Carbon-Rich Exoplanets May Be Made of Diamonds

As missions like NASA’s Hubble Space Telescope, TESS, and Kepler continue to provide insights into the properties of exoplanets (planets around other stars), scientists are increasingly able to piece together what these planets look like, what they are made of, and if they could be habitable or even inhabited. In a new study published recently in The Planetary Science Journal, a team of researchers from Arizona State University and the University of Chicago has determined that some carbon-rich exoplanets, given the right circumstances, could be made of diamonds and silica.

Lead author Harrison Allen-Sutter of ASU’s School of Earth and Space Exploration said:

Subscribe to our Newsletter!

Receive selected content straight into your inbox.

“These exoplanets are unlike anything in our solar system.”

Diamond formation in exoplanets

When stars and planets are formed, they do so from the same cloud of gas, so their bulk compositions are similar. A star with a lower carbon-to-oxygen ratio will have planets like Earth, comprised of silicates and oxides with a very small diamond content (Earth’s diamond content is about 0.001 percent).

Some carbon-rich exoplanets have diamond and silica as the main minerals. Water can convert a carbide planet into a diamond-rich planet.
Some carbon-rich exoplanets have diamond and silica as the main minerals. Water can convert a carbide planet into a diamond-rich planet. In the interior, the main minerals would be diamond and silica (a layer with crystals in the illustration). The core (dark blue) might be iron-carbon alloy. (Image: Shim via ASU / Vecteezy)

But exoplanets around stars with a higher carbon-to-oxygen ratio than our Sun are more likely to be carbon-rich. Allen-Sutter and co-authors Emily Garhart, Kurt Leinenweber, and Dan Shim of ASU, with Vitali Prakapenka and Eran Greenberg of the University of Chicago, hypothesized that these carbon-rich exoplanets could convert to diamond and silicate if water (which is abundant in the universe) were present, creating a diamond-rich composition.

Diamond-anvils and X-rays

To test this hypothesis, the research team needed to mimic the interior of carbide exoplanets using high heat and high pressure. To do so, they used high-pressure diamond-anvil cells at co-author Shim’s Lab for Earth and Planetary Materials. First, they immersed silicon carbide in water and compressed the sample between diamonds to a very high pressure.

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

Then, to monitor the reaction between silicon carbide and water, they conducted laser heating at the Argonne National Laboratory in Illinois, taking X-ray measurements while the laser heated the sample at high pressures. As they predicted, with high heat and pressure, the silicon carbide reacted with water and turned into diamonds and silica.

Habitability and uninhabitability

So far, we have not found life on other planets, but the search continues. Planetary scientists and astrobiologists are using sophisticated instruments in space and on Earth to find planets with the right properties and the right location around their stars where life could exist. For carbon-rich planets that are the focus of this study, however, they likely do not have the properties needed for life.

The cylinder-shaped objects in this photo are diamond anvil cells. The diamond-anvil cells are mounted in copper holders and then inserted into the synchrotron X-ray/laser beam path. The photo shows diamond-anvil cells and mounts before they are aligned for X-ray/laser experiments.
The cylinder-shaped objects in this photo are diamond anvil cells. The diamond-anvil cells are mounted in copper holders and then inserted into the synchrotron X-ray/laser beam path. The photo shows diamond-anvil cells and mounts before they are aligned for X-ray/laser experiments. (Image: Shim via ASU)

While Earth is geologically active (an indicator of habitability), the results of this study show that carbon-rich planets are too hard to be geologically active and this lack of geologic activity may make atmospheric composition uninhabitable. Atmospheres are critical for life as it provides us with air to breathe, protection from the harsh environment of space, and even pressure to allow for liquid water. Allen-Sutter said:

“Regardless of habitability, this is one additional step in helping us understand and characterize our ever-increasing and improving observations of exoplanets. The more we learn, the better we’ll be able to interpret new data from upcoming future missions like the James Webb Space Telescope and the Nancy Grace Roman Space Telescope to understand the worlds beyond our own solar system.”

Provided by: Karin Valentine, Arizona State University [Note: Materials may be edited for content and length.]

Follow us on TwitterFacebook, or Pinterest

Recommended Stories

A Chinese paddlefish.

One of the World’s Oldest and Largest Fish Is Now Extinct

Chinese paddlefish, which reached up to 23 feet in length, have become extinct according to ...

Trees growing in a shallow lake.

A Very Rare Turtle Just Died, Pushing the Species Close to Extinction

On April 12, a female Yangtze giant softshell turtle died in the Suzhou Shangfangshan Forest ...

A slider turtle.

Chinese Flight Crew Arrested for Smuggling Endangered Turtles

On June 21, two China Eastern Airlines crew members were arrested at Los Angeles International ...

A Uyghur father and son sharing with a friend.

Chinese Government Now Forcing Uyghurs to Use Sinicized Furniture

In what seems like a bizarre demand, the Chinese regime is now asking the Uyghur ...

Three Uyghur children.

Over Half a Million Uyghur Children Separated From Their Parents

Beijing’s persecution of Uyghurs is not only affecting adults but also Uyghur children, according to ...

The European Parliament.

Condemnation of the Uyghur Persecution and the 2022 Winter Olympics

Taking into account the Chinese regime’s brutal treatment of the Uyghur ethnic minority in Xinjiang, ...

Documents from China Cables.

Even Overseas, China Keeping Close Track on Uyghurs

A set of classified Chinese documents released by the International Consortium of Investigative Journalists (ICIJ) ...

Kepler witnesses vampire star system undergoing super-outburst

Kepler Witnesses Vampire Star System Undergoing Super-Outburst

NASA’s Kepler spacecraft was designed to find exoplanets by looking for stars that dim as ...

Chinese wearing masks.

How Is the Coronavirus Spreading Across the Globe?

The first case of a novel strain of coronavirus has been confirmed in the United ...

Send this to a friend