NASA says ‘dark finger-style’ marks that change with the seasons and were first spotted in 2011 by Ojha, using images taken by the Mars Reconnaissance Orbiter, are signs of water flowing under the surface of Mars. Ojha investigated the composition of these seasonal flows by studying their infrared wavelengths. In each location researchers found the presence of hydrated salts during the times when the flows are most extensive – suggesting a link between the two. In particular, evidence was found for sodium perchlorate, magnesium perchlorate and magnesium chlorate which are thought to be left behind when brine evaporates. Ohta:
The only thing we can really assert is that the places we’re finding are probably more habitable than the rest of the planet, which is bone dry.