Chloride deposits are a sign of Mars’ early, water-rich past and have important implications for understanding Mars’ climate and habitability. Using high-resolution colour infrared images taken by the Colour and Stereo Surface Imaging System (CaSSIS) on board ESA’s Trace Gas Orbiter (TGO), planetary scientists have conducted a planet-wide search for chloride-containing deposits in Terra Sirenum and other regions of Mars.
This CaSSIS/TGO image shows chloride-containing deposits (purple scaly wave) in Terra Sirenum, Mars. Image credit: ESA / TGO / CaSSIS.
“Mars is today a desert world that was covered by rivers, lakes and possibly oceans about 3.5 billion years ago,” say researcher Valentin Bickel from the University of Bern and his colleagues.
“A cold era began when Mars lost its magnetic field and could no longer hold its own atmosphere, causing water to evaporate, freeze, or become trapped in the surface.”
“As the water disappeared over time, it left mineral fingerprints on the surface.”
In the study, researchers used a neural network to map potentially chloride-containing deposits in CaSSIS images across a significant portion of Mars.
They identified a total of 965 candidates for chloride deposits with diameters between 300 and 3,000 m.
“Most likely, these salt deposits were formed from shallow water or saltwater pools that evaporated in the sun,” the scientists said.
“Using a similar method, humans produce salt for human consumption in saltwater basins on Earth.”
“Very salty waters could have become a paradise for life, a beacon for habitable places on Mars,” they added.
“High salt concentrations ensure that water remains liquid even at temperatures as low as minus 40 degrees Celsius.”
“The chloride deposits in the image above and their direct relationship to liquid water make areas like Terra Sirenum good targets for future robotic missions looking for signs of life.”
“Chloride-containing terrain is not noticeable in normal black-and-white images, but shows up as a distinct purple hue in color infrared images, making CaSSIS a unique tool for studying salt distribution on Mars.”
“Our work provides unprecedented data that help us better understand the distribution of water in Mars’ distant past,” they said.
“TGO continues to take images of Mars from orbit to understand its distant past and potential habitability.”
“The spacecraft will not only provide spectacular images, but will also provide the best inventory of atmospheric gases and map the planet’s surface in search of water-rich areas.”
“Understanding the history of water on Mars and whether it once supported life is at the heart of ESA’s ExoMars missions.”
The team’s article appeared this month in the magazine Scientific data.
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VT Bickel et al. 2024. A global dataset of potential chloride deposits on Mars identified by TGO CaSSIS. Scientific data 11, 845; doi: 10.1038/s41597-024-03685-3
