Lightning storms on Saturn and Jupiter could create carbon soot that might be compressed into diamonds as it falls through the atmosphere.
Scientists theorise that lightning zaps molecules of methane in the upper atmospheres of Saturn and Jupiter, liberating carbon atoms. These atoms then stick onto each other, forming larger particles of carbon soot (which the Cassini spacecraft may have spotted in dark storm clouds on Saturn). As the soot particles slowly float down through ever-denser layers of gaseous and liquid hydrogen towards the planets’ rocky cores, they experience ever greater pressures and temperatures. The soot is compressed into graphite, and then into solid diamonds before reaching a temperature of about 8,000 °C, when the diamond melts, forming liquid diamond raindrops.
Inside Saturn, the conditions are right for diamond ‘hail’ to form, beginning at a depth of about 6,000 kilometres into the atmosphere and extending for another 30,000 km below that. If you had a robot there, it would sit there and collect diamonds raining down. Learn more here.