NASA’s Perseverance rover has provided new insight into the presence of organic molecules on Mars, at the same time shedding more light on the watery history of our now-arid neighbor. The rover’s instruments, designed to detect organics in rock minerals, has sent back fluorescence and Raman data that, together with X-ray fluorescence and camera data, indicates the existence of one- and two-ring aromatics intimately associated with minerals. Water may also have played a role in the way these molecules were deposited .
Sediments: A Rich Source of Organics
It has been more than two years since the Perseverance rover landed safely in Jezero crater, a prominent geological feature in the northern hemisphere of Mars, in February 2021. Jezero crater was chosen as the landing site because it is believed to have once contained a lake into which rivers flowed and deposited sediments about 3 billion years ago. If microbial life once existed on Mars, these sediments would be a prime candidate for finding its organic traces. Perseverance was designed specifically to search for these races in Martian soil and rocks.
In addition to cameras, a weather station, an X-ray fluorescence spectrometer, a drill and a sandblaster, and even a small helicopter, the rover is home to SHERLOC (Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals). This dual spectrometer scans its target with a deep ultraviolet (DUV) laser beam and simultaneously detects fluorescence photons in the 253 to 355 nm range, as well as Raman scattering in the 700 to 4000 cm–1 range. Two integrated cameras provide high-resolution images and spatial context for the detected features.
Rocks of the Lake Floor
Perseverance spent its first year analyzing rocks on the crater floor, thought to have been a lake in Mars’ past. The initial results from these rocks surprised the researchers: they were clearly of igneous rather than sedimentary origin . However, SHERLOC also detected organic material within the minerals that appeared to have been altered by water.
The second set of analyses provides a deeper insight. It included ten new sites, some of which are up to several hundred meters away from each other and from the landing site, covering two different geological formations. In these samples, the researchers were able to identify for the first time different types of organic matter associated with specific minerals.
Aromatics within or around Hydrated Crystals
Fluorescence features revealed four groups of organic molecules, characterized by being either a doublet or rather a broad peak, and the maximum wavelength. Together with Raman spectra, X-ray fluorescence data, and textural details of the rocks revealed by the cameras, the researchers concluded that the rocks contain one- or two-ring aromatic molecules that are either embedded in or more loosely associated with water-altered minerals such as hydrated sulfate crystals.
Organic matter has been detected by several previous missions, including the Curiosity rover, which found organic signatures in Martian soil and dust ten years ago. Investigations of Martian meteorites on Earth have also indicated the presence of organic molecules. Perseverance has now shown that organic molecules and water-altered rocks share both location and a common past.
The Significance of Organics in Water-Altered Minerals
If there was life on Mars, microorganisms would have lived in water, and their organic remains would have been trapped in sediments and rocks. Still, the researchers remain cautious about the possibility of a biotic origin for the structures analyzed. “The general spatial correlation … suggests that organic molecules may have been abiotically aqueously deposited or synthesized within these altered volcanic materials on the crater floor,” they say.
Further details about Martian minerals and their associated organic molecules can only be revealed with Earth-bound technology. Perseverance has already collected a number of physical samples from various locations and continues to do so while traveling through the delta, which appears to be full of interesting sedimentary rocks. Each sample is sealed in a test tube and tucked up inside the rover. Some tubes will also be left behind at designated spots on the Martian soil to have a backup, in case something happens to the rover. NASA–ESA’s Mars Sample Return mission is scheduled for launch in 2027, returning the samples to Earth in 2033.
 Sunanda Sharma, Ryan D. Roppel, Ashley E. Murphy, Luther W. Beegle, Rohit Bhartia, Andrew Steele, Joseph Razzell Hollis, Sandra Siljeström, Francis M. McCubbin, Sanford A. Asher, William J. Abbey, Abigail C. Allwood, Eve L. Berger, Benjamin L. Bleefeld, Aaron S. Burton, Sergei V. Bykov, Emily L. Cardarelli, Pamela G. Conrad, Andrea Corpolongo, Andrew D. Czaja, Lauren P. DeFlores, Kenneth Edgett, Kenneth A. Farley, Teresa Fornaro, Allison C. Fox, Marc D. Fries, David Harker, Keyron Hickman-Lewis, Joshua Huggett, Samara Imbeah, Ryan S. Jakubek, Linda C. Kah, Carina Lee, Yang Liu, Angela Magee, Michelle Minitti, Kelsey R. Moore, Alyssa Pascuzzo, Carolina Rodriguez Sanchez-Vahamonde, Eva L. Scheller, Svetlana Shkolyar, Kathryn M. Stack, Kim Steadman, Michael Tuite, Kyle Uckert, Alyssa Werynski, Roger C. Wiens, Amy J. Williams, Katherine Winchell, Megan R. Kennedy, Anastasia Yanchilina, Diverse organic-mineral associations in Jezero crater, Mars, Nature 2023, 619, 724–732. https://doi.org/10.1038/s41586-023-06143-z
 Eva L. Scheller, Joseph Razzell Hollis, Emily L. Cardarelli, Andrew Steele, Luther W Beegle, Rohit Bhartia, Pamela Conrad, Kyle Uckert, Sunanda Sharma, Bethany L Ehlmann, William J Abbey, Sanford A. Asher, Kathleen C. Benison Eve L. Berger, Olivier Beyssac, Benjamin L Bleefeld, Tanja Bosak, Adrian J Brown, Aaron S Burton, Sergei V. Bykov, Ed Cloutis, Alberto G. Fairén, Lauren DeFlores, Kenneth A Farley, Deidra M Fey, Teresa Fornaro, Allison C. Fox, Marc Fries, Keyron Hickman-Lewis, William F. Hug, Joshua E. Huggett, Samara Imbeah, Ryan S Jakubek, Linda C. Kah, Peter Kelemen, Megan R Kennedy, Tanya Kizovski, Carina Lee, Yang Liu, Lucia Mandon, Francis M. McCubbin, Kelsey R. Moore, Brian E. Nixon, Jorge I Núñez, Carolina Rodriguez Sanchez-Vahamonde , Ryan D. Roppel, Mitchell Schulte, Mark A. Sephton, Shiv K. Sharma, Sandra Siljeström, Svetlana Shkolyar, David L Shuster, Justin I. Simon, Rebecca J. Smith, Kathryn M. Stack, Kim Steadman, Benjamin P. Weiss, Alyssa Werynski, Amy J Williams, Roger C. Wiens, Kenneth H. Williford, Kathrine Winchell, Brittan Wogsland, Anastasia Yanchilina, Rachel Yingling, Maria-Paz Zorzano, Aqueous alteration processes and implications for organic geochemistry in jezero crater, Mars, Science 2022, 378, 1105–1110. https://doi.org/10.1126/science.abo5204
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