NASA announced earlier today that liquid water was discovered on Mars. For decades there has been speculation that there was water some indeterminate time in the past and that it was all gone. People speculated that other factors were at play with what appeared to be (and in fact are) features that change seasonally (remember, Mars has seasons because of its tilted axis just like the Earth does). Well, now there's no hedging bets, there absolutely is liquid water on Mars.
Hydrated salts were discovered in the Hale crater in dark streaks that change with the seasons. In the Martian Summer the ice melts and forms salt water streams that refreeze in the Winter. The high salinity keeps the water liquid at temperatures well below its freezing point. The minerals in the water are mostly magnesium perchlorate, magnesium chlorate, and sodium perchlorate.
Water, so far as we know, is a necessary condition for life, and even though that water contains strong oxidisers, who knows, there may be life on Mars. Those microscopic fossils might just be the tip of the iceberg.