Experts suggest much of the water Mars once had is now locked up in minerals.
Three thousand days and counting: Nasa's Curiosity rover continues its extraordinary exploration of Mars.
The US space agency releases an animation to show how its Perseverance robot will land on Mars.
The oxygen in Martian air is changing in a way that can't currently be explained by known chemical processes.
Nasa's Mars robot records its largest measurement yet of methane in the Red Planet's air.
A European spacecraft has confirmed a report of methane being released from the surface of Mars.