When it heated a small pinch of dirt scooped up from the ground, the most abundant vapour detected was H2O.
Curiosity researcher Laurie Leshin and colleagues tell Science Magazine that Mars’ dusty red covering holds about 2% by weight of water.
This could be a useful resource for future astronauts, they say.
“If you think about a cubic foot of this dirt and you just heat it a little bit – a few hundred degrees – you’ll actually get off about two pints of water – like two water bottles you’d take to the gym,” Dr Leshin explained.
“And this dirt on Mars is interesting because it seems to be about the same everywhere you go. If you are a human explorer, this is really good news because you can quite easily extract water from almost anywhere.”
The dean of science at the Rensselaer Polytechnic Institute, New York, has been describing her work with Curiosity in this week’s Science In Action programme on the BBC.
The revelation about the amount of water chemically bound into the fine-grained particles of the soil is just one nugget of information to come from a series of five papers in the respected journal describing the early exploits of the rover.
Some of this data has been reported previously at science meetings and in Nasa press conferences, but the formal write-up gives an opportunity for the wider research community to examine the detail.