When it comes to sheer celestial bling, stars might not corner the market on twinkle. Because beneath their rocky exteriors, some terrestrial planets may be half diamond. So said scientists at the fall meeting of the American Geophysical Union. [Cayman T. Unterborn, Wendy R. Panero and Jason E. Kabbes, "Diamond, Carbide and Carbonate Planets"]

The researchers were fixing to study how diamonds form here on Earth, under the conditions found in the planet’s lower mantle. So they took a tiny sample of iron, carbon, and oxygen, elements abundant in Earth’s interior, and cooked it up at about 3,800 degrees Fahrenheit and 9.5 million pounds of pressure per square inch. What they saw was that iron hooks up with oxygen to produce rust, and leaves behind pockets of carbon, which become diamond.

Now, what happens if they look not at Earth but at a planet in a solar system where there’s even more carbon? According to the model, the carbon merges with iron to form a core made of steel, leaving a carbon mantle rich with diamond.

Whether the Milky Way harbors such gems is still an open question. One thing is for sure: they probably wouldn’t harbor life. Because diamonds readily transfer heat. So a planet made of diamond would be one cold stone.

—Karen Hopkin

[The above text is a transcript of this podcast.]