(CN) – While exploring a giant crater on Mars, NASA’s Curiosity rover detected salt-bearing sediments within ancient crater rocks, which suggests a lake was once present there before the planet transitioned to arid climates over billions of years, according to a study released Monday.
The 1-ton, nuclear-powered Curiosity rover is exploring the red planet’s Gale Crater in order to help scientists understand how water disappeared from Mars’ surface.
Geological studies of the red planet’s surface by American and European satellites show that a network of both underground and surface-level lakes once dotted the Martian landscape, including a vast ocean occupying nearly half of the planet’s northern hemisphere.
Sulfate, carbonate and chloride salts detected by probes orbiting Mars help scientists understand the past chemistry of ancient lakes.
In a study published in Nature Geoscience, scientists said the Gale Crater sediments discovered by Curiosity display “geochemical fingerprints” of ancient lakes that transformed into brines as the red planet became more arid around 3.5 billion years ago.
Researchers have not detected this level of sulfate salts in older sediments previously discovered by Curiosity, according to William Rapin with the California Institute of Technology in Pasadena, California and other colleagues.
“We know from orbital observations during that timing Mars was changing radically, over geological times, although it still had liquid water, lakes, rivers, and also important volcanic activity it was losing its atmosphere to space,” Rapin said. “We know for sure this deeply affected its climate. Using Curiosity data, we can study for the first time hundreds of meters of stratigraphy, recording some of what occurred in Gale crater at that crucial time of Mars history.”
As Mars became more arid during its Hesperian period, the planet’s lake basins reached higher salinity as water evaporated from the surface, according to Rapin.
“In this study we highlight that the lake that once existed in the crater, later became saline enough to crystallize salts due to fluctuations of the climate,” Rapin said.
Scientists believe much of Mars’ water is trapped underground or in its polar ice caps though NASA’s Maven spacecraft is studying how charged solar particles may have played a role in drying out the red planet over time.
Curiosity, which has previously discovered an ancient stream bed on the red planet, will analyze younger rocks in Gale Crater as researchers continue their search for clues on how Mars dried out over time.
“We’re discovering a reality of climatic fluctuations, between wetter and drier periods, that informs us on the types of ions that were available in water running on the surface at the time, and what type of environmental change life had to cope with if it ever existed then,” Rapin said.
Along with capturing stunning images of the Martian landscape, Curiosity is also searching for complex microbes and evidence that life-sustaining conditions once existed. It hasn’t found any yet.