It’s drier than any desert on Earth. On Mars, pure water exists only as a gas or a solid. Vast amounts of ice are found at the north and south poles and buried underground, but there’s not a drop to drink.
“Liquid water isn’t stable on the Mars surface because of the temperatures and the pressures there,” says Sarah Milkovich, Mars research scientist at NASA’s Jet Propulsion Laboratory.
“Water on the surface will sublimate – if it is ice, it will go directly into the atmosphere in gas form.”
Yet strange features that look like flowing water appear in photos snapped by the HiRISE camera as it orbits the red planet. In Newton Crater, dark fingers stream downhill in warm seasons and fade in cold seasons.
A clue to the mystery was that rovers had discovered mineral salts in a soil sample. Experiments on Earth show that these salts can melt ice and let super-cold briny water flow free – even when conditions are cold enough to freeze pure water.
“If you’re mixing the salts and the water and you have the perfect conditions, then we think you should be able to have small flows of water very briefly on Mars,” says Sarah. “And we think we’ve seen them in HiRISE pictures.”
If you’re after more science activities for kids, subscribe to Double Helix magazine!