For many years astronomers observing Mars have been intrigued by dark streaks that appear and disappear through the Martian year. Now they've measured the chemical make-up of these streaks and found various salts.
Because salty water can remain liquid at lower temperatures, there could be trickles of water on the freezing-cold surface of Mars - a fascinating thought. This means bacteria could be living there right now.
I believe this is one of those small steps that may lead to a giant leap in understanding the cosmos.