Uranus has no diamonds after all

Hunting for diamonds on Uranus or Neptune would be a lost cause, say
the authors of a new study. Contrary to previous suggestions, these two
planets do not have enough carbon to make diamonds, they say – but
white dwarf stars do.

Some scientists have proposed that the high pressure inside Uranus and Neptune could compress carbon into diamonds.

But the authors say diamonds should be present inside white dwarf
stars, which are the dense cores left behind when stars like the Sun
use up all of their nuclear fuel and throw off their outer layers.

Some
of these white dwarfs are expected to contain about 50% carbon, which
would be more than enough to produce diamonds. When the white dwarf is
young and hot, the carbon would exist in the form of a liquid. "You
could almost say it's like liquid diamond," he says.