Tuesday, February 07, 2006
Mars: The Rad And Dusty Planet
"AM: What sort of answer have you found to that last question? Many people think the radiation environment of Mars is one of the main barriers to humans living on the planet.
GD:Actually, the radiation environment of Mars is less serious than the radiation of the moon, because Mars has an atmosphere. On Earth, the magnetic field and the atmosphere keep the cosmic radiation away. Our atmosphere has a shielding of about 1,000 grams per square centimeters, so there's very little radiation arriving on the Earth's surface.
On Mars, there's no magnetic field but there is an atmosphere. Because the atmospheric pressure is less than six millibars, the shielding is 60 grams per square meter. That's nearly a factor of a 100 less than Earth's, so the annual radiation dose on Mars is about 100 times more than the annual radiation dose on Earth. But there are also areas on Earth, such as in Brazil, where the natural radiation dose also is about a factor of 100 higher than usual.
Of course, the composition of the radiation is different on Mars. For instance, on Earth we have the back-scattering neutrons. But the only thing I think is a problem for people on Mars is the so-called solar flares, which are also called solar particle events. These are eruptions of the sun that blast out a high dose of radiation. To guard against these on Mars, we'll have to build shelters.
So on Mars, we will have to be careful about radiation, but there are other perimeters that I think are even more serious. One is the dust. We don't know how hazardous the dust is. We know from the Viking experiments that if you add water to the soil, you get a burst of different gases. These gases include peroxides, and that can create difficulties for astronauts if they get that in their lungs.
The dust on Mars is composed of very tiny, one-micron-sized grains -– the same size of the dust grains on the moon. The lunar astronauts said that you can not get rid of the dust; it gets into everything. So I think it's urgently required, before we send humans to Mars, for us to do a study with robots to see what happens if you gradually moisten the martian soil. I had proposed such an experiment for ExoMars, a rover of the European Space Agency, but they said it was too complicated."
Later Horneck said this about organisms exposed to UV radiation and those protected by dust.
"The organisms that are exposed outside the space station are in a dormant state, so they cannot evolve. They are just surviving. We have found that solar ultraviolet radiation is the most damaging perimeter -- it kills all organisms so far known. Except that Rosa de la Torre from Spain recently exposed lichens, and discovered that they had the same biological activity as before they were exposed to the full sunlight.
So that is something new. But we did find that if we shielded microorganisms against solar UV radiation with dust, even a dust sphere of just one centimeter, they survive pretty well in space. So that means little meteorites just one centimeter in diameter could travel for at least two weeks in space and the organisms inside would survive. I also participated in the NASA LDEF mission, the Long Duration Exposure Facility. Their microorganisms stayed in space for six years, and they also survived pretty well when they were shaded against UV radiation."
The survivability of lichen exposed to raw sunlight is an interesting discovery for advocates of Mars exploration and settlement. Also Horneck's optimism about humans being able to beat the radiation environment there is encouraging. Living underground, building shelters, and perhaps locating colonies and bases where the Martian localized magnetic fields are strongest might be a strategy for success. The power of dust to protect organisms in space is also encouraging for would-be Mars explorers. Maybe those illustrations from the Mars society that show landers covered with sandbags for radiation protection is actually a good idea. Not sandbags though: dustbags.
Technorati: space, Mars, radiation