Using Raman Spectroscopy to Detect Life on Mars

For Raman spectroscopy to be an effective technique for detecting bioorganic molecules on Mars, adjustments need to be made to the laser power settings of Raman instruments, according to a new study published in Icarus by scientists from the University of Science and Technology of China (1). These adjustments in laser power, the authors of the study argue, are critical for Raman instruments used by Mars rovers, because they allow researchers to detect and identify more bioorganic molecules (1). This is important for detecting the possibility of life and life conditions on the Red Planet.

Extremely detailed and realistic high resolution 3D image of Planet Mars. Shot from outer space. Elements of this image are furnished by NASA. Image Credit: © Sasa Kadrijevic - stock.adobe.com

Mars is the fourth planet from the Sun in the Milky Way galaxy. The exploration of Mars is ongoing, and studying the planet has been a fascination for many scientists for several reasons (2–5). Because water molecules as well as bioorganic molecules have been found on the planet, the scientific consensus has theorized that some conditions for life could be found on the planet. Among the various indicators of life, bioorganic molecules such as lipids and amino acids are particularly significant because of their ability to persist in the geological record over extensive periods (1).

Because Raman spectroscopy is a molecular spectroscopic technique, it can study and measure the vibration of molecules. However, the effectiveness of Raman spectroscopy heavily depends on the laser power settings (1). If these settings are not optimized, the researchers would be unable to obtain the data they can from the instrument, because either the samples would be damaged or scientists would receive weak signals, rendering the data uninterpretable (1).

In this study, Gen-Tao Zhou and colleagues explored how to tinker with the laser settings of Raman instruments to study lipids and amino acids better. In their analysis, the research team studied lipids, such as decanol, hexadecane, and palmitic acid, and amino acids, such as alanine, aspartic acid, glycine, histidine, and tyrosine, to determine the optimal laser power for organic detection. The research involved varying the Raman laser power from as low as 1% (0.63 ± 0.01 mW) to as high as 100% (66.40 ± 1.85 mW) within the operational range of Raman payloads on Mars rovers (1).

The findings revealed that the laser power has a significant impact on the Raman spectra of organic samples. With high-powered lasers, lipid samples were damaged (1). The damaged lipids showed that the spectral characteristics were drastically altered, which means the spectra data was not usable (1).

It was a different story with amino acids. Unlike lipids, amino acids were able to withstand high-power lasers, showcasing great stability. However, the researchers discovered that amino acids could not be studied using low-power lasers because the Raman signals were reduced (1).

The accuracy of Raman spectral data is important in scientific research. Not having accurate data could lead to false conclusions, compromising the validity of the scientific research conducted. With their study, the researchers have compiled a laser power-based spectral library, which will be invaluable for future Mars missions (1). This library includes detailed spectral data, allowing for comparisons with future in situ and orbital measurements on Mars (1).

By optimizing the Raman laser power settings, scientists can enhance their ability to detect and identify bioorganic molecules on Mars, bringing us closer to answering the age-old question of whether life ever existed on the Red Planet (1). The careful balance of laser power ensures that the fragile clues to life’s existence are not destroyed in the process of discovery.

References

(1) Liu, W.-P.; Yin, W.; Hu, Q.-T.; et al. Effect of Laser Power on Raman Analyses of Lipids and Amino Acids: Implications for Extraterrestrial Life Exploration. Icarus 2024, 412, 115986. DOI: 10.1016/j.icarus.2024.115986

(2) Wetzel, W. Raman Spectroscopy and its Role in Perseverance Rover’s SuperCam Instrument. Spectroscopy. Available at: https://www.spectroscopyonline.com/view/raman-spectroscopy-and-its-role-in-perseverance-rover-s-supercam-instrument (accessed 2024-07-21).

(3) Spectroscopy Staff, SHERLOC’s Precision Unveiled: Calibration Method Enhances Raman Spectroscopy on Mars. Spectroscopy. Available at: https://www.spectroscopyonline.com/view/sherloc-s-precision-unveiled-calibration-method-enhances-raman-spectroscopy-on-mars (accessed 2024-07-21).

(4) Workman, Jr. Mars Rover Uses Spectroscopy to Detect Diverse Organic-Mineral Associations in Jezero Crater. Spectroscopy. Available at: https://www.spectroscopyonline.com/view/mars-rover-uses-spectroscopy-to-detect-diverse-organic-mineral-associations-in-jezero-crater (accessed 2024-07-21).

(5) Spectroscopy Staff, Analyzing Geological Targets Using Laser-Induced Sparks on Mars. Spectroscopy. Available at: https://www.spectroscopyonline.com/view/analyzing-geological-targets-using-laser-induced-sparks-on-mars (accessed 2024-07-21).