NASA’s Perseverance rover is collecting valuable information for scientists back on Earth. A recent study explored how laser-induced breakdown spectroscopy (LIBS) is being used to analyze the Martian surface.
The United States National Aeronautics and Space Administration (NASA) has an invested interest in learning more about Mars. The agency’s long-term goals include sending astronauts to Mars; however, before it can do so, NASA is conducting numerous experiments on the planet’s surface using rovers to learn more about it (1).
Perseverance is helping NASA to do just that. Over the past couple years, numerous studies have shown how Perseverance has used spectroscopic techniques to analyze the surface of Mars (2–4). A recent study published in Spectrochimica Acta Part B: Atomic Spectroscopy, explored the rovers SuperCam use of laser-induced breakdown spectroscopy (LIBS) technology in conducting elemental analyses on the Martian surface, even at extended distances (5). SuperCam is an instrument attached to the Perseverance rover, and its primary objective is to analyze Martian soil and rocks (5,6).
LIBS operates by directing a laser pulse at a target, creating a plasma plume that emits light (5). This emission is then analyzed to determine the elements present (5). The technique is particularly advantageous for planetary missions due to its ability to operate from a distance, minimizing the need for sample handling.
This study focused on SuperCam’s elemental calibration, which is essential in acquiring accurate data from samples. The research team investigated the potential issues that can emerge from the plasma plume and its physical variability (5). Specifically, they addressed concerns about how reduced laser irradiance at longer distances and differing material properties between rocks and soils could impact the quality of data (5).
Plasma temperatures were also explored in this study. The multiline Boltzmann plot method was used to do this. By using this method, the research team was able to determine that apparent plasma temperatures, derived from calcium (Ca I) lines, averaged 5,628 K on Mars (5). Importantly, these temperatures showed no systematic decrease with distance or significant variation between rock and soil targets (5). The variability observed in Martian plasma temperatures was entirely accounted for in SuperCam's laboratory calibration data set, confirming the reliability of its elemental measurements up to at least 8 meters away (5).
The researchers also pointed out key observations in the electron density in the samples. For example, they found that the electron density is approximately 1.4 times higher in soils than rocks (5). The researchers concluded that this variation is likely because of topographic relief on the H-α line, though this mechanism remains poorly understood (5). Although this variability poses challenges in quantifying hydrogen abundance, it does not compromise the broader elemental calibration.
The calibration ability of SuperCam allows the instrument to remain stable even when facing different plasma conditions. The difference in apparent temperatures between rocks and soils (~100 K) is significantly smaller than the standard deviation observed in homogeneous laboratory samples (±210 K) (5). This observation suggests that any fluctuations in plasma conditions are well within the range accounted for during SuperCam’s calibration process (5).
The researchers also conducted time-resolved LIBS experiments with SuperCam’s engineering qualification model (EQM) on Earth, revealing that while local thermodynamic equilibrium (LTE) is not valid for time-integrated spectra on Mars, the averaged measurements provide consistent results (5).
The importance of this study is that it shows SuperCam can effectively perform elemental analyses without significant recalibration, ensuring consistent data quality across diverse target types and distances. This is critical for future missions to Mars, where ensuring the validity of elemental data is vital for prioritizing sample collection (1,5).
This study was led by H.T. Manelski of Purdue University, and the research provides key insights into how SuperCam, aboard NASA’s Perseverance rover, maintains accurate performance despite the challenges of varying target types and distances in the harsh Martian environment (5).
