The old Mars was hot with occasional rains, getting cold

Scientists have known for a long time that water was abundant in ancient Mars, but there was no consensus on whether liquid water was common or whether it was largely frozen in ice.

Was the temperature high enough to allow water to flow? Has this happened over a long period of time, or just occasionally? Was the surface desert or frozen? The warm conditions make it much more likely that life would have developed independently on the surface of ancient Mars. Now, a new comparison of the types of mineral deposits on the red planet with similar deposits on Earth suggests that the beginning of March had one or more long periods dominated by rainstorms and water flow, the water then becoming icy.

Presenting the results today at the Goldschmidt Conference on Geochemistry in Barcelona, ​​Professor Briony Horgan (Purdue University) said: "We know that there are times when the surface of Mars was frozen; we know that there were times when the water was flowing freely.know exactly when these times were and how long they lasted We have never sent unmanned missions in areas of Mars able to show us these oldest rocks, we must therefore use the science related to the Earth to understand the geochemistry of what could have happened there.

Our study of alteration under radically different climatic conditions, such as the Cascades in Oregon, Hawaii, Iceland and other regions of the Earth, can show us how the climate affects the structure of mineral deposits, such as we see it on Mars. Here on Earth, we find silica deposits in glaciers, characteristics of melting waters. On Mars, we can identify similar silica deposits in the youngest areas, but we can also see older areas that resemble the deep soils of hot Earth climates. This leads us to believe that 3 to 4 billion years ago, we had a slow general trend from hot to cold, with periods of thaw and freezing.

"So it is, it is important in the search for a possible life on Mars.We know that the building blocks of life on Earth grew very soon after the formation of the Earth, and that the presence of a living water is essential to the development of life.The increase of water on Mars will increase the chances that the simple life has developed at about the same time as on Earth. the Mars 2020 mission will be able to take a closer look at these minerals and begin to answer exactly what conditions existed when Mars was still young. "

The analysis of the geology of the surface of Mars confirms a trend of a warm climate to a cold climate, but the climate models themselves do not confirm it, because of the limited heat released by the young Sun. "If our conclusions are correct, we must continue to work on Mars' climate models, possibly including a chemical, geological or other process that could have warmed the young planet," Horgan said.

The research team compared Earth data with Martian minerals detected using the NASA CRISM spectrometer currently in orbit around Mars, which remotely identifies surface chemicals containing water. They also took data from the Mars Rover Curiosity. Professor Horgan is a co-investigator of the Mars 2020 mission, expected to be launched in July 2020 and begin exploring the Jezero crater in February 2021.

Scott McLennan, a professor at Stony Brook University, said: "What is particularly interesting in this work is that it has used well understood terrestrial geological processes from regions that are good analogues for Mars. The results are not only sensible from the point of view of developmental models of climate change for Mars, but also demonstrated a possible mechanism to form the most interesting and confusing and non-crystalline components that have been found in all the samples analyzed up to now by the Curiosity mobile. "(Professor McLennan was not directly involved in this work, it is an independent comment.)

The ancient valleys and lacustrine deposits on Mars clearly show that liquid water was once abundant on the surface, but it is not known if the climate was hot and humid or cold and cold. We suggest that the mineralogical archives of Mars could provide new constraints on the paleoclimate. Here we report a series of studies using analog soil samples from Mars on Earth to better understand the effects of climate on weathered mineralogy. Weather conditions in the alpine glacial areas of Oregon's Cascades are driven by frequent melting, and the residence time of water and sediments in the glacial system is low. Abnormal weathering properties on proglacial soils include silica coatings on bedrock and low crystalline silicates in glacial sediments. Preliminary results of mafic sediments on the cold margins of the Antarctic Ice Sheet also show weak crystalline silicates, consistent with degradation by a transient melting. On the other hand, hot zone sediments show enrichments in crystalline clay minerals, which we suppose to be formed due to the longer residence time under the ice cap.

Similar trends are observed in terrestrial mafic soils, from crystalline clay minerals in warm climate soils to low crystalline phases in cold climate soils. Silica signatures have been identified in orbit on Mars in Amazonian periglacial terrain, and the Curiosity robot has identified silica-poor crystalline materials in the Hesperian lacustrine sediments in the Gale Crater. We suggest that these amorphous phases on Mars could be formed in cold climates during punctured melting events. However, the most common noachian alteration signatures are crystalline clays in compound stratigraphies, for which the closest terrestrial analogues are deep weathering profiles known only to form under persistent dominated climates. by the rains. These observations suggest at least one climatic optimum of long life in the Noachian, but an in situ analysis of Noachian detrital sediments by March 2020 will be necessary to determine if the ice conditions prevailed in another way.

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Goldschmidt Conference