Astronauts sent to colonize Mars would be well advised to avoid getting pregnant en route to the Red Planet, according to a review of radiation hazards by three scientists.

High-energy particles bombarding the ship would almost certainly sterilize any female fetus conceived in deep space, making it that much more difficult to establish a successful Mars colony once the crew lands.

"The present shielding capabilities would probably preclude having a pregnancy transited to Mars," said radiation biophysicist Tore Straume of NASA Ames Research Center, lead author of the review published in the Journal of Cosmology.

Sex in space is a touchy subject for NASA, whose code of conduct for astronauts dictates that "relationships of trust" and "professional standards" are to be maintained at all times. But the logical outgrowth of human space exploration is colonization, write Straume and his co-workers, with Mars being our closest, best bet – and that would entail reproduction.

The DNA that guides development of a fertilized embryo and the functioning of all the cells in the body is easily damaged by the kind of radiation that would bombard astronauts on a Mars voyage and ultimately on the planet itself.