NASA finds evidence that liquid water exists on Mars today

DW: So have we found liquid water on Mars?

Ralf Jaumann: Well, yes, the discovery is that of liquid water but it is extremely rich in salt, and that's one of the reasons we can see it on the surface on Mars. First, salt reduces the melting point of ice, so it's possible to have liquid water below zero. And we need salt for this to happen, because it's very cold on Mars. Second, the density of salt-rich water is higher than the density of pure water, so salt water can remain for longer on the surface with the low [atmospheric] pressure found on Mars.

Is that an important discovery?

Yes, but it's very small-scale - it's only on a crater wall which has shown some mud slumping and mass wasting, including this salt water. It's only in the order of a few hundred meters, or tens of meters in width.

But - and this is the most important thing besides the discovery of water - it changes with the seasons. This means in summer the ice melts and it runs down the crater wall, and in winter it's still freezing and the mass wasting and the mud slumping happens less than in summer, so there's a cycle. It happens every martial year.

But if the water is really flowing, it means this is more than just traces - there must be larger amounts of it, or not?

It's traces, and as I say, it's very small scale. The amount of water is not very much at all - I can't be sure, but I doubt we're talking about more than [the equivalent of] a few bathtubs full of water - every year. We're not seeing a big lake. It's just a water saturated mud stream flowing down a hill.

Even so, the discovery of water on Mars is spectacular, isn't it?

It is, because now we know what to look so that we can go back and sample these areas. Once you have liquid water, there's a chance of finding astrobiological organic material. So if the astrobiologists want a sample from Mars, they would go to these areas, where they know they can find salt-rich mass wasting, slumping material.

So there could be a chance of finding life on Mars?

Yes, but I don't think we'll find life with the instruments we have on Mars, or even the rovers we have there. So we need a sample. And with this discovery, we now know where we have to look to get those samples on Mars, and bring them back to Earth.

But could life "as we know it" exist in this salty water on Mars?

I think so, because life as we know it - small-scale life like bacteria - can exist in salty water on Earth. They could also exist in sulfur-rich areas on Mars, they exist in very hot and very cold environments, and so it's probably very feasible that such small life exists on Mars, too. But to prove this we would need a sample from this area where this liquid water was found on the surface.

Is this really the first time scientists have found liquid water on Mars?

We have a lot of traces suggesting liquid water existed in the past - but this is the first indication of liquid water existing today. This is the first time we've seen H2O liquid on the surface.

What did you think personally when you first heard about this discovery?

Well, it was what I had expected, because of the physical models we have of Mars and the fact we know there is ice in the sub-surface, and we know there are weathered rocks, and weathered rocks usually consist of salts and clay minerals, and if you bring ice, salt and clay minerals together, they react - so we have expected that there is this kind of salt-rich water in the sub-surface or salt-rich ice in the sub-surface. But to have a model is one thing - that's theory. But to really discover it is another thing, because that tells you your theory is correct, and that nature is doing what you want it to do!

Was it a difficult discovery to make?

Well, I say it's not really that the water which is salt-saturated, but that the salt is water-saturated - and these kinds of measurements are very difficult, and the only way to do this from the Martian orbit was with an instrument on a NASA Mars orbiter, and it's very tricky to resolve this small-scale chemical compound. It's small-scale in the area it covers and it's small-scale in its spectral extension, but it's a very big scientific effort to find such spectral signatures on a surface. So I think it's a big deal.

Prof. Dr. Ralf Jaumann heads the Institute of Planetary Research at the German Aerospace Center in Berlin.