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 When it comes to sheer celestial¹ bling, stars might not corner the market on twinkle, because beneath their rocky exteriors², some terrestrial planets may be half diamond. So said scientists at the fall meeting of the American Geophysical Union. 

 

The researchers were fixing to study how diamonds form here on Earth, under the conditions found in the planet’s lower mantle³. 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 Fahrenheit⁴ and 9.5 million pounds of pressure per square inch. What they saw was that iron hooks up with oxygen to produce rust⁵, 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 merges⁶ with iron to form a core made of steel, leaving a carbon mantle rich with diamond.

 

Whether the Milky⁷ Way harbors such gems⁸ 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.

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