NASA astronaut Scott Kelly recently returned to Earth after living in space for 340 days.

While the opportunity to live in space for that long is a privilege reserved for a special few, this honor comes with a cost.

In space, astronauts are exposed to cosmic radiation that would otherwise be absorbed or deflected by Earth's protective atmosphere.

In fact, experts estimated for Scientific American, that astronauts are exposed 24 times more radiation per year than the average human is on Earth.

According to the World Nuclear Association there's no evidence to suggest anything below 100 millisieverts per year poses a significant risk to human health. However, space radiation particles carry more energy than most radioactive sources on Earth, and could have more harmful affects on the human body.

Therefore, radiation exposure is a major concern for astronaut health as NASA embarks on longer, deep-space missions to Mars and beyond. For an idea of what types of radiation you're exposed to on a daily basis, check out this chart: