Analysis of large salt deposits on Mars suggests pools of liquid water have existed on the Red Planet for almost a billion more years than previously believed.
Hundreds of sodium chloride deposits spanning tens to hundreds of square kilometers were discovered by NASA's Mars Odyssey orbiter as early as 2008. These data had then proven that Mars was once much wetter, punctuated by lakes fed by rivers, providing a potential habitat for microbial life. As the planet's atmosphere thinned over time, this water eventually evaporated, leaving a desert world behind.
Until now, we thought the planet had dried up about three billion years ago . However, a study published in AGU Advances invites us to reconsider this delay.
For this study, as part of her doctoral work at Caltech, Ellen Leask and Caltech professor Bethany Ehlmann investigated salt chloride deposits left by the evaporation of icy meltwater flowing across the landscape. Specifically, they analyzed known salt deposits by examining what types of landforms they had formed on . This data was to help determine how they were deposited in the field in the first place.
To do this, the two researchers used data from the Mars Reconnaissance Orbiter (MRO) collected over the past fifteen years. At the end of their analyses, they then discovered that these deposits were surprisingly thin (less than three meters thick) and that they were in topographic depressions.
"The closest analogue we can find on Earth is the chains of lakes you get in Antarctica when the snow seasonally melts on top of the permafrost “, emphasizes Bethany Ehlmann. “Water cannot penetrate deep into the frozen ground below, so when it evaporates, the salt deposit left behind remains thin . »
Martian salt deposits are found here the most often in shallow depressions, sometimes perched above much larger craters devoid of deposits. According to the article, this orientation would seem to indicate that the water came from surface runoff during an ice freeze-thaw cycle, with chloride for the salt leaching from the top of the clay-rich soils.
During their analyses, the two researchers then discovered several chloride deposits at the top of a volcanic terrain formed 2.3 billion years ago . This discovery therefore raises new questions about the microbial lifespan that could have potentially survived on Mars.
