Scientists have discovered traces of three water periods in the rocks of Mars
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- Scientists have discovered traces of three water periods in the rocks of Mars
The Perseverance rover has discovered traces of at least three separate periods of interaction with water in the rocks of the Jezero crater on Mars. First, they were changed by groundwater rich in carbon dioxide, then the rocks were probably influenced by an ancient lake, and later by heated groundwater. The researchers were able to reconstruct the sequence of events based on the composition of the minerals, but they do not yet know exactly when each of them occurred. About how the history of water was preserved in Martian rocks and what the discovery says about the search for ancient life, see the "Izvestia" material.
Why the discovery surprised the researchers
In September 2023, Perseverance reached the inner edge of the Jezero crater, where there is a geological area that researchers call the Margin Unit — the marginal stratum. It stretches along the shore of the lake that existed here in the past. Therefore, scientists expected to find primarily sedimentary rocks formed by the accumulation of sand, silt and other particles at the bottom of the reservoir.
Interest in this place was reinforced by observations from orbit: spacecraft instruments found signs of carbonates here. On Earth, such minerals are often formed with the participation of water, including in lakes and shallow seas. Sedimentary deposits and carbonates are able to preserve information about the conditions in which microorganisms could once exist.
However, the rover found mostly igneous rocks in place. They occur when the molten substance cools down — underground or after an eruption to the surface. Further analysis showed that after their formation, these rocks repeatedly came into contact with water. Each such episode left its own mineral traces in them.
"Before arriving at the boundary layer, the main hypothesis was that carbonates detected from orbit were formed by the interaction of rocks with the lake in the Jezero crater," said lead author of the study, researcher at Purdue University Candice Bedford.
Now, according to her, it turned out that this territory was located at the intersection of several water systems.
How Perseverance studied the breeds
The SuperCam device mounted on the rover's mast played an important role in the work. It allows you to explore remote rock areas: analyze the light reflected by them, as well as direct a laser to the surface. The laser pulse affects a small area at a distance of up to 6.5 m, after which the device studies the light of the formed plasma. The chemical composition of the material can be determined by its spectrum.
In this way, Perseverance investigated more than 185 bedrock sites in the marginal stratum. The rover also studied their appearance and relative position. This made it possible to compare rocks at different heights and trace which changes are related to water and which relate to their initial formation.
The elevation difference on the studied route was about 265 m. Above were coarse—grained crystalline rocks rich in olivine, a mineral containing magnesium and iron. There were almost no signs of water exposure in them. Scientists attribute their origin to magma, which slowly cooled under the surface of Mars: during this time, the crystals managed to grow relatively large. Later, the overlying rocks collapsed, exposing this area.
Below, closer to the ancient bottom of the lake, the rocks looked different. The olivine grains turned out to be cracked, and silica was found between them. The difference between the upper and lower sections was one of the evidences that the water changed the original igneous rock after its formation.
The first period: water penetrated underground
According to the researchers, the first episode they identified was the impact of groundwater rich in carbon dioxide. They penetrated the cracks and reacted with olivine. As a result, carbonates formed, which filled part of the fractures in the rock.
Today, these mineral-filled cracks look like protruding ridges. The surrounding material deteriorated faster over time, so more stable areas became visible on the surface. Such structures were found at relatively low elevations of the studied territory.
Carbonates are important for reconstructing the history of water: their composition and location help us understand where the fluids passed through and how they interacted with the rock. But the presence of carbonates alone does not indicate the existence of life. They can form as a result of common geological and chemical processes.
The second period: the possible influence of the lake
The researchers attribute the next episode to the conditions that existed in the crater after the first rock change. It could be associated with an ancient lake — the authors formulate this part of the story more carefully, since mineral traces do not allow us to unambiguously identify the source of the water.
One of the clues was silica. It was found in a part of the rocks located below the proposed coastline. Co-author of the study, planetary scientist at the University of Hawaii at Manoa Eleni Ravanis explained that when olivine is converted into carbonates, silica may remain in the rock. In the samples below the water level, it turned out to be more.
Thus, the carbonates found did not necessarily arise as a result of a single process. Some of the changes could be related to groundwater, and some to the later interaction of rocks with lake or associated water. That is why the initial explanation, based solely on orbital observations, proved insufficient.
The third period: heated water passed through the rocks
The latest of the three identified episodes left traces in the eastern part of the marginal stratum. There Perseverance found mineral veins about 25 cm thick. In particular, calcium sulfate and fluorite were found in their composition.
Fluorite is particularly interesting to scientists. Its appearance in such a geological context indicates the circulation of heated water through rocks. Researchers consider these veins to be evidence of a later period of groundwater activity, which differed from the previous ones in terms of conditions.
The minerals and their location allow us to establish the relative order of events: which changes occurred earlier and which overlapped with them later. However, according to the available data, scientists have not yet been able to determine their exact age. It is also unknown how long each water period lasted and what intervals separated them.
What does this mean for the search for life on Mars?
On Earth, the interaction of water with olivine can, under certain conditions, be accompanied by the release of hydrogen. Some microorganisms are able to use it as an energy source. Carbonates and silica, in turn, are of interest as minerals that may contain traces of pre-existing microbial life.
Therefore, the discovery expands the understanding of the environments that could exist in the Jezero crater. Judging by the rocks studied, its history was not limited to one lake: water also moved underground, reacted with igneous rock, and later circulated in a heated state. At the same time, this study did not find any evidence of life. It describes the geological conditions that are important for its search.
Bedford noted that the results obtained directly on the surface of Mars often change the picture formed by the orbital data. According to her, studying the marginal stratum will help clarify the history of water not only in the Jezero crater: it is located inside one of the largest areas of carbonates on the planet. The next question for researchers is how different water systems were related to climate changes on early Mars and the possibility of habitable conditions.
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