Scattered through the solar system are billions of leftover scraps from its birth — rocky asteroids and icy comets that never got swept up into a planet. This episode explores what they are, why comets grow glowing tails, and how a stray one wiped out the dinosaurs.

You'll come away understanding the difference between an asteroid and a comet, where each comes from, why a comet's tail always points away from the Sun, and how humanity has begun to defend itself against an impact.

Talking Science is sponsored by Kinsoft. Visit www.kinsoft.com.au

Further reading: NASA – "Asteroids" and "Comets" overview pages; NASA/APL – "DART mission"; ESA – "Rosetta".