It is known that human, animal and plant physiology has been shaped by gravity.  What are the potential risks for human beings of prolonged stay in outer space or on other planets or bodies with different gravity fields such as the Moon or Mars?  If human colonies were to be on extraterrestrial bodies for long periods of time, how could their physiologies conceivably develop or differ from staying on Earth?  Finally, what do we know about how animals and plants develop in extraterrestrial environments?

This is a complex question, and there is a large relevant scientific literature under the heading of “gravitational biology”.  Two good resources are the American Society for Gravitational and Space Biology ( and the Life Science Division at NASA Ames Research Center (  Humans have been exposed for more than a year in space (microgravity), and almost all have experienced loss of bone and muscle mass and some small changes in blood volume and chemistry.  This sort of adaptation in microgravity is no problem in space (some people even think that space is a healthier environment than the surface of the Earth), but considerable re-adaptaion is required when the astronauts or cosmonauts return to Earth.  An environment with low but not zero gravity (such as Moon or Mars) is probably not as severe as microgravity, and it seems probable that people could live on those worlds for long periods of time.  If they exercised hard to maintain their conditioning, they might even return to Earth with minimal risk.  But we have not yet studied the effects of partial gravity on people or even on plants and mammals, so we don’t know.  The large centrifuge built by NASA and the Japanese Space Agency for the Space Station would have allowed scientific tests to be made, but this component of the Space Station was canceled last year and will thus probably never be launched.

David Morrison

NLSI Interim Director

May 7, 2007

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The Apollo missions brought back 842 pounds of lunar samples to analyze in labs on Earth.

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