How NASA’s Perseverance Rover is Using Spectroscopy to Uncover the Secrets of Mars

On a clear night, in a sparsely populated area, you might be able to stare up at the night sky with nothing but a cool breeze brushing past. Amongst this backdrop you may see many lights and shapes, but under the right conditions, you may spot a point of light in the sky emitting an orange-yellow glow.

That point of glowing light is Mars, the fourth planet in our solar system.

That small glowing red light in the sky is a pinprick among the other celestial bodies that dot the nighttime sky, but its importance—and the role it may play in preserving human flourishing hundreds of years from now—is often downplayed. Because of other competing priorities, as well as wavering interest in outer space over the years, scientists continue to collect data from Mars, but we are no closer to learning all we can about it, let along landing a manned space craft on its surface.

Currently, scientists from the National Aeronautics and Space Administration (NASA) are conducting several tests on the Martian surface using the Perseverance rover. The Perseverance rover was launched in July 2020 as part of a planned mission to learn more about Mars that could help lead to further missions, including sending astronauts to the planet (1). The goal of this active mission is to investigate potential signs of ancient life and collect rock samples (1). At the beginning of the mission, one of the critical decisions NASA made was to select the landing site of Perseverance, and they chose Jezero Crater.

Mars rover navigates rocky martian landscape at sunrise, desolate terrain and rover's advanced technology, capturing essence of space exploration and discovery. | Image Credit: © ugguggu - stock.adobe.com.

The Perseverance uses spectroscopy techniques like laser-induced breakdown spectroscopy (LIBS) and Raman spectroscopy, both of which is utilized by the SuperCam integrated into the rover. These techniques have enabled Perseverance to perform detailed analyses of Martian geology and search for signs of past life.

Mars may help us to learn more about the mysteries of the solar system. Its similarities to Earth, such as the presence of water ice, seasonal weather patterns, and geological features like volcanoes and canyons, make it a prime candidate for understanding planetary evolution and habitability (2). The quest to discover microbial life, past or present, on Mars could revolutionize our understanding of life's existence beyond Earth. Research on Mars also enhances our technological capabilities, driving innovations in space exploration, robotics, and remote sensing (3). Scientists are dedicating significant time and resources to unravel the secrets of Mars, driven by the quest for knowledge and the potential benefits for humanity's future.

Front View of Planet Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System. | Image Credit: © Marshal - stock.adobe.com

Latest Studies on Mars’ Jezero Crater and The Role of Spectroscopy

The Jezero crater is a Martian crater near the planet’s equator. Back in 2005, Caleb Fassett, then a Brown University graduate student who now serves as a professor at Mount Holyoke College, identified an ancient lake in the Jezero crater, supplied by two channels on its northern and western sides (4). This discovery led to significant interest in studying the crater for signs of life. Earlier studies concluded that water from the lake eventually flowed out through a large channel on the southern side (4). This system likely dried out around 3.5 to 3.8 billion years ago (4).

The Jezero Crater was selected as the landing spot for the Perseverance rover for a few key reasons. The crater was once home to an ancient river delta, and it is believed that life could have potentially existed here (1,5). Scientists have seen evidence that water in the Jezero Crater transported minerals from the surrounding area into the crater (1). The Jezero crater is 2,300 miles from the Curiosity rover that NASA also launched years ago, so it was important that NASA chose a site far enough from the previous landing spot to collect new data (1).

Over the past few years, the Perseverance rover has been collecting data to help scientists understand more about Mars and the formation of life conditions. To extrapolate, analyze, and collect the data, spectroscopic techniques have played a key role in helping NASA accomplish its mission objectives.

One study that the Perseverance rover was involved with on Mars was exploring organic mineral associations in the Máaz and Séítah formations (5). This study, published in Nature by Sunanda Sharma and Ryan D. Roppel from the Jet Propulsion Laboratory at Caltech, highlights significant discoveries from the Perseverance rover's exploration of Jezero crater on Mars (6). These formations discovered in Máaz and Séítah were rich in pyroxene, plagioclase, and olivine.

The scientists were able to conclude that favorable conditions for preserving organic materials and potential biosignatures existed here (5,6). Using Raman and fluorescence spectroscopy, the team identified aromatic organic molecules associated with minerals linked to aqueous processes, suggesting these processes' roles in organic synthesis and preservation (6).

A common theme throughout the Perseverance mission is that Raman spectroscopy is a valuable technique that has played a crucial role in many experiments the rover is conducting particularly when it comes to mineral analysis. Another study published in Scientific Reports used Raman spectroscopy to study the mineral alteration on Mars (7,8).

Using the Perseverance rover's SuperCam instrument, researchers monitored a synthetic apatite sample over 950 Martian days, observing a decline in the Raman signal, indicative of changes in the mineral's electronic structure because of Martian environmental exposure (7,8). Laboratory simulations confirmed that UV radiation on Mars induced electronic defects in the mineral. This rapid alteration, occurring within weeks, necessitates careful interpretation of Raman spectroscopy data from Mars missions (7,8). The findings underscore the importance of continuous instrument calibration to account for environmental impacts, ensuring accurate data analysis for future planetary exploration.

Another study examined a new method to calibrate Raman spectral bandwidths, which were crucial for accurate chemical analysis of Martian samples (9,10). This study modeled observed Raman bands as a convolution of a Lorentzian intrinsic Raman band and a Gaussian instrument slit function. By analyzing calibration target data, the researchers determined SHERLOC's slit function width (34.1 cm^–1) and deconvolved it from the intrinsic Raman bandwidths (9,10). This calibration method, tested on the olivine spectra, provided clearer insights into Mars' geological history and potential habitability (9,10).

Another study looked at Perseverance’s SuperCam and how it uses laser-induced breakdown spectroscopy (LIBS) and acoustic signal detection to analyze Martian samples in the Jezero crater. This study, which took place during the first 380 sols of the mission, explored the correlation between LIBS data and acoustic signals captured by the rover’s microphone (11,12). The researchers discovered that louder and more stable acoustic signals occur when the laser interacts with compact, hard-surfaced rocks, indicating minimal loose particulate material (11,12).

Crater on planet Mars, landscape scene on the red planet | Image Credit: © dottedyeti - stock.adobe.com

The Latest Discovery

While Perseverance continues to study rocks and minerals, a recent bit of serendipity with the other rover, Curiosity, recently led to a new, and potentially fascinating, discovery that suggests where future studies on Mars may explore.

It was reported on July 20 that NASA’s Curiosity rover rolled over a few rocks on the Martian surface, crushing them and inexplicably revealing green–yellow crystals of pure sulfur (13–15). Curiosity mission deputy project scientist Abigail Fraeman told USA Today that the find was “completely unexpected” (14).

“It’s probably one of the most unusual things that we found the entire 12-year mission,” Fraeman said (14).

This discovery is significant because it was the first time scientists discovered the presence of pure sulfur on Mars. During their studies on Mars, NASA and other scientists have discovered different types of sulfur on the planet (15).

"Usually, it's coupled with oxygen and other elements that make it into a salt or something similar, but here, what we found was just chunks of pure sulfur," Fraeman said (14).

Because of this new discovery, scientists believe that this unearthing can lead to learning more about Mars’s history.

"It's telling us something new about the history of Mars and what sorts of potentially habitable environments it's sustained in the past," Fraeman said (14).

References

(1) NASA, Mars 2020: Perseverance Rover. NASA.gov. Available at: https://science.nasa.gov/mission/mars-2020-perseverance/ (accessed 2024-07-23).

(2) Talbert, T. Did Mars Ever Look Like Earth? We Asked a NASA Scientist: Episode 10. NASA. Available at: https://www.nasa.gov/solar-system/did-mars-ever-look-like-earth-we-asked-a-nasa-scientist-episode-10/ (accessed 2024-07-21).

(3) NASA, Mars Exploration Science Goals. NASA.gov. Available at: https://science.nasa.gov/planetary-science/programs/mars-exploration/science-goals/ (accessed 2024-07-23).

(4) Brown University, Ancient Martian Lake Systems Records Two Water-Related Events. Brown.edu. Available at: https://news.brown.edu/articles/2015/03/jezero (accessed 2024-07-25).

(5) 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).

(6) Sharma, S.; Roppel, R. D.; Murphy, A. E.; et al. Diverse organic-mineral associations in Jezero crater, Mars. Nature 2023, ASAP. DOI: 10.1038/s41586-023-06143-z

(7) 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).

(8) Clave, E.; Beyssac, O.; Bernard, S.; et al. Radiation-Induced Alteration of Apatite on the Surface of Mars: First In Situ Observations with SuperCam Raman Onboard Perseverance. Sci. Rep. 2024, 14, 11284. DOI: 10.1038/s41598-024-61494-5

(9) 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).

(10) Jakubek, R.S.; Bhartia, R.; Uckert, K., et al. Calibration of Raman Bandwidths on the Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) Deep Ultraviolet Raman and Fluorescence Instrument Aboard the Perseverance Rover. Appl. Spectrosc. 2023, ASAP. DOI: 10.1177/000370282312108

(11) 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).

(12) Alvarez-Llamas, C.; Laserna, J.; et al. The sound of geological targets on Mars from the absolute intensity of laser-induced sparks shock waves. Spectrochimica Acta Part B: At. Spectrosc. 2023, 205, 106687. DOI: 10.1016/j.sab.2023.106687

(13) Reilly, P. NASA’s Curiosity rover makes ‘mind-blowing’ discovery on Mars. New York Post. Available at: https://nypost.com/2024/07/20/world-news/nasas-curiosity-rover-makes-mind-blowing-discovery-on-mars/ (accessed 2024-07-21).

(14) Mayes-Osterman, C. Curiosity Rover Makes An Accidental Discovery on Mars. What the Rare Find Could Mean. USA Today. Available at: https://www.usatoday.com/story/news/nation/2024/07/22/curiosity-rover-discovers-rare-pure-mineral-mars/74495771007/ (accessed 2024-07-21).

(15) Gabriel, A. Rock Crushed by Mars Rover Reveals Crystals Never Before Seen on Red Planet. FOX Weather. Available at: https://www.foxweather.com/earth-space/discovery-pure-sulfur-mars-evidence-water (accessed 2024-07-21).