Astronauts on long-term space missions may face health risks that their predecessors didn't have to worry about. These Science Update reports describe two of them.
1. Space Radiation
Cancer concerns for astronauts. I'm Bob Hirshon and this is Science Update.
Long-term human space travel, like a mission to Mars, presents many challenges. One of them may be an elevated risk of cancer. Scientists at Georgetown University's Lombardi Comprehensive Cancer Center have been studying mice exposed to the kind of high-energy radiation found in space: radiation that Earth's atmosphere screens out for us. Those mice got lots of cancer-linked free radical chemicals in their digestive tracts. Biochemist Albert Fornace says the next step is to find out how this may affect cancer rates in astronauts.
And then of course, a longer term issue is are there preventative agents that could be used that would reduce their risk?
Unfortunately, he says it's not as simple as building a radiation shield on the craft, since such a shield would have to be too dense to launch into space. I'm Bob Hirshon for AAAS, the Science Society.
2. Lunar Dust
Could moon dust threaten astronauts? I'm Bob Hirshon and this is Science Update.
Some workplaces, like coal mines and oil refineries, pose a danger to workers' lungs. Now, scientists are trying to find out if the moon should be added to that list. Pulmonary physiologist Kim Prisk, of the University of California at San Diego, says lunar dust sticks to the spacesuit like sand on a bathing suit.
And there were many comments, in fact, during the Apollo missions, from the crews, about how pervasive this dust is and how much of it got into the crew module.
Those trips were short, but future moon missions may go on for months. What's more, Prisk says that lunar dust particles have worrying similarities to known lung toxins, and that low gravity may help them penetrate the lungs more deeply. He and his colleagues will try to determine what the risk to astronauts may be, and how to minimize it. I'm Bob Hirshon for AAAS, the Science Society.
Making Sense of the Research
When you get an X ray at the doctor or dentist's office, you might notice that the technician stands outside the room to turn on the machine. It's a little unnerving: why does she have to protect herself from something that's supposed to help you? The answer is simple: you might get an X ray once a year, if that, while an X-ray technician may take dozens of X rays in a day. So in order to prevent over-exposure, the technician avoids all X rays—unless, of course, she herself is the patient.
That illustrates a basic principle of risk assessment in public health: when someone is exposed to a potentially hazardous substance, the frequency and duration of exposure weighs heavily in determining the health risk. To give another example, consider asbestos, a name for a group of fireproof minerals that has long been used in construction, shipbuilding, and car manufacturing. It's now known that asbestos particles cause lung cancer and other diseases. Although asbestos has been banned in many countries and removed from many buildings, the people most at risk for asbestos-related disease aren't those who simply lived in buildings with asbestos insulation, but workers who directly handled the material on a daily basis as part of their job. Those workers would be most likely to have inhaled a large number of asbestos particles over a long period of time.
These two reports describe potential health risks that the next generation of astronauts may face, because they will spend much longer periods of time in space and/or on the moon. Although three Russian cosmonauts spent 438 continuous days on the space station Mir in the mid-1990's, most astronauts' trips have been far shorter, lasting only a few days, hours, or even minutes. Therefore, the potential long-term impact of the space environment on astronaut health hasn't been as relevant as it will be on future missions. And even if astronauts in the past have suffered some kind of elevated health risk from their short space trips, it's hard to know that for sure, because the number of people who have ever been in space is too small to yield strong statistics.
In the case of radiation, today's models of health risk are based on a person's total amount of exposure over the course of a lifetime. However, the models assume exposure only to the kinds of radiation people encounter here on earth. Fornace's team is trying to find out if high-energy radiation from space is more toxic, dose for dose, than earthly radiation. His experiments with mice give reason for concern, because the damage caused by exposure to high-energy radiation was different, and worse, than the damage caused by an equal dose of low-energy radiation.
In the case of lunar dust, Prisk's work is just getting underway, but he cites several reasons to worry about the dust. First, as the report mentions, it gets into everything, so if it is toxic, the exposure level could be very high. Second, it has a jagged crystal structure that resembles fresh-fractured quartz, a toxic earth mineral. Third, in a low-gravity environment, small dust particles tend to penetrate more deeply into the lungs than they would normally, and deep lung tissue isn't as well equipped to neutralize toxic particles. To assess the potential risk to astronauts, researchers will conduct two types of experiments: lab studies on lunar dust itself and its effects on cell samples, and human studies in which volunteers inhale non-toxic particles during low-gravity flights on NASA aircraft. Only after years of research will scientists be able to estimate how much danger these and other environmental factors pose to astronauts.
Now try and answer these questions:
- Why is it more important to consider issues like space radiation and lunar dust than it was in the past?
- What kind of space radiation are scientists worried about? What is the evidence that it may be a health hazard? What has yet to be determined?
- What characteristics of lunar dust are raising concerns? What has yet to be determined?
- Can you think of other examples of health risks that increase with exposure to a particular environment?
You may want to check out the June 20, 2008, and May 2, 2008, Science Update Podcasts to hear further information about these Science Updates and the other programs for these weeks. These podcasts' topics include: Journeys in Time and Space (satellite archaeology reveals Mexico's past, Magellan's unusually benign weather, threats to lunar astronauts, and a telescope that can see invisible dark matter) and Radiation (the world's most powerful laser, radiation dangers for astronauts, a new drug fights radiation poisoning, and the lifespan of the sun).
The National Geographic News article Shuttle's Human Experiments Pave Way for Moon, Mars Voyages describes other experiments underway in preparation for long space flights.
The article Space Weather Could Scrub Manned Mars Mission describes the solar storms that produce potentially hazardous space radiation.