Scientists have discovered evidence that liquid water was once exposed to the air in ancient, shallow lakes on Mars. The finding is evidence that not all water on the Red Planet was covered in ice, as some Martian climate models suggest.
Planetary geologists and astronomers studying Mars have known for decades that water was once likely present on the planet, after NASA's Mariner 9 mission captured images of dry gullies in the 1970s. But there has been ongoing debate about what form that water took and how long it lasted. Some models predict that any liquid water on Mars' surface must have been covered by sheets of ice before it disappeared.
