Forget diamonds in the sky — it may actually be raining diamonds on Saturn and Jupiter, according to two planetary scientists.

Researchers have long wondered whether the high pressures inside the giant planets could turn carbon into diamond, and even though some researchers dispute their claim, Mona Delitsky of California Specialty Engineering in Flintridge, and Kevin Baines of the University of Wisconsin-Madison, now say it is possible. They are laying out their argument this week at a meeting of the American Astronomical Society's Division for Planetary Sciences in Denver, Colorado.

In their scenario, 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, they say.