In a study that even made it to the prestigious American science magazine Science, it is stated that a trip to Mars increases the risk of cancer by 3%. Is this story correct and are the authors of the article aware of the latest scientific research in this area? An analysis.
'Trip to Mars increases cancer risk'
In the article in question, Measurements of Energetic Particle Radiation in Transit to Mars on the Mars Science Laboratory , and the Science Podcast interview , describe observations of cosmic rays. These were carried out by the Radiation Assessment Detector (RAD) instrument on board the Mars robot, Curiosity, during its journey to Mars. The shield around the RAD , consisting of the spacecraft wall and the surrounding robot, is broadly similar to the shield used in manned spacecraft. These measurements therefore give a good idea of the radiation that astronauts on board a spacecraft will experience on their way to Mars, the researchers said. It seems impossible to get a pin in between. But is everything said with this? No, as an unexpected discovery from a few years ago proves.
In the vacuum of space, there are two sources of radiation that are of concern to space experts. These are the solar wind and the galactic cosmic rays. The sun scatters large amounts of fast-moving ions, mainly protons and helium nuclei, which are a major radioactive problem. On Earth, we are not bothered by this because the strong earth's magnetic field deflects the solar wind and the thick atmosphere completely absorbs the remaining particles. In 2010 it was discovered that even a fairly weak magnet is already able to deflect a fast-moving plasma current, such as the solar wind, for example. The reason is that not only magnets, but also moving particles generate a magnetic field. The magnetic fields repel each other, creating a strong deflecting force on the particles (Maxwell's third equation). All the concerns that space experts had about the solar wind turned out to be unnecessary . Presumably, by applying a reasonably weak magnetic field, an important part of the measured radiation, namely the solar wind, can be switched off quite easily.
Galactic cosmic rays
A bigger concern is the cosmic rays emanating from the rest of the universe, mainly from the Milky Way of which we are a part. Unlike the solar wind, these particles come from all directions. Their magnetic fields therefore cancel each other out, so that the plasma effect will occur very weakly or even not at all.
Galactic cosmic ray 1% consists of very hard X-rays, with energies per photon sufficient to form small atoms. These are forms of electromagnetic radiation and can only be stopped by radiation shields that are meters thick. 1% isn't very much, though. The damage caused by this radiation remains relatively limited.
The remaining 99% consists of electrically charged particles, mainly (90%) protons and (9%) helium nuclei. The rest consists of heavier atomic nuclei. Given a certain magnetic field strength and charge, charged particles in a magnetic field will describe circles with a certain diameter, depending on the ratio between mass times speed divided by charge times field strength.
To be precise:
Interestingly, the number of revolutions per second for these circles is independent of speed. If these circles are far enough from the spaceship, the occupants are safe.
Unfortunately, relativistic effects now throw a spanner in the works. The particles are extremely energy-rich and move almost at the speed of light. This leads to a strong increase in their mass, to be precise with the Lorentz factor γ:
Increased risk of cancer?
According to calculations by , the risk of cancer would increase by approximately 3%. The greatest radiation exposure, approx. 60%, comes from solar wind, which can be blocked by means of a fairly weak magnetic field. Currently, there is about a 3% chance of an astronaut being killed in a space flight, making an astronaut a more dangerous job than, say, a soldier in the US military. In percentage terms, this means that far fewer astronauts will die from diseases of old age such as cancer than normal people.
1. C. Zeitlin et al., Measurements of Energetic Particle Radiation in Transit to Mars on the Mars Science Laboratory, Science, 2013
2. Transcript Science Podcast 31.05.2013
3. C. Zeitlin et al., The Radiation Assessment Detector (RAD) Investigation, Space Scientific Review (2012)
4. R Bamford et al, The interaction of a flowing plasma with a dipole magnetic field: measurements and modeling of a diamagnetic cavity relevant to spacecraft protection, Plasma Phys. Control. Fusion, 2008
5. Siddharth Raval, Superconducting Magnets to Protect Spacecraft from Radiation, Space Safety Magazine, 2013