Dangers of space exploration
Exploration is an important survival strategy in evolution. The migration of expansive species depends on exploring their immediate or distant surroundings for new food sources or safe habitats; it can also come as a result of population pressures or environmental changes. The human species has added another reason for exploration, namely curiosity. This intellectual urge to explore the unknown led the great European explorers to the Americas, Australia and Antarctica between the fifteenth and seventeenth centuries. Inquisitiveness about nature is also the driving force behind humans exploring the polar caps, climbing mountain peaks and diving into the abysses of the oceans. Now, the ultimate frontier to explore in the twenty-first century is space. Astronomical observations and satellites have already yielded immense knowledge about our solar system and the universe beyond. But these technologies can provide only a limited picture of what is out there; eventually humans themselves will have to travel to other planets to investigate them in more intimate detail. Tremendous advances in rocket and spaceship technologies during the past 50 years, driven mainly by national security considerations, the need for better communication or a desire to observe environmental changes and human activity on the ground, have made it possible to send humans into near-Earth orbit and to the Moon. Conceivably, these advances will eventually make it possible to transport astronauts to other planets, and Mars in particular.
Late spring on Mars. Source: NASA.
But there are significant differences between exploring Earth and exploring space. First and foremost, space is an unforgiving environment that does not tolerate human errors or technical failure. For humans leaving Earth's orbit for extended periods, there are even more dangers. One is the near absence of gravity in space; the presence of high-energy, ionizing cosmic ray (HZE) nuclei is another. Because both zero gravity and cosmic rays would have severe health implications for astronauts on a Mars-bound spaceship, we first need to investigate their effects on cells, tissues and our hormonal and immune systems. However, although we are able to produce HZE nuclei on Earth and study their effects on biological material, we cannot simulate extended periods of low gravity and their additive effects on cells and tissues. Thus, the International Space Station (ISS) will have an enormously important role in assessing the health dangers for humans in space and in the development of potential countermeasures.
There is much information on the adaptation of astronauts to zero gravity (0g) in space and on their return to 1g on Earth. Nevertheless, our understanding of these effects is not complete; nor have countermeasures to mitigate them been identified.
As both zero gravity and cosmic rays would have severe health implications for astronauts on a Mars-bound spaceship, we first need to investigate their effects on cells, tissues and our hormonal and immune systems
Observations of astronauts travelling on the Space Shuttle and Russian cosmonauts' long-term visits to the Mir space station indicate that time spent in 0g has serious effects on bone and muscle physiology and the cardiovascular system. For instance, the return from 0g to 1g leads to an inability to maintain an appropriate blood pressure when in an upright position—orthostatic intolerance—and insufficient blood flow to the brain. Astronauts returning from orbit therefore have to rest for several minutes, and the time needed to normalize their blood pressure increases with the time spent in 0g. This could mean that astronauts travelling to Mars—which would take at least one year in 0g—would need considerable time to readapt to gravity after landing there or after their return to Earth, unless we find a technological solution to the creation of artificial gravity on a spaceship. Moreover, there are other cardiovascular effects, such as cardiac arrhythmia and atrophy, that need to be studied in more detail before we can ensure the safety of astronauts on a Mars mission. Other effects of extended time in low gravity are loss of bone mass and muscle deterioration. Without adequate countermeasures, these could impair the ability of astronauts to perform necessary functions on a spacecraft or on the surface of Mars.
The second main danger for human travellers is the presence of the aforementioned HZE nuclei in cosmic rays, because of the ionizing effect that they exert on atoms or molecules. Although they do not reach the Earth's surface because they are either absorbed by the atmosphere or deflected by Earth's magnetic field, there are already some experimental data on the cancer-inducing properties of electrons, neutrons and protons in cosmic rays and other potential deleterious effects on biological material from numerous Earth-based experiments on laboratory animals. In addition, studies of the effects of the atomic bombs dropped on Japan in 1945 pro-vided further data about the health dangers of radiation and high-energy nuclei.