ET:

On Jupiter and Saturn, half-inch diamonds fall from the atmosphere like rain. ...New research by a NASA scientist says that up to 1,000 tonnes (2.2 million pounds) of diamonds are created in Saturn’s atmosphere every year, with Jupiter’s atmosphere being a prodigious producer of diamonds as well.

How it happens:

Diamond rain on Jupiter and Saturn begins in the upper atmosphere. Lightning strikes methane, turning it into soot (carbon). As the soot falls, pressure increases, and it turns into graphite. After falling for another 4,000 miles or so, the pressure is so great that the graphite turns into diamond.

Saturn not only has diamonds in the sky, it also has a massive rose over its north pole...