Twinkle is a small, low-cost mission that will use spectroscopy to decode the light from hundreds of extrasolar planets. Twinkle will be able to reveal, for the first time, the chemical composition, weather and history of worlds orbiting distant stars. The Twinkle satellite will be built in the UK and launched into a low-Earth orbit within 3 to 4 years, using a platform designed by Surrey Satellite Technology Ltd and instrumentation led by UCL.