Carbon-rich exoplanets may consist of diamonds and silica

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As space exploration missions provide more and more detailed information about the properties of exoplanets (planets around other stars), scientists are increasingly able to summarize these data. In this way, they will learn what these distant planets look like, what they consist of and whether they can even be inhabited.

In a new study recently published in The Planetary Science Journal, a team of scientists from the University of Arizona (ASU) and the University of Chicago found that some carbon-rich exoplanets may well be composed of diamonds and silica under certain conditions.

When stars and planets originate, they take their composition from the same gas cloud, so it is generally similar everywhere. However, a star with a lower carbon to oxygen ratio will have planets similar to the Earth, i.e. consisting of silicates and oxides with very little diamond content (in particular, the diamond content on Earth is only 0.001%). But exoplanets around such stars, where the ratio of carbon to oxygen is higher than our Sun, are more likely to be very rich in carbon. Scientists have hypothesized that exoplanets of this kind can eventually turn into diamonds and silicates through the medium of water (which is a lot of water in the universe), in fact creating an amazing diamond rich composition.

To test this version, the research team had to simulate the inside of carbide exoplanets under high temperature and pressure. To do this, they took cells with high pressure diamond anvils. First, they submerged the silicon carbide in water and clamped the sample between the diamonds until a very high pressure was reached. Then, in order to track the reaction between the silicon carbide and the water, they carried out laser heating while taking X-ray measurements. As they expected, at high temperature and pressure, silicon carbide reacted with water and turned into diamonds and silica.

So far, life on other planets has not been detected, but the search continues. Planetary scientists and astrobiologists use sophisticated tools in space and on Earth to find planets with the right properties and the right location around their stars, where life could exist.

However, for the carbon-rich planets that are the subject of this study, it is fair to say that they probably do not have the properties necessary for life.

Although the Earth is geologically active (and this is one of the indicators of habitability), the results of this study show that planets rich in carbon are too difficult to be geologically active and this can make the composition of the atmosphere uninhabitable. The atmosphere is critical to life because it provides air for breathing, protection from the harsh conditions of space, and even pressure to let water through in liquid form.