A long-lasting lake on ancient Mars may have shown chemical differences between deep and shallow water — a common feature of layered lakes on Earth whose diverse conditions offer varied environments for microbes to thrive, according to a new study by an international research team including a University of Guelph physicist.

The paper published today in Science draws on data collected over the past three years by NASA’s Curiosity Mars rover, including information from a rover instrument built in Canada and now being monitored by a group led by physics professor Ralf Gellert.

He said recent samples collected by the robotic device suggest that a sizable portion of the floor of the red planet’s Gale Crater is covered by fine-grained, homogeneous mudstone whose composition changes in characteristic ways with elevation.

“The only thing that could do that is water,” said Gellert. Referring to earlier findings by Curiosity and other rovers, he added: “This is evidence yet again of water on Mars 3 ½ billion years ago.”

Since landing in 2012, the rover has travelled to the foothills of a layered mountain inside the crater. Climbing uphill, Curiosity is now within reach of progressively younger rock layers where earlier analyses by a Mars orbiter showed evidence of minerals likely deposited by ancient water.

Gellert said the rover’s planned route further up the side of Mount Sharp will enable scientists to test those younger rock layers and, in effect, track environmental changes that occurred over billions of years.

Last month, the Canadian Space Agency extended funding worth a total of $1.5 million over two years for Canadian researchers to continue operating the U of G-led instrument and analyzing its findings.