The planet around the star HD 209458 is somewhat special. It is being eaten away bit by bit, its atmosphere stripped off by the searing heat of its nearby star. The planet, HD 209458b, swings around its star in under four days, at a distance of only 7 million kilometres – a fraction of the comparative gulf that separates the Sun from Mercury. There, the planet is rapidly being roasted, its atmosphere blasted away like the tail of a comet, 10,000 tons of it every second.