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Before Perseverance landed in Jezero de Mars crater in February 2021, scientists’ understanding of the crater was shaped by observations of spacecraft, such as the Mars Express satellite and Mars Reconnaissance Orbiter. But now, with an operational robot messing its wheels on the ground, an interdisciplinary team of geologists and planetologists have been able to make better assessments of the region’s ancient and aquatic past. Since Perseverance’s main mission is to look for signs of fossilized life, this new information will be crucial in deciding where to look.
There is no stable liquid water on the surface of Mars today – it is a very cold and very dry world – but in its ancient past the planet was warmer and wetter. The 28-mile-wide Jezero Crater was once a lake, and although the water is long gone, evidence of that water and the way it flowed is lodged in the rock. The team’s recent paper, published today in Science, describes rocks that may contain geological evidence of the Martian interior. It also details new measurements taken from a mound dubbed Kodiak, which give clues to a environment.
“The results are twofold,” said Nicolas Mangold, planetologist at the University of Nantes in France and lead author of the new article. “First, the Kodiak stratigraphy indicates a past lake but slightly different from expectations, and second, the presence of rock deposits at the top of the delta is the most surprising and unexpected find, as these rocks are not expected to occur in a delta lake system, ”he wrote in an email to Gizmodo.
Researchers have reported over 300 boulders and pebbles; the largest boulders were almost 5 feet in diameter. The rocks are ancient igneous rocks that may have broken off the rim of the crater or carried into Jezero by a river flowing into it, Mangold said, adding that the rocks came from flooding, events that could be linked to a change from the old Martian climate. Previous search indicated great flooding on Mars but in Gale crater, where the Curiosity rover plies its trade.
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Ken Farley, a scientist on the Perseverance Project at Caltech and co-author of the recent article, described the complexity of the Lake Jezero system at a NASA press conference in July:
“One of the hypotheses that we are trying to test is that the lake that once filled Jezero was not there just once, but has gone through several episodes of filling, draining and re-filling.” , said Farley. “This is very important because it means that we will have several periods during which we could possibly learn more about the environmental conditions on Mars, and we will have several periods where we could search for ancient life that could have existed on the planet. “
Whether the Jezero flooding was part of the lake’s behavior or one of the last hydrologic activities in the area before it dried up, researchers don’t yet know. What they determined was that the level of Lake Jezero was about 328 feet lower than previously thought based on orbital observations. The Perseverance landing site is at the western end of Jezero, and the rover moved west from there, to investigate a fan delta at the edge of the crater.
The rover “was already ready to reach and cross the fan,” Mangold said, “but now we’ll be paying more attention to the lower layers where the lake deposits are likely to be, and the higher deposits to analyze the rover. unit rich in rocks, and better understand this transition in hydrology.
Perhaps Perseverance’s biggest task is to research and collect evidence of biosignatures, whatever microbial life from Mars’ ancient past may have left behind. Some of the strata analyzed by the team are called “low end” (because it is the substance that has settled at the bottom of a waterlogged Jezero). These finer-grained clays eventually lithified, and it’s their soft geology that leads the team to believe it’s a good place to search for fossils.
The expectation is that these fossils, if they exist, would look a lot like that of Earth stromatolites, which are fossilized microbial mats created by bacteria. In this way, fossils should be seen more as traces of fossils; these are things created and left by long-the extinct creatures, not the fossil ones creatures themselves. Perseverance is equipped with instruments specially designed for this research.
“In my opinion, the identification of biosignatures, which, if present, should be microbial and small-scale in origin, will depend on the high-resolution observations made with the WATSON, SHERLOC and PIXL instruments once the rover s ‘approaching the delta,’ Keyron Hickman-Lewis, a paleontologist at the Natural History Museum in London and co-author of the new study, said in an email. “Certain microbial structures (eg, microbial carpet tissues) and biological organic materials (biomolecules) must be identifiable if they are present and preserved. “
To take a step back, it is surprising that Perseverance (and its human team!) Have discerned so much on the the story of Jezero already, and its implications for possible astrobiology, simply from images of the rock formations in the crater. Whether or not biosignatures are found during this mission, think about what scientists will be able to do when, if all goes well, Martian samples arrive on Earth in the early 2030s. It will be a brave new world, nestled within test tubes.
More: Perseverance carved out two Martian rocks that may be volcanic and shaped by water
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