Exoplanets rich in carbon could be made up of diamonds and silica, say researchers

The latest space missions like NASA's Hubble Space Telescope, TESS and Kepler have helped astronomers in getting interesting insights about the properties of exoplanets (planets around other stars), allowing them to identify what these planets look like, what they are made of, and if they could be habitable.

According to a new study published in The Planetary Science Journal, a team of researchers from Arizona State University (ASU) and the University of Chicago have ascertained that some exoplanets that are rich in carbon, could be made of diamonds and silica in favourable circumstances.

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How are diamond exoplanets formed?

Stars and planets are formed from the same cloud of gas, so the majority of their compositions are similar. A star with a lower carbon to oxygen ratio will have planets like Earth, comprised mainly of silicates and oxides with a very small 0.001% diamond content.

But exoplanets near stars with a higher carbon to oxygen ratio compared to our Sun are generally rich in carbon. The researchers have hypothesized that these carbon-rich exoplanets could convert to diamond and silicate, in the presence of water (which is abundant in the universe), creating a diamond-rich composition.

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Experiment using Diamond-anvils

To test this hypothesis, the research team needed to mimic the interior of carbide exoplanets using high heat and high-pressure diamond-anvil cells.

First, they immersed silicon carbide in water and compressed it between diamonds to very high pressure. To monitor the reaction between silicon carbide and water, they conducted laser heating and noted X-ray measurements while the laser-heated the sample at high pressures. As predicted, the silicon carbide reacted with water under high heat and pressure, turning into diamonds and silica.

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Habitability and inhabitability of diamond exoplanets

Planetary scientists and astrobiologists have been using sophisticated instruments in space and on Earth to locate planets around stars with the right properties for the existence of life. However, carbon-rich planets that are the focus of this study, do not have the properties for habitability.

While Earth is geologically active, the result of this study shows that carbon-rich planets are so hard to be geologically active that it may make atmospheric composition uninhabitable. Atmospheres are critical for life as it provides us with air to breathe, protects us from the harsh environment of the space, and even pressure to allow the flow of liquid water.

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(Photo for representation, Credits: Getty Images)