Diamonds big enough to be worn are raining down on Saturn and Jupiter, US scientists have calculated. New atmospheric data for the gas giants indicates that carbon is abundant in its dazzling crystal form. Lightning storms turn methane into soot (carbon) which as it falls hardens into chunks of graphite and then diamond. These diamond "hail stones" eventually melt into a liquid sea in the planets' hot cores. The biggest diamonds would likely be about a centimetre in diameter. The bottom line is that 1,000 tonnes of diamonds a year are being created on Saturn.