Even if there is water on Mars’s surface it may be too cold and salty for life as we know it to survive there – so there is no risk of contaminating Mars with Earth microbes Source: https://www.newscientist.com/article/2198191-water-on-mars-is-probably-too-cold-and-salty-for-life-as-we-know-it/?utm_campaign=RSS%7CNSNS&utm_source=NSNS&utm_medium=RSS&utm_content=home