A radical change: The first recordings of a persistent Mars rover have shed new light on the climatic history of our neighboring planet. Sediments in Jezero crater confirm the presence of a crater lake from which calmly flows. But then the climate changed into violent flash floods that carried meter-sized boulders. This could document the transition from the first life-friendly days of Mars to a dry, cold climate, researchers report in the journal Science.
How convenient and abundant is the water on the red planet? This question has not yet been clearly answered. True, ancient river valleys and deltas, as well as clay minerals, indicate that Mars was once richer in water than it is today. However, it is unclear whether the water is sufficient for long-lived lakes and perhaps even the ocean, or whether it is only temporary torrents short term Heavy rain or Meltwater gave. If so, that would make early life on Mars less likely.
With perseverance eyes
now delivers Mars rover perseverance New answers to this crucial question. Because in February 2021 Crater Lake It descended – a depression about 45 kilometers wide in which a large lake could have existed until about 3.7 billion years ago. This is supported by traces of river deltas, as well as spectroscopic evidence of clay minerals and carbonate rocks by orbital probes. But whether this assumption is correct cannot be clarified from orbit alone.
For their study, Nicholas Nangold of the University of Nantes and colleagues evaluated camera recordings and multispectral images of the Mars rover, which show the western part of the crater delta. There are towering rock formations in which different layers of sediment appear. Thus, its structure and sequence allow conclusions to be drawn about the water levels in the crater lake, but also about the flow velocities of the tributaries.
Crater lake and calm river
The images reveal: Jezero crater went through two very different phases in the early days of Mars – and there was already a large lake in it. This is evidenced by fine-grained deposits in the lower sediment layers, which testify to the calming, steady, and steady flow of water. Until about 3.7 billion years ago, Jezero crater was more or less flooded.
“The rover has really answered one of the big questions – whether this crater was ever a lake,” says co-author Benjamin Weiss of NASA’s Jet Propulsion Laboratory. “Before we got there and can now confirm that, this was always in question.” The water level in Lake Jezero was at least sometimes about 100 meters lower than assumed based on orbiter data. However, the researchers see in the new data clear evidence that the climate of Mars in this early period was warm and humid enough for bodies of water.
But it did not persist in this way, as in the document perseverance recordings. The lower sediment layers of the Jezero Delta still consist mainly of fine-grained materials, as is the alluvial sands of leisurely flowing waters. Moreover, the picture changes: there are many rocks up to one meter in size and weighing several tons that are not of local origin, the researchers report.
Multispectral images of the rover show that these pieces do not consist of plate silicates and olivines like most sediments in the delta, but are dominated by low-calcium pyroxene. “The origin of these fragments must have been either the rim of Jezero crater or exposed areas of a pyroxene-rich crust 60 kilometers from Jezero crater,” the scientists say.
Shift to severe flood
But this means: the rocks weighing tons must have been carried long distances by water. “You need high-energy flash floods to remove such large, yet heavy chunks,” Weiss explains. According to the researchers’ calculations, up to 3,000 cubic meters of water per second must have fallen into Jezero crater during these floods. Water agglomerates down the slope at a speed of up to nine meters per second.
According to Nangold and his team, this indicates that the climate of Mars changed dramatically around this time. The constantly humid temperate climate was followed by a phase in which it rained intermittently but heavily – similar to today in some desert regions of the world. “Our results indicate a temporal shift in the energy regime of western delta river systems – from continuous wet activity to powerful flood episodes that can sweep meter-sized rocks for kilometers,” the researchers wrote.
Thus, Jezero crater would have held valuable evidence of the change that transformed Mars from a wet, life-friendly world to a cold, dry desert planet. “Something very fundamental must have happened at this time in the planetary view,” Weiss says. However, the reason for this change is still unknown. (Science, 2021; doi: 10.1126/science.abl4051)
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