Mars\u2019 ancient climate is one of our Solar System\u2019s most perplexing mysteries. The planet was once wet and warm; now it\u2019s dry and cold. Whatever befell the planet, it didn\u2019t happen all at once.<\/p>\n
New research shows that on ancient cold Mars, sheets of frozen carbon dioxide allowed rivers to flow and a sea the size of the Mediterranean to exist. <\/p>\n
<\/p>\n Mars\u2019 climatic change from warm and wet to cold and dry wasn\u2019t abrupt. There was no catastrophic impact or other triggering event. Throughout its gradual shift, there were different climatic episodes.<\/p>\n The planet\u2019s surface is characterized by features that indicate water\u2019s presence. River channels, impact craters, and basins that were once paleolakes illustrate Mars\u2019 complex climatic history. Mars is much different from Earth, but they both follow the same set of natural rules. <\/p>\n In Earth\u2019s frigid climates, rivers can flow underneath thick, protective ice sheets. New research shows that a similar thing happened on Mars. The research is published in JGR Planets and is titled \u201cMassive Ice Sheet Basal Melting Triggered by Atmospheric Collapse on Mars, Leading to Formation of an Overtopped, Ice-Covered Argyre Basin Paleolake Fed by 1,000-km Rivers.\u201d The lead author is Peter Buhler, a Research Scientist at the Planetary Science Institute. <\/p>\n The research examines a period about 3.6 billion years ago when Mars was likely transitioning from the Noachian Period to the Hesperian Period. At that time, most of the surface water was frozen into large ice sheets in Mars\u2019 southern region, according to the research. The planet\u2019s CO2<\/sub> atmosphere suffered periodic collapses, and sublimated out of the atmosphere. Those collapses formed a layer of CO2<\/sub> 650 meters (0.4 miles) thick that created a massive ice cap over the South Pole. It insulated the 2.5-mile-thick (4 km) layer of frozen water that made up the ice sheets.<\/p>\n Buhler modelled how the CO2<\/sub> cap acted as a thermal blanket and showed that it released massive amounts of meltwater from the frozen pole. This water flowed down rivers, with the top layers freezing and insulating the liquid water underneath. <\/p>\n \u201cYou now have the cap on top, a saturated water table underneath and permafrost on the sides,\u201d Buhler said. \u201cThe only way left for the water to go is through the interface between the ice sheet and the rock underneath it. That\u2019s why on Earth you see rivers come out from underneath glaciers instead of just draining into the ground.\u201d<\/p>\n According to Buhler\u2019s work, enough water was liberated to fill the Argyre Basin. <\/p>\n The Argyre Basin is one of the largest impact basins on the planet, measuring roughly 1800 km (1100 mi) in diameter. This massive impact basin was formed billions of years ago by a comet or asteroid striking Mars. It drops about 5.2 km (3.2 mi) below the surrounding plains, making it the second deepest basin on Mars. Scientists have long thought that the basin once held water\u2014as much as the Mediterranean Sea\u2014and Buhler\u2019s work shows how it may have filled. <\/p>\n \u201cEskers are evidence that at some point there was subglacial melt on Mars, and that\u2019s a big mystery,\u201d Buhler said. Eskers are long stratified ridges of sand and gravel deposited by meltwater streams that flow under glaciers. They\u2019re common on Earth, where glaciers once covered the surface. Mars\u2019 eskers support the idea that the same thing happened on that planet. <\/p>\n The subglacial rivers would have flowed underneath the ice, where they were insulated from the cold. When they exited the glacier, they would have oozed along until a thick enough ice cap formed to insulate them. Buhler says that the ice would\u2019ve grown until it was hundreds of meters thick, and the water flowing under the ice caps would\u2019ve been several feet deep. The water would\u2019ve carved out river channels thousands of miles long, and there are several of those that go from the polar cap to the Argyre Basin. <\/p>\n \u201cPeople have been trying to discover processes that could make that happen, but nothing really worked,\u201d Buhler said. \u201cThe current best hypothesis is that there was some unspecified global warming event, but that was an unsatisfying answer to me, because we don\u2019t know what would have caused that warming. This model explains eskers without invoking climatic warming.