ientists think they can now tie dark streaks seen on the surface of Mars to periodic flows of liquid water.

Data from a Nasa satellite shows the features, which appear on slopes, to be associated with salt deposits.

Crucially, such salts could alter the freezing and vaporisation points of water in Mars's sparse air, keeping it in a fluid state long enough to move.

Lujendra Ojha and colleagues report the findings in the journal Nature Geoscience.

There are implications for the existence of life on the planet today, because any liquid water raises the possibility that microbes could also be present. And for future astronauts on Mars, the identification of water supplies near the surface would make it easier for them to "live off the land".

Researchers have long wondered whether liquid water might occasionally flow across the surface today.

 

It is not a simple proposition, because the temperatures are usually well below zero Celsius and the atmospheric pressure is so low that any liquid H20 will rapidly boil.

 

uite where the water is coming from to make the streaks is still unclear, however. The locations studied by MRO are equatorial, and any stored water in this region of Mars, perhaps in the form of ice, is thought to exist only at great depth.

One possibility is that the salts actually pull the water out of the atmosphere. But again, it is not known whether there is a sufficient supply in the air to facilitate this.

Another theory is that local aquifers are breaking up to the surface, but this does not really fit with streaks that appear from the tops of peaks.

It is conceivable that streaks are being formed from different sources in different parts of Mars.

Contamination question

Dr Joe Michalski is a Mars researcher at the Natural History Museum in London. He called the announcement an exciting development, especially because of its implications for the potential of microbes existing on the planet today.