Can we live elsewhere in the universe?

It's a different story altogether if you want to live on another planet or the moon of another planet (including our own moon). To understand why, consider all of the enormous challenges facing humans who venture beyond Earth's warm embrace. First, there's the issue of getting there, which is really an issue of distance and time. A trip to our moon -- about 238,607 miles (384,000 kilometers) on average -- takes about three days, which seems perfectly reasonable. But move the landing site to Mars, and the travel time increases to about seven months. Move the landing site even farther, to Saturn's moon Titan, and the trip will take longer than three years.

These distances don't sound insurmountable until you realize how many supplies the spacecraft will have to carry to sustain the crew. For example, the vessel required to get a crew to Mars would need to be three to six times more massive than the lunar lander [source Zubrin]. Using current technology and given the unique conditions of the Martian atmosphere, such a craft would be impossible to land. Now imagine the size of a Saturn-bound rocket, packed to the rafters with food, water and other resources.

Mission planners also worry about the the social effects of a long journey into space. No one is quite sure how humans cooped up in a spacecraft for months or years at a time will respond, although Russian scientists are running experiments here on Earth to find out. In May 2010, the Russian Institute of Biomedical Problems sealed a six-man, multinational crew inside a simulated space vessel for 520 days to see how their mental and physical health fares in the close quarters. Other scientists think a same-sex crew, or a highly trained crew of any sort, is the wrong idea. An anthropologist at the University of Florida has proposed that large family groups would be better suited to making long voyages into deep space. In his plan, a starting population of 150 to 180 people, mostly childless married couples, would sustain itself over six to eight generations, enabling the group to reach planets far beyond our solar system [source: Keen].

Even if the social issues are solved, other challenges await humans who travel in space. One of the biggest is the constant stream of cosmic rays zipping through the galaxy. Cosmic rays are fast-moving elementary particles -- protons, electrons and stripped-down atomic nuclei -- that may originate from quasars, black holes or other objects in the universe. When these particles, encounter a human, they pass cleanly through, knocking holes in DNA as they go. Luckily for most humans, Earth's atmosphere protects us from cosmic rays. But crews traveling in outer space, even to Mars, would be exposed to dangerous doses of these high-velocity particles. They would develop cancers at higher rates and would suffer from cataracts, brain damage and other medical conditions caused by radiation poisoning [source: Parker].

The threat of cosmic rays doesn't end once a crew touches down on a foreign world. Consider the conditions on the two most likely candidates for colonization. The moon has no atmosphere, while Mars has a thin atmosphere. Neither destination would shield settlers from incoming radiation, so their living chambers would need to be buried beneath tons of soil. Even if scientists devise ways to protect colonists from cosmic rays, they will have to fulfill their basic needs. Building a self-sufficient colony that provides air, water, food, power and food will push current technologies to the limit and may require newer, more advanced technologies.

So, can we live elsewhere in the universe? If you define "elsewhere" as the moon or Mars, then yes, we can live elsewhere in the universe -- with a fairly significant investment of cash and innovation. If you define "elsewhere" as one of the exoplanets discovered by NASA's Kepler telescope, then the odds aren't in our favor. Such worlds may be reachable only in the realm of science fiction.

Keep reading for more links that travel to out-of-this-world places.