In 2011, NASA’s Mars Reconnaissance Orbiter (MRO) provided images that showed dark streaks in the soil in areas near the equator. They faded over time but they return at the warmest part of each year. The atmosphere is much too thin to retain liquid water for long periods of time but these images are evidence that certain areas of Mars may have free flowing water during certain times of the year. The results come from Alfred McEwen of the University of Arizona and were published in Nature Geosciences.
Image: Nature Geoscience / Alfred McEwen et al.
Researchers don’t know enough about Martian geology so they can’t be sure of where the water could be coming from. There could be pockets of ice underneath the surface that liquefy when warmed, but the emergence pattern of the dark streaks doesn’t seem to suggest that. There is also a possibility that the streaks are caused by water vapor being pulled from the atmosphere and condensed into the soil.
If there were any traces of Earth microbes on the probes that will visit these potentially watery areas, these areas could easily be contaminated. So the probes must be completely sterilized using hydrogen peroxide vapor heating or ionized radiation, a complicated and expensive procedure but having accurate and meaningful data will be well worth the investment.