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The Perseverance rover of the Mars 2020 mission has been exploring Jezero Crater since February 2021. His role? Collect and prepare Martian soil samples to be recovered on a later mission and then carefully examined on Earth for possible traces of ancient life. Data transmitted by the rover during the first in situ analysis shows that several of the crater’s rocks contain signs of liquid water and possible organic compounds.
Jezero Crater was chosen as the landing site because several surveys and orbital observations indicated that it contained a lake about 3.5 billion years ago; therefore, its soil probably contains traces of ancient life forms. During its mission, the rover has already detected traces of organic compounds in the sediments of the delta, located on the edge of the crater – a geological formation formed as a result of the intersection of an ancient river and lake. On the other hand, the nature of the crater floor greatly surprised scientists when the rover landed.
While the team expected to find sedimentary rocks deposited layer by layer by the lake waters, it turned out that the crater floor is composed mainly of volcanic rocks containing minerals, evidence not only of magmatic processes, but also of important interactions with liquid water. Indeed, the presence of carbonates and other salts in these rocks is possible only if the water has previously perforated and dug furrows in these rocks. After analysis, it turns out that some of them show traces of organic matter.
Two periods of water-related activity
The Perseverance rover has several instruments on board to carry out its mission, including the SHERLOC spectrometer (scanning habitable environments using Raman scattering and luminescence of organic and chemical substances), which allows even more precise analysis of rock fragments using Raman spectroscopy based on small-scale imaging and ultraviolet laser. It was thanks to him that Caltech researchers discovered the presence of minerals and possible organic compounds in three rocks taken from two different parts of the crater. The results of their study have just been published in the journal Science.
The SHERLOC data shows that igneous rocks formed and then water flowed through them, weathering the rocks and depositing minerals in crevices and fissures created by erosion. “The nature of the interaction of water with igneous rocks is very intriguing and chemically unique. There are carbonates that require CO2 dissolved in water to form. There are also interesting combinations of materials such as sulfate and perchlorate, which are likely formed when water evaporates, ”says Eva Scheller, a research fellow at the Massachusetts Institute of Technology and the first author of the study.
The team says they have found evidence for two different ancient water environments from different eras. This confirms the results of a 2015 study by researchers at Brown University, which identified at least two periods of water-related activity in the history of Mars. Scheller and his collaborators now state that all of the rocks analyzed by SHERLOC contain “aromatically compatible” fluorescence signatures in minerals associated with both aquatic environments.
The long-awaited return of samples
The researchers specify that the first liquid water event, which probably occurred about 3.8 to 2.7 billion years ago, led to the formation of carbonates in olivine-rich igneous rocks. Then, much later, about 2.6 to 2.3 billion years ago, salt-rich water probably formed a sulfate-perchlorate mixture in the rocks. On the other hand, it is unlikely that another aquatic event has occurred since then, since perchlorates are readily soluble in water.
However, the team emphasizes that the presence of organic compounds (i.e., chemical compounds with carbon-hydrogen bonds) is not direct evidence of life, as these compounds can also be created by non-biological processes (including geologic or meteor impact events).
Moving towards the delta, the rover, of course, took some samples of water-weathered igneous rocks and saved them for a possible sample return mission. Only an analysis carried out on Earth using the most modern instruments will make it possible to finally determine the nature of past aquatic environments, confirm the presence and type of organic matter found in rocks. “These samples will be the key to understanding the environment of ancient Mars and whether there were conditions for life or even life,” Scheller says.
However, you will have to be patient. To date, the return of Martian samples is planned to be carried out by two space probes – one developed by NASA, the other – by the European Space Agency, the launch of which is scheduled for 2026. 2031. Meanwhile, Perseverance, having reached the edge of the delta last July, continues its mission in search of other clues. He has already collected about fifteen samples.