New research maps 965 potential chloride deposits on Mars, revealing clues about the planet鈥檚 ancient water-rich environments听
Researchers have created the first comprehensive map of potential chloride deposits on Mars, offering new insight into the planet鈥檚 ancient climate and geological history. Using the Colour and Stereo Surface Imaging System (CaSSIS) aboard the European Space Agency鈥檚 (ESA) Trace Gas Orbiter, researchers including Khalifa University鈥檚 Dr. Mohamed Ramy El-Maarry听deployed machine learning to analyze high-resolution, color-infrared images of Mars. They identified 965 candidate sites for chloride deposits, a class of minerals that form when water evaporates and leaves behind dissolved salts.听
Dr. El-Maarry, Associate Professor of Earth Science, collaborated with researchers from the University of Bern, Switzerland, and the University of Western Ontario, Canada. Their results were published in Nature鈥檚 .听
鈥淭he presence of chlorides on Mars is a fascinating subject because these deposits typically form in liquid water environments, such as lakes or shallow seas, where the water gradually evaporates, leaving salts behind,鈥� Dr. El-Maarry explained. 鈥淪uch deposits, common in Earth鈥檚 arid basins, are indicators that Mars once experienced significant episodes of liquid water on its surface. For planetary scientists, chloride-bearing terrains are a window into Mars鈥� distant past, around 3 to 4 billion years ago when Mars was likely warmer and wetter.鈥澨�
鈥淐hloride deposits serve as mineral markers of ancient water activity on Mars. They鈥檙e a high priority in the search for evidence of past habitability on the Red Planet.鈥�
鈥� Dr. Mohamed Ramy El-Maarry, Associate Professor, Earth and Planetary Sciences, Khalifa University
The research team developed a global dataset with chloride deposit candidates ranging from 300 meters to over 3 kilometers in diameter. Their work advances earlier research on Martian chlorides which was limited either by spatial resolution or image coverage. The team鈥檚 approach leveraged high-resolution CaSSIS data to locate previously undetected deposits and add detail to known sites.听听
One of the most innovative aspects of this approach is the application of machine learning to planetary geology. The team employed a neural network architecture trained to recognize the spectral characteristics and textures of chloride deposits. Chloride deposits on Mars typically appear light-toned and display a characteristic pink to violet hue in color-infrared images. By processing nearly 39,000 CaSSIS images, the neural network identified chloride candidates with a high average precision of 94.5% and near-perfect recall, reducing human biases common in manual image classification.听
鈥淭he distribution of chlorides in the dataset tells an intriguing story about Mars鈥� past,鈥� Dr. El-Maarry said. 鈥淢ost chloride candidates are in the southern highlands, with large deposits often found within ancient topographic depressions鈥攃raters and basins in low-albedo regions that suggest a once-wet environment. This aligns with previous studies showing a higher concentration of chlorides in the south, whether the planet鈥檚 climate likely supported rain and surface runoff about 3 billion years ago.鈥澨�
The team also made a breakthrough discovery: the identification of chloride-bearing terrain in the northern hemisphere of Mars. The northern chlorides are generally smaller and more degraded than those in the south, suggesting they may have experienced greater weathering and erosion, possibly from wind-driven processes or temperature changes over time.听
For scientists aiming to reconstruct Mars’ climate history, chloride-bearing deposits are key. Unlike other minerals, chlorides are soluble and can only survive where water has evaporated but remained largely isolated from later flowing water. The persistence of chlorides in the Martian crust implies stable water sources in the past, and their presence offers clues for where groundwater or surface water might have once been active.听
The implications for astrobiology are significant. In saline environments on Earth, microbial life has shown remarkable resilience, finding ways to survive and even thrive in extreme conditions. The discovery of chloride-rich terrains on Mars, particularly those sheltered from high radiation exposure, raises the possibility that ancient microbial life might have once existed in these regions.听
Jade Sterling听
Science Writer
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