New Mars images show ancient lakes
New satellite images suggest that Mars was warm enough to sustain lakes as recently as three billion years ago.
The research, by a team from Imperial College London and University College London, suggests that during the Hesperian Epoch, Mars had lakes made of melted ice, each around 20km wide, along parts of the equator.
The researchers say these lake beds might have formed habitats that could have been suitable for microbial life.
Earlier research had suggested that Mars had a warm and wet early history but that between four billion and 3.8 billion years ago, the planet lost most of its atmosphere and became cold and dry.
"Most of the research on Mars has focussed on its early history and the recent past. Scientists had largely overlooked the Hesperian Epoch as it was thought that Mars was then a frozen wasteland," says lead author Dr Nicholas Warner of Imperial. "Excitingly, our study now shows that this middle period in Mars' history was much more dynamic than we previously thought."
The researchers used images from the Mars Reconnaissance Orbiter to analyse several flat-floored depressions. Scientists previously believed that these might have been created by sublimation, where ice changes directly from its solid state into a gas. The loss of ice would have created cavities between the soil particles, causing the ground to collapse.
In the new study, the researchers analysed the depressions and discovered a series of small sinuous channels connecting them, which they reckon could only be formed by running water.
They say that increased volcanic activity, meteorite impacts or shifts in Mars' orbit could have warmed Mars' atmosphere enough to melt the ice.
The study appears in Geology.