Crusty, dusty and rusty describes the Mars of today.
Surface features of the Red Planet, however, hint at a watery past where torrents of groundwater carved out deep canyons, formed sweeping fans of sediment and cemented together huge fault lines.
"Groundwater probably played a major role in shaping many of the things we see on the Martian surface," said George Postma, a sedimentologist at UtrechtUniversity in the Netherlands.
Postma collaborated with Virginia Tech's Erin Kraal and others to recreate Mars' fan-like sediment deposits with a scale model. The group detailed their findings in a recent issue of the journal Nature.
A separate new study by Allan Treiman, a scientist at the Lunar and Planetary Institute in Houston, details the role of groundwater in depositing minerals in rocky Martian crevices.
Scientists think a massive ocean once covered one-third of Mars, and recent photographs suggest that pockets of water may still be hidden beneath the planet's surface. Water is crucial for life as we know it, so signs of underground water now — and more extensive amounts of water in the past — both suggest Mars was or might still be habitable, at least to microorganisms.
Postma said such reservoirs of water probably carved out canyons, rapidly depositing step-like layers of sediment in Martian impact craters across the planet.
"When we examined photographs of Mars, we saw that some deltas had steps of material," Postma told SPACE.com. He noted that such formations are seen on Earth only where water rapidly deposits delta sediment, such as parts of the Sahara Desert's Lake Chad.
"Based on our models, these structures might have been caused by catastrophic events that filled the craters in one go," he said. Instead of taking millions of years to form, Postma said the fans probably formed in decades.
Ancient torrents of water spilling out of Martian ground with the output of the Mississippi River, for example, could have formed some of the dozen step-like sediment fans the researchers observed in about 13 years.
"Another puzzling feature is that you don't see a drainage network along the crater's side," Postma said — yet another clue that fans' formations were rapid and not the product of rainy runoff. "Craters are thought to be very porous, so the water can sink through. Another possibility is that the water just evaporated into the Martian atmosphere."
In Valles Marineris, where about 2,500 miles (4,000 kilometers) of 6-mile-deep (10-kilometers) chasms dwarfing the Grand Canyon stretch over Mars, Treiman thinks he has located more evidence of groundwater at work.
"Groundwater is a crucial reservoir in Mars's global water cycle and plays an important role in the alteration of bedrock," Treiman writes in his study, detailed yesterday in the journal Nature Geoscience.
The Valles Marineris canyons formed when massive slabs of rock both lifted up and sunk, creating fault lines in the process. Spacecraft imagery of the landscape shows the crevices as ridges, which Treiman thinks were filled with mineral-rich groundwater between 3.5 billion and 1.8 billion years ago.
"This interpretation implies that liquid water was stable at or near Mars's surface when the fault zones were cemented," Treiman said, noting that only a "warm wet" climate on Mars could have made the deposits possible.
"The presence of liquid water is important in current ideas of Mars's history," Treiman said, "and central to Mars's potential for life."