When I was a child, I’d stare at the stars and think, “Even if it means I’ll never come back to Earth, I’ll do anything to get on a spaceship and travel to distant planets.”

I usually thought this the night before a physics test, when I would have done anything to board a spaceship and never attend science classes again. I hated physics; I never understood it.

Oh, the irony. It never occurred to me then that you can’t get to outer space without physics. And chemistry. And biology. You need science to create the technology that will blast humans out of Earth’s gravitational pull. And you need science to create the technology that will allow earthly creatures like humans to survive on planets that are not Earth.

Perhaps I would not have thought so cheerfully about zipping off to the stars and never coming back if I’d read Mary Roach’s Packing for Mars: The Curious Science of Life in the Void, a hilarious book about the real physics, chemistry and biology of the human body as it would function in space.

Mary Roach is a journalist and humour writer with an interest in science and in Packing for Mars, she travels all over the world to learn from scientists and astronauts what it would take to make a human feel at home on Mars.

Rocket scientists find the human body annoying. That’s because it was never made for other planets. It was made only for Earth, with its oxygen, a liquid called H2O, certain nutrients, and a particular level of gravitational pull. And for a human body to leave Earth, it needs a huge amount of technology to help it survive.

What kind of technology? Roach learns things we usually don’t think about when we dream of packing for another planet. For instance: pee and poo. On Earth, the concepts of up and down are fixed, because of gravity; when we sit on the pot, pee and poo go down.

But there’s no gravity in outer space. Without a technological solution, every astronaut would have to duck flying pee.

Roach also learns a lot about boredom to answer questions like: Can you bear being in a confined space, as you travel in space, with little to do until you land? And how good will you be, after days of doing the same boring tasks over and over, in an emergency?

And what happens when you’re on Mars anyway? Where will you get food? Where will you get water? (Hint: remember that flying pee?)

Moving to another planet is all about questions — just as many questions as there are suns, planets, asteroids and moons in the infinity of space. And before you wave a cheerful goodbye and blast off, science must find all the answers. In this not-very-long book, Mary Roach presents both questions and some answers.

If I’d read this book when I was a 14- or 15-year-old dreaming of my Great Science Escape, I wouldn’t have wanted to pack for Mars. I’d have rushed to school instead, ready to learn everything I could about physics.