Because Mars lacks a magnetic field, the Sun’s solar radiation may stymie attempts to create an atmosphere on the red planet.
Scientists have discovered that our Sun’s solar radiation may thwart all attempts at increasing the atmospheric pressure of the crimson world, which means we may never get the chance of witnessing a green Mars, let alone a blue one.
(Discovery News) Scientists have identified a sort of double-whammy solar super wave that is responsible for blowing away air from Mars and keeping its atmosphere thin, frigid and downright inhospitable for any possible future travelers.
The waves happen when one stream of solar wind is overrun and amped up by another, faster gale of solar particles. That creates a flying traffic jam of particles that slam into Mars as one large pulse. [...]
When Edberg and his colleagues compared these events at Mars to the flow of heavier atoms blowing past Mars Express, they discovered that fully a third of Martian air loss happens during the 15 percent of the time when doubled-up solar wind pulses hit the planet.
Although this means that Mars may never become a second eden (unless we can create a global magnetic field), it does not mean that humanity will never settle the planet en mass.