Minerals that can only be formed in the presence of liquid water have again been detected on Mars, this time in huge craters in the low-lying terrain of the red planet's northern hemisphere.
The new survey found the so-called hydrated minerals in nine giant craters dotting the northern plains of Mars. The minerals appear to have been formed by liquid water more than 3 billion years ago, suggesting that past water on Mars altered the planet's surface much more significantly than researchers previously thought.
"The southern hemisphere of Mars is ancient ? over 4 billion years old," lead researcher John Carter, of the Centre National de Recherche Scientifique in Orsay, France, told SPACE.com. "It's highly cratered with lots of geological structures, and there are quite a few sites where we have these hydrated minerals. So, we already knew that there was likely liquid water on or near the surface of early Mars."
But, less was known about the mineralogy of the planet's northern hemisphere.
"There is a huge dichotomy between the northern and southern hemispheres of Mars," Carter said. "The northern hemisphere has very low-lying plains that are poorly cratered and very young ? less than 3 billion years old. They're very different in morphology and composition to the cratered southern highlands."
This latest discovery comes after the recent announcements that a vast ocean on Mars existed in the planet's ancient past and that liquid water from melting glaciers appears to have carved channels as recently as several hundred million years ago, more recently than previously thought.
Mars crater water clues
Carter and a group of French and American researchers analyzed data from NASA's Mars Reconnaissance Orbiter in order to probe the northern lowlands, which actually cover one-third of the planet.
The researchers examined large Martian craters, on average ranging from about 10 miles (16 km) to 37 miles (60 km) in diameter. They also investigated one crater, the largest in the northern plains, that was130 miles (210 km) wide.
The region was thought to have been resurfaced by lava flow approximately 3 billion years ago, and scientists were unsure whether hydrated minerals had been preserved in the crust. Additionally, deposits of dust and ice ? part of the process called mantling in which Martian lava, dust and ice reshape the planet's surface ? have altered the terrain in the northern lowlands.
So, while most of the large-sized craters share similar structure and features, the mantling process prevented some sites from delivering usable data. As a result of such mantling, Carter and his colleagues had to contend with a smaller sample size.
The researchers detected water-bearing minerals in nine craters. These minerals were likely buried by intense lava flow, and eventually excavated by subsequent meteor impacts that transformed the resurfaced northern region of the planet.
"Although we don't have as many sites in the north, we do see most of the variety of the minerals found in the south," Carter said. "This is an indication that Mars had liquid water on the surface, or near the surface, not only in the south, but in the north as well. It was not just localized in areas in the south, it was everywhere."
Water reshaped surface of Mars
But, Carter is quick to clarify that these findings do not imply that Mars once had flowing oceans on its surface. In fact, while it does provide further confirmation of Mars' wet era, the study indicates that the planet did not actually have an intense system of water flow.
"Very early Mars ? and we're talking 4 to 4.3 billion years ago ? was indeed very much altered by liquid water both in the southern and northern hemisphere," Carter said. "But, most of the minerals we're seeing are formed on Earth in very dry environments, so this doesn't really change our view of Mars' early environment. The mineral assemblages that we're seeing point to a weak hydrological system. So, there were probably small bodies of water like rivers, deltas and crater lakes, but we're not expecting huge oceans."
Still, the study's findings, which are detailed in the June 25 issue of the journal Science, will help researchers understand more about the evolution of our neighboring planet. And, said Carter, the study has important implications for the ongoing search for life on the red planet.
"This shows us that the water stability era that was possibly conducive to the formation of life was widespread, so it's good news for the search for life," Carter explained. "But, those sites that we're seeing are not as extensive or altered as a few sites that we're seeing in the south that have been studied for years. Several rovers that will be sent to Mars in the years to come will have a list of important sites on Mars that have the best potential for finding fossil life."