...the whole point of Mars aka Lowell was for it to be a bit more like Earth, maybe without the canals - though astronomers who saw the 'canals' didn't all think they were artificial. Some thought they were like the 'rays' from Luna craters, but actual cracks in the crust. Ernst Opik predicted years before Mariner 4 that Mars would have more craters than Earth, lots more because of the lower erosion and proximity to the Main Belt.

Lowell said the surface pressure on Mars was about 0.085 bar and even up until the early 1960s that's what the best estimates concluded based on photometry - and it would've been right if it wasn't for the dust! But the dust made the atmosphere look denser than it was. That 0.085 bar would've made landing von Braun's winged Mars-planes easy and would've made Phil Bono's single-launch Mars-mission doable. It would've meant walking around in the deep parts of Hellas Planitia in just oxygen masks doable and temporary salty lakes around the Poles would've been stable.

But it was not to be.

And don't get me started on Venus...