarosite samples at Kilauea volcano has been submitted and potential collaborations established for geologic fieldwork. Arrangements have also been made through collaborators to sample paleosol-hosted jarosite in the Bighorn Basin in July 2010. Jarosite samples from Iceland have been collected and are being shipped to Syracuse University.
PROJECT INVESTIGATORS:Suzanne Baldwin
Project InvestigatorJoseph Kula
PROJECT MEMBERS:John Delano
RELATED OBJECTIVES:Objective 1.1
Formation and evolution of habitable planets.
Biosignatures to be sought in Solar System materials