Rock samples from the floor of Jezero Crater show significant contact with water along with possible organic compounds.

Rock samples from the floor of Jezero Crater show significant contact with water along with possible organic compounds.
Rock samples from the floor of Jezero Crater show significant contact with water along with possible organic compounds.

Analysis of multiple rocks found at the bottom of Jezero crater on Mars, where the Perseverance rover landed in 2020, reveals a significant interaction between rocks and liquid water, according to a study published Nov. 24 in Science. Those rocks also contain evidence consistent with the presence of organic compounds.

The existence of organic compounds (chemical compounds with carbon-hydrogen bonds) is not direct evidence of life, since these compounds can be created through non-biological processes.

Perseverance previously found organic compounds in the Jezero Delta. Deltas are fan-shaped geological formations created at the intersection of a river and a lake at the crater rim. Scientists on the Mars 2020 mission were particularly interested in the Jezero Delta because such formations are created when a river carrying fine-grained sediment enters a deeper, slower-moving body of water. As the river’s water spreads, it slows down abruptly, depositing the sediment it carries and, in doing so, traps and preserves any microorganisms that may exist in the water.

However, the crater floor, where the rover landed for safety reasons before traveling to the delta, was more of a mystery. In lake beds, one expects to find sedimentary rocks, because the water deposits layer after layer of sediment. However, when the rover landed there and looked around, some researchers were surprised to notice igneous rocks (which is cooled magma) on the crater floor with minerals that recorded not only igneous processes but significant contact with water.

“The nature of the interaction of water with igneous rocks is very intriguing and chemically unique. There are carbonates, which require CO2 dissolved in water to form. There are also fascinating combinations of materials like sulfate and perchlorate, probably formed through the evaporation of water,” says Eva Scheller (PhD ’22), now a postdoctoral fellow at MIT. Scheller, the corresponding author of the Science article, conducted this investigation on the floor of Jezero crater during her PhD work at Caltech.

Signs of different types of salts, including carbonates, sulfates, and perchlorates, along with possible co-located organics, were discovered using SHERLOC, or the Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals instrument. Mounted on the rover’s robotic arm, SHERLOC is equipped with a number of tools, including a Raman spectrometer that uses a specific type of fluorescence to search for organic compounds and also see how they are distributed in a material, giving insight into how they were preserved. . in that place.

Perseverance on Mars sample collection. This mosaic of images was acquired by the WATSON camera on the rover’s robotic arm. Rock cores from the two holes (arrow) were drilled into an igneous rock of the Máaz formation. The 6 cm long, 1.3 cm diameter cores were sealed in individual sample tubes and are now stored inside the rover.

“SHERLOC’s microscopic composition imaging capabilities have really opened up our ability to decipher the temporal order of Mars’ past environments,” says Sciencepaper co-author Bethany Ehlmann, professor of planetary science and associate director at the Keck Institute. for Spatial Studies. “Microscopic fingerprints show that igneous rocks formed and then water circulated through them, altering the rocks and depositing minerals in voids and crevices. In some locations, the data shows evidence of organic compounds within these potentially habitable niches.”

As the rover moved toward the delta, it took several samples of the water-altered igneous rocks and stored them for a possible future sample-return mission. Definitively determining the nature of past moist environments, the presence and type of organic compounds, and whether these have anything to do with life, requires returning samples to Earth for examination in laboratories with advanced instrumentation.

“These will be key samples for understanding the environments on ancient Mars and whether they had conditions suitable for life or even harbored life,” says Scheller.

The Science article has numerous co-authors from multiple institutions around the world. This research was funded by NASA, the European Research Council, the Swedish National Space Agency, and the UK Space Agency.

Aqueously sampled altered igneous rocks on the floor of Jezero Crater, MarsSciences


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