The solar wind is the continuous stream of energetic and ionized particles from the Sun that extends far into interplanetary space following the interplanetary magnetic field (IMF). The solar wind strongly interacts with magnetic fields of the planets and will often manifest itself as aurorae in the upper atmospheres of planets with magnetic fields. The solar wind is often associated with Coronal Mass Ejections (CMEs), solar flares and coronal holes.
The normal solar wind is little danger, but a CME is deadly dangerous. CME typically happen a couple times a year, so the plans to shield against radiation are concerned with handling CME's.
In the case of Mars, with a weak (often considered to be non-existent) global magnetic field, solar wind particles have greater penetration into the atmosphere, creating a hazard to any future human settlements on the surface. Like every other radioactive radiation it causes damage to material and health.
Note that the solar wind consist of the following particles: electrons, protons, and alpha particles (helium nuclei). This is bad (they are all forms of ionizing radiation), and good (this type of radiation is much easier to shield against, than gamma rays).
The solar wind is characterised as a constant flow of plasma from the chromosphere into interplanetary space. Understood to be bi-modal, the solar wind consists of two distinct streams. The fast solar wind travels at velocities of between 700-900 km/s and is associated with open magnetic flux (i.e. coronal holes located in solar polar regions). The slow solar wind travels at velocities of between 300-400 km/s and is located above equatorial closed magnetic flux regions (i.e. the streamer belt).
Effect on Mars
It is believed that the solar wind is responsible for the atmospheric loss of one third of Mars' atmosphere into space. Partly due to the Martian atmosphere's inability to retain its atmospheric gases due to the lack of a planetary magnetic field and the sheer voracity of the flow of ionizing solar wind particles, the solar wind is a major culprit for the low atmospheric pressure measured at the surface.
Artificial magnetic field
The threat from solar wind can be managed through the generation of local magnetic fields. Recent research has shown that the size of the field need only be several hundred meters wide to provide protection to humans in space. This magnetic shield could be scaled up to protect an entire settlement on the surface.
While shielding a space ship increases its mass and fuel consumption, the shielding of a Martian colony is much easier, since the mass is only limited by structural stability constraints. Space craft will likely have a 'storm shelter', a small volume where there is much higher radiation protection. The crew will have to crowd inside the storm shelter for the duration of the solar storm (~3 hours). Small ground bases can either use this storm shelter, or use local resources (such as water or sand bags) to increase the radiation protection for the entire habitat.
- "Solar Plasma Experiment" by Neugebauer & Snyder, Science, Volume 138, Issue 3545, pages 1095-1097, 1962
- "Origins of the Slow and the Ubiquitous Fast Solar Wind", Habbal et al., Astrophysical Journal Letters v.489, page L103, 1997
- The interaction of a flowing plasma with a dipole magnetic field: measurements and modelling of a diamagnetic cavity relevant to spacecraft protection. R Bamford et al 2008 Plasma Phys. Control. Fusion v.50, Issue124025 Pages 1-11
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