Mars had drier and wetter eras before drying up completely in the Hesperian period, about 3 billion years ago, according to an analysis of observational data collected by NASA’s Curiosity in the Martian Gale Crater.
Mars had drier and wetter periods and dried up for good 3 billion years ago. Image credit: M. Kornmesser / ESO / N. Risinger, skysurvey.org.
“A primary goal of the Curiosity mission was to study the transition between the habitable environment of the past, to the dry and cold climate that Mars has now,” said Dr. Roger Wiens, a researcher at Los Alamos National Laboratory.
“These rock layers recorded that change in great detail.”
Dr. Wiens and colleagues used the Remote Micro-Imager of the ChemCam instrument on the Curiosity rover to make detailed observations of the steep terrain of Mount Sharp in Gale Crater.
They found that the Martian climate alternated between dry and wetter periods before it went completely dry.
Moving up through the terrain, Curiosity observed that the types of the sedimentary beds change drastically.
Lying above the lake-deposited clays that form the base of Mount Sharp, sandstone layers show structures indicating their formation from wind-formed dunes, suggesting long, dry climate episodes.
Higher up still, thin alternating brittle and resistant beds are typical of river floodplain deposits, marking the return of wetter conditions.
These changes in terrain show that the climate of Mars underwent several large-scale fluctuations between wetter and dryer periods, until the generally arid conditions observed today took hold.
View of the slopes of Mount Sharp in Gale Crater on Mars, showing the various types of terrain that have been and will be explored by the Curiosity rover. The sedimentary structures observed by ChemCam’s telescopic images (mosaics A and B) reveal clues about the ancient environments in which they formed. Image credit: NASA / JPL-Caltech / MSSS / CNES / CNRS / LANL / IRAP / IAS / LPGN.
“Our results indicate a transition from lacustrine mudstones into thick aeolian deposits, topped by a major deflation surface, above which strata show architectures likely diagnostic of a subaqueous environment,” the researchers said.
“Our model offers a reference example of a depositional sequence for layered sulfate-bearing strata, which have been identified from orbit in other locations globally.”
“It differs from the idea of a monotonic Hesperian climate change into long-term aridity on Mars and instead implies a period characterized by multiple transitions between sustained drier and wetter climates.”
The findings are published in the journal Geology.
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W. Rapin et al. Alternating wet and dry depositional environments recorded in the stratigraphy of Mount Sharp at Gale crater, Mars. Geology, published online April 8, 2021; doi: 10.1130/G48519.1
