Sorry, Stephen Hawking. The astrophysicist's grandiose plan for the human race to leave Earth and colonize the far reaches of space may never come to fruition. Why? Because NASA has discovered that space is "simply not a good place to have sex." Here, a quick guide to our outer-space fertility problem:

Why couldn't humans colonize space?
Because any child conceived and born in space is likely to be born sterile. Scientists at NASA say that the high levels of radiation in space would kill any female fetus' lifetime supply of eggs, while males in the womb would likely become sterile. The child could also suffer "mental and physical defects" from exposure to harmful radiation.

Couldn't spaceships protect against this kind of radiation?
No. These are no ordinary protons, but high-energy proton particles from galactic cosmic rays. We on Earth are kept safe from them by our atmosphere and magnetic field, but astronauts in space remain vulnerable.

Has anyone had sex in space before?
It's not clear, says Jason Mick at Daily Tech. Both NASA and the Russians refuse to reveal if their astronauts had ever attempted "zero-G docking maneuvers" in space. The only couple to have traveled together into space — husband and wife team Jan Davis and Mark Lee — remain tight-lipped about whether or not they "got their stellar groove on."

Would the same issue affect colonists on Mars?
No, says James Walker at Gearfuse. The atmosphere of Mars would likely give some protection against these rays. All of which suggests that the problem is "more of an issue for colonization outside of the solar system." Just so long as the astronauts "practice self-restraint while hurtling toward the Red Planet," the human race might be able to procreate away from Earth after all.

Sources: The Independent, Gearfuse, Daily Tech