If Mars is ever to be terraformed for human colonization, what is likely going to be the first step in that process? Hint: You cannot do anything regarding terraforming until liquid water is stable on the surface.

Mars lacks a magnetosphere, which poses challenges for mitigating solar radiation and retaining atmosphere. It is thought that the localized fields detected on Mars are remnants of a magnetosphere that collapsed early in its history.

The lack of a magnetosphere is thought to be one reason for Mars's thin atmosphere. Solar-wind-induced ejection of Martian atmospheric atoms has been detected by Mars-orbiting probes. Venus, however, clearly demonstrates that the lack of a magnetosphere does not preclude a dense atmosphere