NASA-гийн Perseverance хөлөг Ангараг гарагийн гадаргуу дээр усны нөлөөгөөр гурван өөр үе шаттайгаар өөрчлөгдсөн чулуулгуудыг илрүүлснээр эртний нуурын тухай хялбаршуулсан онолыг няцаав.
NASA-гийн Perseverance ровер Жизеро тогооны “Margin Unit” бүсэд судалгаа хийхдээ тойрог замын өгөгдлөөр таамаглаж байсан энгийн тунамал чулуулгийн оронд магмын гаралтай чулуулгуудыг илрүүлжээ. Эрдэмтдийн баг SuperCam багажийн тусламжтайгаар 185 гаруй цэгт лазераар шинжилгээ хийсний дүнд тус бүс нутаг нь усны нөлөөлөлд олон удаа өртсөн “усан системийн уулзвар” болохыг тогтоосон байна.
Судалгааны тэргүүлэх зохиогч, Пурдугийн их сургуулийн судлаач Кэндис Бэдфордын тайлбарласнаар, эхний ээлжид нүүрстөрөгчийн давхар ислээр баялаг гүний ус чулуулгийн ан цаваар дамжин карбонатлаг эрдэс үүсгэсэн байна. Дараагийн шатанд тус тогоонд байсан эртний нуурын ус чулуулгийг дахин өөрчилсөн бол гурав дахь үе шатанд халуун ус газар доогуур эргэлдэж, кальцийн сульфат болон флюорит агуулсан судал үүсгэжээ.
Энэхүү олон давхаргат үйл явц нь тус бүс нутаг зөвхөн нэг нуурын нөлөөгөөр бүрэлдээгүйг харуулж байна. Эрдэмтэд карбонат болон цахиурын нэгдлүүд нь бичил биетний амьдрах орчин байсан эсэхийг тодруулах, Ангараг гарагийн уур амьсгалын түүхийг дахин судлахад чухал ач холбогдолтой гэж үзэж байна.
Дэлгэрэнгүйг эх сурвалжаас харах
↓Эх сурвалжийг нээх ↓
NASA’s Perseverance rover has found evidence that the same part of Jezero Crater was changed by water at least three different times. What first looked like a simple ancient lakeshore now appears to have been shaped by groundwater, lake water and, later, hot fluids moving underground.
Scientists had expected the crater’s Margin Unit to contain sedimentary rocks left behind by the lake that once filled Jezero. Orbital data had also shown strong signatures of carbonate minerals there, which seemed to fit that picture.
But once Perseverance arrived in the area, the rocks told a different story. NASA’s Jet Propulsion Laboratory reports that the rover found igneous rocks instead, with signs of several separate phases of water alteration.
A Longer History in the Rocks
A lot of the evidence came from SuperCam, the instrument mounted on Perseverance’s mast. As reported by the study, published in Communications Earth & Environment, this can fire a laser at rocks from up to 21 feet, or 6.5 meters away.
The laser creates a tiny burst of plasma, and scientists can study its spectrum to work out what the rock is made of. Perseverance used SuperCam on more than 185 bedrock targets across the Margin Unit.
“Before we arrived at the Margin Unit, the main hypothesis — derived from orbital observations — was that the carbonate seen from orbit formed from interaction with the lake that existed in Jezero Crater,” said Candice Bedford, a research scientist at Purdue University and lead author of the study.
That idea did not fully match what the rover found on the ground. Bedford said the area turned out to be “a sort of crossroads for aqueous systems.” Across about 870 feet, or 265 meters, of elevation, the rover found very different kinds of rock. Higher up, Perseverance came across coarse, crystalline material rich in olivine, with almost no sign that water had changed it.
Researchers concluded that this rock formed inside magma below the Martian surface, then became exposed later through erosion.
The Lake May Have Changed the Rocks Again
Closer to the ancient lakebed, the picture changed. The olivine there was much more altered. Its grains were fractured, and silica had filled spaces between them. The team identified the first known episode as one involving groundwater rich in carbon dioxide. As that water moved through the rock, it reacted with olivine and formed carbonate inside cracks, mainly at lower elevations.
Later erosion removed some of the softer material around those cracks, leaving the harder carbonate-filled parts standing out as ridges. A second episode may have been connected to the lake itself.
“Some of the Margin Unit rocks also contain silica,” said Eleni Ravanis, a planetary scientist at the University of Hawaii at Manoa and a coauthor of the study. “Turning olivine into carbonate can leave silica behind, and we see more of that silica in rocks that sat below the water line.”
The research team notes that carbonate and silica are interesting because, on Earth, reactions between water and olivine can produce hydrogen that some microbes use as an energy source. Those minerals can also preserve traces left behind by past microbial activity.
Hot Water Came Later
The third episode looks different again. In the eastern part of the Margin Unit, Perseverance found mineral veins about 10 inches, or 25 centimeters, thick. These veins contain calcium sulfate and fluorite. Fluorite matters because it commonly forms when hot water moves through volcanic rock.
For the researchers, its presence points to a later period when heated groundwater circulated below the surface, after the earlier groundwater and lake-related activity. The result is a much more layered picture of Jezero Crater than scientists had expected. The Margin Unit was not shaped by one lake alone. The same rocks were changed several times, under different conditions, by different types of water.
“If there is one thing I have learned after 10 years working with Mars rovers, it is that Mars constantly throws surprises at you,” Bedford said.
She noted that the discovery could push researchers to revisit how water shaped Jezero Crater, and to better piece together how Mars’ climate and potential for life evolved.
“It is very rare that things are as we expect them to be from orbital data. I hope this work helps reshape how scientists view the history of water in Jezero Crater and across Mars.”
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