The notion of water on Mars preceded the space age by hundreds of years.
Early telescopic observers correctly assumed that the white polar caps and clouds were indications of water's presence.
Thus, many secondary minerals do not actually incorporate water, but still require water to form.
Some examples of anhydrous secondary minerals include many carbonates, some sulfates (e.g., anhydrite), and metallic oxides such as the iron oxide mineral hematite.
Furthermore, the variations in the radio signal from the spacecraft as it passed behind the planet allowed scientists to calculate the density of the atmosphere.
The man most responsible for popularizing this view of Mars was Percival Lowell (1855–1916), who imagined a race of Martians constructing a network of canals to bring water from the poles to the inhabitants at the equator.These observations, coupled with the fact that Mars has a 24-hour day, led astronomer William Herschel to declare in 1784 that Mars probably offered its inhabitants "a situation in many respects similar to ours." By the start of the 20th century, most astronomers recognized that Mars was far colder and drier than Earth.The presence of oceans was no longer accepted, so the paradigm changed to an image of Mars as a "dying" planet with only a meager amount of water.Thus, a vision of Mars was born of a world much like the Moon, but with just a wisp of an atmosphere to blow the dust around.This view of Mars would last nearly another decade until Mariner 9 showed a much more dynamic Mars with hints that the planet’s past environment was more clement than the present one.