\u201d <\/p>\n Argyre Basin is massive and voluminous, and proposed explanations for how it was filled with water were left wanting. It has approximately the same volume as the Mediterranean Sea. Buhler\u2019s model shows that it took about ten thousand years for the basin to fill, and after it filled, the water emptied into plains about 8,000 km (5,000 miles) away. <\/p>\n This process happened repeatedly over a one-hundred-million-year era, with each event separated by millions of years. <\/p>\n \u201cThis is the first model that produces enough water to overtop Argyre, consistent with decades-old geologic observations,\u201d Buhler said. \u201cIt\u2019s also likely that the meltwater, once downstream, sublimated back into the atmosphere before being returned to the south polar cap, perpetuating a pole-to-equator hydrologic cycle that may have played an important role in Mars\u2019 enigmatic pulse of late-stage hydrologic activity. What\u2019s more, it does not require late-stage warming to explain it.\u201d<\/p>\n Buhler\u2019s work is supported by other research. \u201cPrevious literature supports the presence of a ~0.6 bar (atmospheric) CO2<\/sub> inventory, as utilized in the model, near the Noachian-Hesperian boundary,\u201d he writes in his research. The history of Mars\u2019 atmospheric pressure is backed up by cosmochemistry, mineralogy, atmosphere and meteorite trapped-gas isotopic ratios, geomorphology, and extrapolations of modern-day atmospheric escape. <\/p>\n \u201cThus, there is strong evidence that Mars had a sufficiently large mobile CO2<\/sub> reservoir to drive the atmospheric-collapse-driven melting scenario described in this manuscript, with collapse occurring at a time commensurate with Valley Network formation during Mars\u2019 intense, Late Noachian\/Early Hesperian terminal pulse of intense fluvial activity,\u201d Buhler writes. <\/p>\n That period of Mars\u2019 history stands out as its own distinct phase of geological activity, whereas changes were more gradual in the earlier Noachian Period. The Late Noachian\/Early Hesperian saw intense valley network formation. Many of these valleys are deeply carved into the landscape, often cutting through older geological features. That suggests that the water flow was powerful and erosive. This fluvial activity also created large deposits of sediment, like the ones NASA\u2019s Perseverance Rover is exploring in Jezero Crater.<\/p>\n Buhler\u2019s research is partly based on modern-day observations of Mars\u2019 atmospheric CO2<\/sub> and its cycles. Much of it is actually frozen and bound to the regolith. Mars\u2019 rotational tilt shifts over a 100,000-year timeline. When it\u2019s closer to straight up and down, the Sun hits the equator, and CO2<\/sub> is released from the regolith into the atmosphere. It eventually reaches the poles, where it\u2019s frozen into the caps. <\/p>\n When Mars is tilted, the poles are warmed, and the CO2<\/sub> sublimates and is released into the atmosphere again. It eventually reaches the now-cooler regolith, which absorbs it. \u201cThe atmosphere is mostly just along for the ride,\u201d Buhler said. \u201cIt acts as a conduit for the real action, which is the exchange between the regolith and the southern polar ice cap, even today.\u201d<\/p>\n Buhler is still working with his model and intends to continue testing it more rigorously. If it successfully withstands more testing, our understanding of Mars will take a big leap forward. <\/p>\n![\"These](\"https:\/\/www.universetoday.com\/wp-content\/uploads\/2024\/11\/1440px-Fulufjalletesker-1024x768.jpg\")
![\"\"](\"https:\/\/www.universetoday.com\/wp-content\/uploads\/2024\/11\/Argyre-Crater-Meltwater.jpg\")
![\"Jezero](\"https:\/\/www.universetoday.com\/wp-content\/uploads\/2024\/01\/Jezero-Crater-1024x683.jpeg\")
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