"Today's Mars is dry and probably has been that way for 2 billion years, but at one time Mars was shaped by water," said Ashwin Vasavada, NASA's deputy project scientist for the Mars rover Curiosity. "Rivers, lakes and ground water were present for millions of years. The atmosphere must have been thicker. Mars must have been warmer... and the climate system must have been loaded with water."
Mars at one time had the right ingredients and the right environment to support life, even if only in microbial form.