I'm not a big fan of science fiction. I find "real" science to be generally more interesting; the fictionalized kind usually requires me to pretend that the universe is far different than what I believe to be the case. In fiction, travel between planets (or even solar systems) is accomplished quite easily, by suspension of the speed limit imposed by relativity. Real exploration of Mars is now under increasingly serious discussion, and Jerome Groopman has written a stark description of the medical challenges that would have to be surmounted for such an expedition to be successful. Will the astronauts of the future be able to walk on Mars, after six months or more of weightlessness? What happens to an astronaut who suffers a bleeding ulcer, appendicitis, or a broken limb? Will older explorers (whose families are complete) be chosen because cosmic radiation would likely damage DNA? The psychological consequences of living in close quarters, under stress, uncertainty, and isolation could prove to be even more damaging than the physical hazards. Are the risks worth it?