Liquid Water on Mars

[Cross-posted to iScience]

NASA has announced the discovery of liquid water on Mars thanks to MGS images.

The clue is that the continual imaging by the MGS has enabled the team to track changes in the surface over time. The really exciting thing is that the team think that this shows evidence of material being moved by water today. The traces are light streaks in gulleys.

Photo by NASA

There are a few reasons why the scientists are arguing for the existence of water. One is the colour of these streaks. Usually when the dust gets disturbed on Mars, the surface gets darker. This is seen in the tracks the Mars rovers make, the trenches Viking made and the scars of impacts from space. These streaks are a lot lighter. Why the streaks are lighter is unknown, but there are couple of possibilities. The obvious explanation is that the light colour is due to frost. The favoured explanation is that this is the result of a mud flow. The surface is cold, so it’s possible that this is where water in a damp flow has frozen. The problem is could ice hang around long enough? David Michael Malin argues that the flows could taje a long while to dry out and so there’s continual precipitation into ice. However there is another weirder explanation.

The atmospheric pressure on Mars is very low. The lower the pressure, the lower the boiling point for a liquid. This is why you can’t get a good cup of tea high up in the Andes, the water boils at too low a temperature. On Mars water will boil even when it is cold, and this could be what is happening. The liquid water as it flows will be carrying minerals and possibly soluble salts. When the water boils it leaves the salt behind, so perhaps the streaks are these.

A serious problem is that it’s not just water that would flow on Mars. Dust can also tumble in avalanches. Could these be dust flows rather than water flows. Modelling at NASA suggests not. The flows are around a mile long down thirty degree slopes. The best match for the patterns is mud, as Martian soil* is carried by water. Additionally these flows are happening where dust flows are not found. They’re found in very different locations at different latitudes to these gullies.

The reason why they think this is current water is because these changes are visible in recent years. However, these aren’t Martian rivers. They’re closer to geysers. One of the scientists on the team said: “If you were there and this was coming down the slope you’d probably want to get out the way”. It would be rather like standing in front of a mud-slide. The volume of water would be about 10 to 15 swimming pools worth.

The new mystery is where is this water coming from? The most likely candidate is that this is ground water. Now is this frozen water that melts and escapes, or does the water exist in a liquid state beneath the Martian surface. David Michael Malin suggests that acidic water, rather than briny water could be liquid at lower temperature. On the other hand this could be melting ice or snow pack. If there is liquid water then it becomes possible that Mars may have life, even if only in the form of extremophiles – though from their point of view we’d be the extremophiles.

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