You're listening to Song Exploder, where musicians take apart their songs and piece by piece, tell the story of how they were made. I'm Rishikesh, your way.

I got to figure out a way for grow. Three years worth of food here. I'm on a planet where nothing grows. Luckily, I'm a botanist.

That's a clip from the film The Martian, where Matt Damon plays astronaut Mark Watney, who's stranded on Mars and has to rely on science and ingenuity in order to survive.

At the time of this recording, the film's been number one at the box office for two weeks straight.

In this episode, composer Harry Gregson Williams breaks down his music from the film, where part of his job was to score the excitement of scientific discovery and the grandeur and mystery of Mars itself.

He begins with how director Ridley Scott first offered in the job to work on the film.

A script plopped through the letterbox one day with a terse little note on it which said, read it, like it, do it.

I'd plowed through the script in one hungry sitting and it was in a brainer man. I certainly wanted to do something.

I'm Harry Gregson Williams and I'm the composer of the Martian score.

Our first conversations were about tone and color and he showed me a very, I thought, very complete first assembly of the film.

So the film had really taken shape by the time I came to it.

The outcome of the first meeting really was that I should focus on Watney, you know, Matt Damon's character, which is pretty clear that I should from the script.

His optimism for life, his love of science and problem solving that he always seems to be able to handle with humor and charisma.

All this should be reflected in the music. You know, there was no reason for the music to be too dark for too long in this film.

And that was quite a revelation to begin with because I had thought there would be a lot of darkness and despair.

He's only hanging on to a tiny thread of belief that he could live, but for the most part, this is a guy who's up for the challenge.

The piece of music that you picked out here has the technological, scientific aspect of him talking into a camera.

And no one else there, him alone on Mars, he looks like he's made up his mind. This is it. This is the day that he's going to leave.

The queue's going to start with bass fanats and low-chellion basses.

This little theme board comes a couple of times in the movie and it's quite austere. It's part of a Mars motif.

And then the moon changes somewhat. Brightens. We get to Watney, who's smiling.

We hear a little harp thing with a bit of delay on it, which gives us a little spring in our step.

...