Radiation
Natural Radiation on Mars is much higher compared with Earth. The thin atmosphere provides only a small shielding effect against harmful solar radiation and cosmic radiation. Mars also lacks the magnetosphere that protects Earth.
Occasional solar flares produce particular high doses. Some solar proton events (SPEs) were observed by MARIE that were not seen by sensors near Earth due to the fact that SPEs are directional. Astronauts on Mars could be warned of SPEs by sensors closer to the Sun and presumably take shelter during these events. This would imply an Early Warning System (possibly a network of sensors in orbit around the sun or a single sensor in Lagrangian point L1) might be needed to ensure all SPEs threatening Mars were detected early enough.
Contents
Types of Radiation
Radiation comes in a variety of forms:[1]
| Name | Relative Biological Effectiveness RBE |
Source |
|---|---|---|
| X-Rays and Gamma Rays | 1 | Radiation belts, solar radiation, and bremsstrahlung electrons |
| Electrons 1.0 MeV |
1 |
Radiation belts |
| Protons 100 MeV |
1-2 |
Cosmic rays, inner-radiation belts, and solar cosmic rays |
| Neutrons 0.05 ev (thermal) |
2.8 |
Nuclear interactions in the sun |
| Alpha Particles 5.0 MeV |
15 |
Cosmic rays |
Danger
Exposure to dangerous levels of radiation causes radiation sickness and cancer. Any exposure to radiation, no matter how slight, poses some risk. Small dose - small risk of cancer. High dose - high risk of cancer.
Nevertheless, there are defined legal limits for exposure during work for several professional activities, such as for X-ray assistants, airplane personnel, etc. The International Commission on Radiation Protection recommends that occupational (work-related) radiation exposure be limited to 50 millisieverts (mSv) per year, and limited to 100 mSv over any 5-year period[2].
The equivalent dose rate from cosmic radiation on Earth's surface at sea level is 0.26 mSv per year[3]. Based on measurements made by the Curiosity rover, the corresponding figure for the surface of Mars is approximately 230 mSv/year[4]. Curiosity also measured the temporary increase in radiation during a single SPE. The results indicate an increase in equivalent dose rate of approximately 25% over a 1-day interval[4]. This figure will vary depending on the intensity of a particular SPE.
Effect on material
Radiation can change the properties of plastics and metals, making them brittle after a period of time.
Protection
Houses should be equipped with a radiation shielding, thick enough to reduce the radiation to a level equal to Earth, that is, almost zero. Best protection may be achieved with houses built in natural caves or set into cliffs or hillsides.
Space suits must be designed with radiation in mind. The suit should provide adequate shielding for the occupant. It may be necessary to design suits with several grades of protection. Suits designed for short-term use can carry lighter shielding which would reduce weight and improve maneuverability.
During severe radiation events, such as solar flares, surface settlements may use storm shelters with heavier than normal shielding.
Open issues
- How much higher is the UV and cosmic radiation?
- What is the required thickness of a regolith or water layer upon a house for radiation shielding?
- What are the legal limits for radiation exposure for some professional activities?
- Does regolith emit an own portion of radiation, some kind of secondary radiation due to the long exposure to cosmic and solar radiation?
