Editorial [Hot Topic:Traveling Space: Biological Considerations, and the Benefits for Terrestrial Medicine (Guest Editor: H. Hinghofer-Szalkay)]

Human exploration of space raises plenty of questions regarding physiological changes within the body subjected to a new and foreign environment. Nearly every component of the human body is affected. During microgravity conditions, the almost complete reduction in weight of all its components, plus exposure to heightened levels and different types of radiation may work together to increase risk during space travel. Still, the difference between 'Spaceflight' and 'Earthbound' Medicine is not as big as it looks. The basic biological principles are the same, no matter what particular condition of travel we are subjected to. And travel it is: We are on a galactic journey, eternally in motion. Earth is nothing less than a great spaceship, complete with a functioning and stable life support system (the only reliably functioning one we know of) that, incidentally, we might be in the process of jeopardizing right now. Human space exploration is important for several reasons, one being that it works as an eye-opener, showing our home planet from above and demonstrating its beauty and fragility. At the end, this might be more important than hundreds of 'spin-offs' from spaceflight research and development. Psychological effects (confinement, isolation, boredom, lack of leisure perspectives, etc); effects of radiation; and effects of changed gravitational environment (microgravity during ballistic phases, hyper-G during launches, aerobraking or landing) are the main problem drivers of human space flight. Humans have proven they can spend long time periods in space without obvious biomedical complications (up to 14 months as current world record: Valery V. Polyakov, M.D.). However, extended duration flights, as human missions to Mars, will pose bigger difficulties: Higher radiation dose, increased feeling of isolation and no immediate return option, longer absence of Earth-like gravitational pull, with possible aggravation of deconditioning phenomena. While the latter point could be resolved using artificial gravity, there is no way to avoid solar and cosmic radiation (with the exception of shortterm stay in 'safe havens') and to reliably counter potential psychological complications. However, compared with a multitude of occupational high-risk environments, it seems that human travel to Mars does not constitute an unusually high jeopardy to crew health and performance. From a medical point of view, adaptation capabilities seem sufficient to deal with foreseeable challenges of such an endeavor. It is important to understand that gravity governs the organization and function of all life in the biosphere. Organisms are continuously under gravitational influence, which shapes their anatomy and physiology. The biological consequences and implications of long-term alteration of our gravitational environment are unknown. Human exploration of the Moon, Mars, and other destinations in our solar system will stimulate scientific breakthroughs and spawn new medical paradigms. This intellectual 'spin-off' will prove to be amongst those things that last in history.