Improving Sulfur Detection in Martian Targets with time-resolved LIBS

Abstract

The first extraterrestrially employed LIBS instrument is ChemCam on NASA’s Mars rover Curiosity, which has been successfully analyzing materials on the martian surface since the rover’s landing in August 2012 [1,2]. The success of ChemCam has led to the selection of the SuperCam instrument [3] for NASA’s upcoming Mars2020 rover mission. As for ChemCam, SuperCam will have a LIBS telescopic system combined with a high-resolution color remote micro-imager cam-era [4] for remote analysis, along with the added capabilities of complementary Raman spectroscopy, time-resolved fluorescence spectroscopy, and visible and infrared reflectance spectroscopy [5,6]. Time-resolved Raman spectroscopy will be done with the same spectrometer and detector that are used for the third wavelength range for LIBS, providing the possibility of also recording time-resolved LIBS data in a wavelength range of 536 – 853 nm. The detection of S in ChemCam data, which falls in this range, is challenging, in particular when samples with high Fe are analyzed. As the S emission is ionic and the superimposed Fe lines are mainly neutral, their emission occurs in different temporal regimes, which can be utilized for their differentiation with time-resolved LIBS. Here, we present studies on Fe-Sulfate, Pyrite, and Pyrrhotite measured in martian atmospheric conditions where we explore the S and Fe typical emission behaviors and develop strategies for improved S detection in martian targets. All data was taken at the LIBS set-up at DLR Berlin in simulated martian atmospheric conditions (7 mbar) with a high resolution (14-96 pm) Echelle spectrometer (Aryelle Butterfly, LTB Berlin) covering continuously 270-850 nm with an intensified CCD and a Nd:YAG laser (1064 nm, 8 ns, 10 Hz).