What's so important about flowing water on Mars? By Dr. Lewis Dartnell, astrobiology research fellow at the University of Leicester and author of 'Life in the Universe: A Beginner's Guide'------This blog is part of our series of space blogs for World Space Week; Explore the evolution of spacesuits, listen to an audio tour of the active missions in the solar system, or hear the soundtrack for space exploration on our blog. This week is World Space Week and, for me, the most exciting announcement of the year has been the discovery of signs of liquid water flowing on the cold, dusty surface of the planet Mars. Luju Ojha and his team used one of our probes orbiting Mars to study curious dark lines that have been spotted streaking downhill in many different locations, but always during summer as the ground warms up. One hypothesis had been that these were caused by water thawing out of the permafrost and running downstream, but we didn't have any evidence to back this up. And this is exactly what Ojha has now found (using 'infrared spectroscopy' from orbit): areas of damp salts along the streaks, which would have been deposited as briny water flowed and then dried up again. The dissolved salts are able to keep the water from freezing even at the punishingly low temperature of -20°C -- it's the same reason we spread salt on icy roads in winter. The fact that Mars still flows (well, ok, trickles....) with liquid water today is a huge discovery - it tells us that our next door neighbour is still a geologically active and dynamic world. We can see hard-frozen water ice at the north and south poles of Mars (the red planet has white polar ice caps, just like Earth) and there are lots of ancient channels, river valleys and dry lake beds that tell us Mars was once much warmer and wetter than it is today. But up until now we had no convincing evidence that liquid water flowed still today on the face of Mars. What's also great about the story is that this big discovery follows on from work that Luju Ojha did while he was still an undergraduate student. I think it's amazing to think what you can accomplish only just out of school! Many scientists, including myself, are also very excited because liquid water is the vital fluid for biology, and Mars is thought to hold one of the best hopes for life beyond the Earth. We know of certain microorganisms on Earth, known as extremophiles, that can tolerate very hostile conditions, including high salt concentrations. The problem with the salty seeps we've just discovered on Mars, though, is that they could be too salty for life as we know it to survive. The scientists didn't see the tell-tale signature of sodium chloride -- sea salt that we're familiar with on Earth -- but magnesium chlorate and sodium perchlorate. (Remember that, in chemistry terms, a salt is simply a compound of an anion, an atom that’s gained an electron, and a cation, an atom that’s lost an electron, so 'salt' actually encompasses a large category of different substances). These kinds of salts are very challenging for life to survive in, so the hope is that there is also more habitable water in environments on Mars. This discovery of water on Mars underscores another possibility for life on Mars though: us. The first human missions to Mars will need to make as much use of resources they can gather on Mars itself, rather than the huge expense of launching everything from Earth. So areas of underground water that could be dug up and purified for drinking will be crucial. And using electrolysis you can split water into oxygen for breathing, and hydrogen that is used as rocket fuel. Mars colonists would also need to grow all their own food: to become space farmers. Scientists are trying to work out which crops would be best suited for growing in inflatable greenhouses, and how to turn dusty martian regolith into fertile soil. Mars rock has all of the essential elements needed by plants, once moisture and some nitrogen-rich fertiliser has been added. (Matt Damon's character in the new blockbuster film 'The Martian' has a revolting solution for this, but I won't ruin the surprise for you...). The BSA has a suggestion for a CREST Bronze Award science project investigating the properties of soil needed to support plant growth. Who knows, maybe in a few years you might be tucking into Mars-grown salad (rocket salad, of course!) whilst gazing out the airlock window at the rusty martian landscape. Lewis is also running a nationwide schools outreach project, with the Astrobiology Society of Britain. The ASB has been funded by the UK Space Agency to deliver a number of free events to KS2 and KS4 pupils at schools across the country, linking to UK astronaut Tim Peake's mission to the International Space Station. The STARS project hopes to inspire pupils at KS2 & 4 to engage with STEM subjects, and to provide role-models through face-to-face interaction with practising space scientists and astrobiologists. Discover how your school can apply for the programme. Celebrate World Space Week- Take part in a space-themed CREST project or discover more about deep space with our space blog series. Image credit: NASA/JPL-Caltech/Univ. of ArizonaDark narrow streaks, called "recurring slope lineae," emanate from the walls of Garni Crater on Mars, in this view constructed from observations by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter.