Outer space is an extremely hostile place. If you were to step outside a spacecraft, such as the International Space Station, or on a world with little or no atmosphere such as the moon or Mars without the protection of a space suit, then the following things would happen:
  • You would lose consciousness because there is no oxygen. This could occur in as little as 15 seconds.
  • Because there is no air pressure to keep your blood and body fluids in a liquid state, the fluids would "boil." Because the "boiling process" would cause them to lose heat energy rapidly, the fluids would freeze before they were evaporated totally (There is a cool display in San Francisco's science museum, The Exploratorium, that demonstrates this principle!). This process could take from 30 seconds to 1 minute. So, it was possible for astronaut David Bowman in "2001: A Space Odyssey" to survive when he ejected from the space pod into the airlock without a space helmet and repressurized the airlock within 30 seconds.
  • Your tissues (skin, heart, other internal organs) would expand because of the boiling fluids. However, they would not "explode" as depicted in some science fiction movies, such as "Total Recall."
  • You would face extreme changes in temperature
    • sunlight - 248 degrees Fahrenheit or 120 degrees Celsius
    • shade - minus 148 degrees Fahrenheit or minus 100 degrees Celsius
  • You would be exposed to various types of radiation (cosmic rays) or charged particles emitted from the sun (solar wind).
  • You could be hit by small particles of dust or rock that move at high speeds (micrometeoroids) or orbiting debris from satellites or spacecraft.
You would die quickly because of the first three things listed, probably in less than one minute. The movie "Mission to Mars" has a scene that realistically demonstrates what would happen if an astronaut's space suit were to rapidly lose pressure and be exposed to outer space. So to protect astronauts, NASA has developed elaborate space suits.

Here are some interesting links: