The northern and southern lights (aurora borealis and aurora australis) splash colorful lights onto the sky, aweing spectators; but this display is simply the result of a diverse distribution of charged particles streaming into the atmosphere at high speeds. The particles hit the atoms and molecules high above the Earth, exciting electrons to higher energy levels. As the electrons decay back to their original state they emit light with colors spanning the rainbow. While providing a grand light show, the northern and southern lights also demonstrate one of the remarkable ways that Earth represents a pleasant and easy place for life to thrive.
These lights happen at the North and South Poles because the planet’s magnetic field directs the particles away from the equator toward the poles. Since the atmosphere absorbs most of the particles before they strike the surface, Earth’s inhabitants are not subject to high levels of radiation pervading the universe. NASA launched the Curiosity Rover on Mars recently, and so far, scientists have been able to measure how much radiation astronauts traveling to Mars would encounter. It turns out that the level of radiation on Mars would pose significant dangers to humans and other advanced organisms.
A standard trip to Mars requires a roughly 30-month commitment. The outgoing and return trips each take 180 days (six months) to complete. The astronaut would also have to reside on the surface of Mars for 500 days (16 months) so that Earth and Mars get to favorable locations in their orbits. During the Curiosity Rover’s flight to Mars, its instruments found radiation doses of 331 mSv (millisievert). Once the rover landed on Mars, scientists were also able to estimate that 500 days on the surface would add another 320 mSv, for a total exposure of roughly 1 Sv for the round trip.1 For comparison, the Nuclear Regulatory Commission states that someone exposed to 5 Sv all at once will likely die if left untreated. Although the radiation exposure would be spread out over a two-and-a-half year period, Martian astronauts would still be exposed to 20 percent of a lethal dose.
Even more worrisome is the type of radiation encountered. Specifically, the highly energetic, high atomic number charged particles that comprise the galactic cosmic radiation (that Earth’s atmosphere channels off to the poles) are incredibly effective in causing cancer (and cancers with high mortality rates). Although the exposure for a Martian trip exceeds NASA’s safety limits, scientists are investigating ways to mitigate the radiation effects. For example, while on Mars, the astronauts could remain underground where the soil provides a shield against radiation. Perhaps more importantly, in learning to mitigate the effects of radiation for space travel, scientists may learn how to better treat cancer patients inhabiting Earth!
The desire to explore our neighboring planet reveals two important facts. First, as we understand the risks of traveling to Mars, we also learn how to better care for all of humanity. Second, the dangers of long-term space travel show the phenomenal capacity of Earth to support life. Occasionally, we get to see spectacular displays of light, reminding us of these two important points.
- Donald M. Hassler et al., “Mars’ Surface Radiation Environment Measured with the Mars Science Laboratory’s Curiosity Rover,” Science 343 (January 2014): 1244797, doi:10.1126/science.1244797.