It was one thought that Mars harbored a diverse environment capable of supporting life. “Canals” as viewed from earth through telescopes were assumed to be giant rivers spanning the planet.
It wasn’t until the 1970s that our understanding changed dramatically and we realized that it was a mostly barren wasteland.
Now, years later after the Viking probes paved the way to increase our understanding, we’ve come to the relaization that the plannet isn’t nearly as barren as we would have originally thought.
In-orbit photos (Be sure to check out the sunrise!)
Mars Surface photos