We tend to think that Mars is as dry as a Noel Coward comedy, but it wasn't always like that. At a press conference on Monday, NASA revealed that data from its Curiosity Mars rover indicates that the Gale Crater area that the robotic explorer has been traversing for over two years may once have been a circular lake that filled and refilled over a period of tens of millions of years.
According to NASA, the new data shows how the forces of ancient Mars carved out the lower slopes of the 2-mi (5-km) high Mount Sharp from the sediments that were deposited on the bed of Gale Crater in the Red Planet's ancient past. If this is the case, it indicates that the Martian environment was once more Earthlike with an atmosphere dense and warm enough to not only allow liquid water to be present on the surface, but also to flow and collect repeatedly enough times as a series of lakes to leave behind hundreds of alternating layers of sediments and wind deposits.
NASA scientists say that the key to unlocking this mystery is a 500-ft (150-m) section of rock called the Murray Formation, which Curiosity has been studying as it rolls 5 mi (8 km) from its 2012 touchdown site at Bradbury Landing. These repeated layers of silt and sand were carried into the crater by rivers fed by melting snow at the crater rim until they created river deltas on the bottom. This accumulation eventually reached a depth of hundreds of meters, after which wind erosion carved out the modern slopes of Mount Sharp – uncovering the sediments for Curiosity's exploration.
"The great thing about a lake that occurs repeatedly, over and over, is that each time it comes back it is another experiment to tell you how the environment works," says Curiosity Project Scientist John Grotzinger of the California Institute of Technology in Pasadena, California. "As Curiosity climbs higher on Mount Sharp, we will have a series of experiments to show patterns in how the atmosphere and the water and the sediments interact. We may see how the chemistry changed in the lakes over time. This is a hypothesis supported by what we have observed so far, providing a framework for testing in the coming year."