The Universe may be filled with exoplanets made of diamonds

A new study suggests that, given the right circumstances, this scenario would be possible in carbon-rich planets.

Exoplanets made of diamonds and silica may be common across the Universe, according to a new study published last month in The Planetary Science Journal.

The study, conducted by scientists from Arizona State University and the University of Chicago, suggests that, given the right circumstances, this scenario would be possible in carbon-rich planets.

An artist's impression of a planet rich in diamonds. Inside, the most prevalent minerals would be diamond and silica (layer with crystals in the illustration). The core (dark blue) could be an iron-carbon alloy. — An artist’s impression of a planet rich in diamonds. Inside, the most prevalent minerals would be diamond and silica (layer with crystals in the illustration). The core (dark blue) could be an iron-carbon alloy. (Credit: Shim / ASU / Vecteezy).

Carbon-to-oxygen ratio

Stars and planets in a system are formed from the same gas cloud, so their compositions are similar, but the proportion of the chemical elements can vary.

A star with a lower carbon-to-oxygen ratio, for example, will have planets like Earth, composed of silicates and oxides with a very low amount of diamond – here, the diamond content is about 0.001%.

However, when stars have a higher carbon-to-oxygen ratio, the planets in the system are more likely to be carbon-rich.

With that in mind, scientists hypothesized that if there were water at the time of their formation, these planets would be rich in diamonds.

Methodology

To test this hypothesis, scientists had to mimic the interior of carbide exoplanets, emulating conditions of high heat and high pressure.

To do this, they immersed silicon carbide in water and compressed the sample using diamond anvils. Then, they heated the material with lasers.

An unaltered carbon planet (left) transforms from a mantle dominated by silicon carbide to a mantle dominated by silica and diamond (right). The reaction also produces methane and hydrogen. (Credit: Harrison / ASU).

To monitor the procedure, the researchers performed X-ray measurements while the laser heated the pressurized samples.

The result, as they report, was as expected: silicon carbide reacted with water and turned into diamonds and silica.

Habitability and inhabitability

Astrophysicists explain that, if they do exist, these exoplanets are unlikely to be habitable, since it is very rare for carbon-rich planets to be geologically active.

To retain an atmosphere, a planet needs a magnetic field. And to have a magnetic field, it needs to be geologically active. So, carbon-rich planets are unlikely to have an atmosphere.

“Regardless of habitability, this is one additional step in helping us understand and characterize our ever-increasing and improving observations of exoplanets,” said lead author Harrison Allen-Sutter of ASU’s School of Earth and Space Exploration.