Mars had liquid water on its surface recently, according to new images.
The water may have started as snow that melted.
Chinese researchers found cracked layers on Martian dunes.
The finding suggests Mars was once a salt-rich watery world.
The study used data from China's Zhurong rover.
The rover explored Mars' northern hemisphere since May 2021.
The dunes had thin, fractured crusts that formed from melting water.
The melting occurred between 1.4 million and 400,000 years ago.
Early Mars had abundant liquid water 3 billion years ago.
Climate changes froze much of it as ice now locked in poles.
Water vapour travelled from Martian poles to lower latitudes.
The planet's polar ice-caps released high amounts of water vapour.
Mars' poles were pointed more directly towards the sun.
Frigid temperatures condensed the drifting vapour and dropped it as snow.
The study was published in the journal ScienceAdvances.
The findings challenge previous assumptions about Mars' water history.
Further studies may shed light on the planet's potential for habitability.