Here is some info on the models that NASA has come up with which display a much different planet than we know todaY:

Now, new isotopic measurements by NASA researchers reveal that an ocean once covered approximately twenty percent of the Martian surface. This new picture of early Mars is considerably wetter than many previous estimates, raising the odds for the ancient habitability of the Red Planet.

Commenter Daniel had this inquisitive comment:

I wonder how much water is actually locked away in ice? I’m doubtful of terraforming considering Mars’s core is frozen solid therefore no electromagnetic shield to protect any atmosphere we could create.

The Mars pics from NASA’s mission in 2015 have been awesome and we’re looking forward to more as they come in.