When the Mariner 6 and 7 probes flew by the Red Planet just weeks
after the Apollo 11 mission and showed there were no canals in their
far images, which were unblurred by Earth's distance and atmosphere.

The probes did image Valles Marineris and Olympus Mons, but they
were not recognized for what they were until Mariner 9.

See the December, 1967 issue of National Geographic Magazine with
the article on Mars by Carl Sagan. Life right up to animal form was
still seriously considered a possibility. The canals were considered
to be possible natural features (Mariner 4's less than stellar 22 images
left a lot open regarding just what was on the face of Mars besides
a lot of craters). The Viking mission was still known as Voyager. And
we were supposed to have landed men on Mars sometime in the 1980s.

Even though there were some prominent astronomers who questioned
the very existence of the infamous canals, try and find artwork of the
Red Planet up through the early 1960s - especially the ones showing
spaceships over the planet - that did not show Mars with its canals.
They do exist, but they are far less common.

So don't be too harsh on your 3rd grade teacher. Even the pros might
have agreed with her.

And in some ways it is too bad that Mars wasn't exactly what we
thought and hoped it would be. A good part of the reason we don't
have humans on the Red Planet is due to what the first Mariners
revealed (and did not reveal) about that alien world.