For the first time, satellite imagery reveals thick Martian salt deposits scattered across the planet's southern surface, which one planetary scientist claims could be sites of ancient life.
The mats of sodium chloride — the same taste-enhancing mineral found on your kitchen table — serve as more evidence of Mars' watery past, and researchers think the briney pools that made them could have been hospitable to life.
"If you're trying to find life on Mars, the more and different places that exist, the better the chances are that one of them is going to have the right conditions," said Phil Christensen, a planetary geologist at Arizona State University. "It takes a lot of water to form salt, so this is another place to look."
Christensen, who co-authored a March 21st study in the journal Science detailing the findings, said the salt deposits are a clear sign of water's past presence, adding that they could be the most welcoming environment for life on Mars yet discovered.
Take a chance
Christensen said the salt deposits probably formed from dried-up brine pools, which would not have been as acidic as other places on Mars where water is thought to have existed, such as clay and hydrated mineral deposits.
Sites such as those found by the Mars Exploration Rovers show sulfur in high levels, which means any water there may have been too harsh to support life.
"That's not the case with salt deposits, because they tend to not be acidic," Christensen said.
He added that some of the oldest organisms ever discovered on Earth have been found locked away in salt crystals, and that there may be Martian life forms entombed in the new crumbly flats that are about 3 to 10 feet (1 to 3 meters) thick.
"Salt is a fantastically good preserver, so maybe there's not only life but also organic compounds preserved there," Christensen told Space.com. "We need to send a rover to these places. I hope some day we will explore these salt sites on the ground."
Christensen said the route to identifying the salt deposits, thought to be more than 3.5 billion Earth years old, wasn't easy.
"Salt, it turns out, is pretty hard to detect," Christensen said, explaining that light analysis, or spectroscopy, of the mineral doesn't often show clear-cut signatures in satellite data. "They're actually very transparent, so there's generally a lot of difficulty in identifying them."
Using the Mars Odyssey orbiter's Thermal Emmission Imaging System, the research team found dozens of strange sites in a belt just south of Mars' equator. Christensen said it took them a couple of years to figure out what, exactly, they were.
"Once we realized we were looking at a transparent mineral, the light bulbs in our heads went off," he said. "When you look at the sites with visual satellite images, they look all the world like dried-up salt flats."
Christensen said a handful of planetary scientists are likely to be skeptical of his team's conclusion, but noted that a large majority should be on board.
"The spectroscopy of these salt sites is complicated, so I don't expect everyone will agree with us," he said. "Salts do this bizarre thing to spectrographs, so we have to do more singing and dancing to make the case."
In any event, Christensen said the sites he and his team have pinpointed are worthy of future investigation, especially if other ancient Martian water sites don't pan out to support life.
"I always worry that someone will say that's the end of the story for life on Mars if that happens," Christensen said. "I think these salt sites are really exciting. They may give us the best chance yet of finding something."
NASA funded the work by Christensen and his team.