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B "Without Earth's atmosphere, cosmic rays would be lethal"

  1. Apr 27, 2016 #1
    In the episode Unafraid of the Dark in Neil deGrasse Tyson's series Cosmos, Tyson says the following: "Hess had discovered cosmic rays, showers of subatomic particles that crisscross the universe at nearly the speed of light. Without the shielding effect of the Earth's atmosphere, they would be lethal. Some cosmic rays can carry as much energy as a bullet fired from a rifle." If that's true, how did the astronauts who walked on the moon survive? They weren't shielded by the Earth's atmosphere, and the moon does not have an atmosphere to shield them. I know that the astronauts wore those space suits that covered their entire bodies, but I don't think that such space suits were bulletproof.
     
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  3. Apr 27, 2016 #2
    They would be lethal long term. The Apollo astronauts did get pelted with Cosmic rays. Every single one of them reported instance of bright flashes within their capsule. It was determined that these were cosmic rays hitting the back of their eyes. Humans can stand some radiation, we just can't stand very much of it for very long. If the sun decided to throw a tantrum at exactly the wrong moment, and the astronauts got hit by a solar flare, it would have killed them very quickly.
     
  4. Apr 27, 2016 #3
    When Neil Tyson spoke of cosmic rays that were lethal, I don't think he was talking about cosmic rays from the sun. I think he was talking about cosmic rays from Supernovas and neutron stars.
     
  5. Apr 27, 2016 #4
    Not if Dr Tyson was saying that the Earth's magnetic field is what protects us from them. The Sun protects us from those with it's steady outwards solar wind. Cosmic rays of that type should only reach Earth if they're so powerful that they push the sun's entire heliosphere back to the orbit of the Earth. If rays hit that are that intense, our tiny little magnetosphere will barely provide any protection.
     
  6. Apr 27, 2016 #5
    newjerseyrunner, if Tyson meant that Earth's magnetic field is what protects us from cosmic rays, he would have said Earth's magnetic field is what protects us from cosmic rays, not that Earth's atmosphere protects us from cosmic rays.
     
  7. Apr 27, 2016 #6

    Vanadium 50

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    Tyson is overstating the case a bit. The atmosphere protects us from most but not all of the cosmic rays - the average total exposure would perhaps triple. If it weren't there, more people would die (especially from gasping for breath), but not from acute radiation: mostly long term cancers. I'd be more worried about backscattered neutrons from the earth than the cosmic rays themselves.
     
  8. Apr 27, 2016 #7
    There are two major sources of radiation, solar and cosmic (meaning from beyond the solar system). Solar radiation obviously originates with the sun, and we can detect that (to an extent) in advance. Cosmic radiation, however, can come from any direction, and is impossible to detect in advance. Both could prove fatal to unprotected astronauts. Even in 1969 they knew the effects of solar radiation could prove fatal. The astronauts were very lucky, and it also explains in part why there have been no manned-missions beyond the protective magnetic field of Earth since 1973.

    Even in the protective magnetosphere of low-earth orbit, the astronauts on the ISS are still exposed to "5 to 12 μ Gy (0.5 to 1.2 milli rads) per hour" which equates to "44 to 105 milli Gy (4.4 to 10.5 rads)" annually. That is 11.5 ± 4 times the background radiation we experience on the surface of the planet in the US. The NASA source below also has numerous other publications which can be referenced concerning both solar and cosmic radiation in space.

    On the surface of Mars the daily radiation dose ranges from between 200 to 220 μ Gy per day, or 12 ± 0.5 times higher than the normal background radiation on the surface of Earth in the US. That is not a large enough dose of radiation to prove fatal, it is very close to what astronauts currently experience on the International Space Station. Mars offers no protection from solar or cosmic radiation spikes. With sufficient warning, astronauts could get to a protective shelter in the event of a solar flare or coronal mass ejection. However, there is no way to warn the astronauts about an impending spike in cosmic radiation, for example, from a gamma-ray burst.

    Solar and cosmic radiation is certainly one of the biggest technological challenges we have to face in our exploration of manned space missions.

    Sources:
    Deadly Solar Flares Pose Threat To Astronauts While On Moon - Daytona Beach Morning Journal, July 15, 1969
    International Space Station Internal Radiation Monitoring (ISS Internal Radiation Monitoring) - NASA, International Space Station Mission Pages
    Radiation Measurements on Mars - NASA/JPL, from August 2012 to June 2013
    Background Radiation - Wikipedia
     
  9. May 6, 2016 #8
    But keep in mind that natural background radiation on Earth is quite variable from place to place. There are lots of places where it is x3 Earth average. There are rare places where it is x100.

    If LEO is x11 and Mars is x12, those levels are actually okay for humans.
     
  10. May 6, 2016 #9
    I did indeed keep that in mind, which is why I stated "the background radiation we experience on the surface of the planet in the US." The background radiation in the US is about twice that of the world-wide average. Eleven to twelve times the background radiation of the US is most certainly not "okay for humans." It isn't fatal, but hardly "okay." There is also the problem of leaving Earth's protective magnetic field:
    We were very lucky not to lose any of our astronauts to solar or cosmic radiation between 1969 and 1973. Solar and cosmic radiation will be a serious consideration and technological challenge on any future manned missions beyond Earth's protective magnetosphere.
     
  11. May 7, 2016 #10
    From what I read below, ~12 μGy/h indeed is okay.

    https://en.wikipedia.org/wiki/Background_radiation

    Areas with high natural background radiation

    Some areas have greater dosage than the country-wide averages. In the world in general, exceptionally high natural background locales include Ramsar in Iran, Guarapari in Brazil, Karunagappalli in India, Arkaroola in Australia and Yangjiang in China.

    The highest level of purely natural radiation ever recorded on the Earth's surface was 90 µGy/h on a Brazilian black beach (areia preta in Portuguese) composed of monazite. This rate would convert to 0.8 Gy/a for year-round continuous exposure, but in fact the levels vary seasonally and are much lower in the nearest residences. The record measurement has not been duplicated and is omitted from UNSCEAR's latest reports. Nearby tourist beaches in Guarapari and Cumuruxatiba were later evaluated at 14 and 15 µGy/h.

    The highest background radiation in an inhabited area is found in Ramsar, primarily due to the use of local naturally radioactive limestone as a building material. The 1000 most exposed residents receive an average external effective radiation dose of 6 mSv per year, (0.6 rem/yr,) six times the ICRP recommended limit for exposure to the public from artificial sources. They additionally receive a substantial internal dose from radon. Record radiation levels were found in a house where the effective dose due to ambient radiation fields was 131 mSv/a, (13.1 rem/yr) and the internal committed dose from radon was 72 mSv/a (7.2 rem/yr). This unique case is over 80 times higher than the world average natural human exposure to radiation.

    Epidemiological studies are underway to identify health effects associated with the high radiation levels in Ramsar. It is much too early to draw statistically significant conclusions. While so far support for beneficial effects of chronic radiation (like longer lifespan) has not been observed, a protective and adaptive effect is suggested by at least one study whose authors nonetheless caution that data from Ramsar are not yet sufficiently strong to relax existing regulatory dose limits.
     
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