Diamonds in Space
'Diamond rain' falls on Saturn and Jupiter BBC - October 14, 2013
Diamonds that are the right size to have been worn by stars of the Silver Screen could rain 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, they say. 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 centimeter in diameter - "big enough to put on a ring, although of course they would be uncut," says Dr. Kevin Baines, of the University of Wisconsin-Madison and NASA's Jet Propulsion Laboratory. He added they would be of a size that the late film actress Elizabeth Taylor would have been "proud to wear". "The bottom line is that 1,000 tons of diamonds a year are being created on Saturn. "People ask me - how can you really tell? Because there's no way you can go and observe it. It all boils down to the chemistry. And we think we're pretty certain."
Uranus and Neptune have long been thought to harbor gemstones. But Saturn and Jupiter were not thought to have suitable atmospheres. Researched analyzed the latest temperature and pressure predictions for the planets' interiors, as well as new data on how carbon behaves in different conditions.
They concluded that stable crystals of diamond will hail down over a huge region of Saturn in particular. It all begins in the upper atmosphere, in the thunderstorm alleys, where lightning turns methane into soot. As the soot falls, the pressure on it increases. And after about 1,000 miles it turns to graphite - the sheet-like form of carbon you find in pencils."
By a depth of 6,000km, these chunks of falling graphite toughen into diamonds - strong and unreactive. These continue to fall for another 30,000km - about two-and-a-half Earth-spans. Once you get down to those extreme depths, the pressure and temperature is so hellish, there's no way the diamonds could remain solid. One possibility is that a "sea" of liquid carbon could form.
Diamonds aren't forever on Saturn and Jupiter. But they are on Uranus and Neptune, which are colder at their cores. The findings are yet to be peer reviewed, but other planetary experts contacted by BBC News said the possibility of diamond rain "cannot be dismissed". The idea that there is a depth range within the atmospheres of Jupiter and (even more so) Saturn within which carbon would be stable as diamond does seem sensible," says Prof Raymond Jeanloz, one of the team who first predicted diamonds on Uranus and Neptune. And given the large sizes of these planets, the amount of carbon (therefore diamond) that may be present is hardly negligible.
Further work was needed to understand whether carbon can form diamonds in an atmosphere which is rich in hydrogen and helium - such as Saturn's. The planet 55 Cancri-e may not be so precious after all, a new study suggests.