When Apollo 11 astronauts Buzz Aldrin and Neil Armstrong landed safely on the moon in July 1969, NASA and the entirety of the United States rejoiced knowing it was the first country to successfully put a man on the moon. Cameras rolled, flags were planted, and President Richard Nixon’s administration breathed a heavy sigh of relief because he would not have to read this poignant letter titled “In Event of Moon Disaster” that would have commemorated both astronauts’ sacrifice.

Dying in space is a grim reality that all astronauts must accept as a possibility. It’s also something we all consider while watching movies that take place outside the grip of Earth’s gravity. Would astronaut David Bowman really survive without his helmet in 2001: A Space Odyssey? Would space pirate Marc Watney really live through a puncture in his suit while stranded on Mars in The Martian? The grisly manner of death depicted in Total Recall is often regarded as the most famous and graphic portrayal of space exposure in Hollywood, but not exactly as the most authentic.

So how does the human body react to deep space exposure? Brit Lab’s Dara O Briain and Mark Miodownik discuss the so-called vacuum of space and how long someone would last out there without a spacesuit. Answer: not very long.

As Miodownik explains, exposure to space does not result in instant death, but it comes pretty close. A person would become extremely cold almost instantly. A sudden and significant drop in pressure would cause blood to boil, and as the vapor pressure goes down it results in extremely low temperatures. But don’t worry about freezing to death. You would be dead from asphyxiation within moments due to the whole lack of breathable air — and holding your breath would just lead to a pair of exploded lungs. For an up close and personal look at what would happen to your blood, click on the video to see Miodownik’s experiment.