Mars is the 7th largest planet in our solar system that, since the 1960s, has been robotically explored more than any other planet beyond Earth.
Mariner 9 imaging in 1971 revealed the first direct evidence of water on the Red Planet. Yet only thanks to the recent ESA ExoMars and Mars Express missions was water frost spotted for the first time near Mars’s equator, a part where it was thought impossible for frost to exist.
More info: Nature Geoscience