I am a participating scientist with the Mars Science Laboratory (MSL) mission. Working with collaborator Paulo Vasconcelos and Caltech graduate student Hayden Miller, we aim to implement surface exposure and radiometric dating methods on Mars using the MSL rover’s onboard analytical suite. Currently, not a single direct age determination informs the Martian timescale. The MSL rover will be landing within Gale Crater at the base of a 5.2 km mound of stratified material that is primarily sedimentary in origin. The lower formation of the mound displays a transition from clay- dominated mineralogy towards sulfate/oxide assemblages, interpreted to be a record of global scale changes in aqueous and climate conditions of Mars.
Light noble gases (He, Ne, Ar) carry the ability to provide insight into Mars’ history. Isotopes of these gases produced by cosmic ray reactions in the upper few meters of Mars’ surface can provide a quantitative understanding of Mars’ history that has never been achieved. The determination of cosmogenic noble gas concentrations can determine ages of youthful features such as impact craters, landslides and young basalts. “Apparent exposure ages” can also be calculated for features that have experienced some erosion, yielding a lower limit for the true age. Sites where a steady state between cosmogenic nuclide production and erosion is interpreted to have been reached can be used to determine a mean erosion rate. Radiogenic production of Ar can be used to determine crystallization ages of basalts and He production from U and Th can be applied similarly.
Noble gas concentrations are a function of production rate, time, and retentivity. Present day Martian cosmogenic production rates have been estimated from modeling based on measurements taken on meteorites and the moon. Hayden Miller and I are currently performing a series of diffusion experiments on mineral phases expected at Gale Crater to determine light noble gas retentivity.
Upon landing, all noble gas measurements will be performed by the Sample Analysis at Mars (SAM) suite onboard the MSL rover. Solid sample will be transferred to SAM, thermally released, purified, and analyzed in static mode on the quadrupole mass spectrometer. The APXS instrument will provide bulk composition data where needed. In addition, we have been using the Pfeiffer Prisma quadupole at Caltech to cross check the capabilities of SAM.