Dark streaks known as recurring slope lineae (RSL) grow up to a few hundred meters in length and are formed by briny liquid water. These streaks lengthen and get darker in the warmer months and fade away in the cooler parts of the year. For years it has been hypothesized that they were created by water but there was no evidence until now. Spectrometer observations of the RSL show signatures of hydrated salts which confirm the hypothesis.
We are still in our infancy understanding the universe... even those bodies closest to us leave us dazzled.
Recently, there was an image sent back from MSL Curiosity of something that looked crab-like but... it was immediately dismissed as pareidolia. If that same image had been from our world, it would have never been called, a 'rock'.
We won't really know if we don't go.
Sidenote: NASA has been promising a manned mission since the end of the Apollo program but each time we got close to their officially released dates, they kicked it back over the horizon.
I know I will never live to see it happen.
...
btw the crab-thing was exactly that... a rock... just like every other non-earth exotic has proved to be so far.