Here in the solar system we have a very interesting variety of planets, but they are limited by the composition of our Sun. Because planets, moons, asteroids, and other bodies are made of what is left after the Sun has completed its formation, their chemistry is thought to be related to our host.
But not all stars are made of the same things as our Sun, which means that there, in the vast expanses of our galaxy, we can expect to find exoplanets wildly different from the supply in our small solar system.
For example, stars that are rich in carbon compared to our Sun – with more carbon than oxygen – may have exoplanets that are made mostly of diamond, with little silica, if the conditions are right. And now in a laboratory, scientists have crushed and heated silicon carbide to find out what these conditions might be.
“These exoplanets look like nothing in our solar system,”
The idea that stars with a higher carbon-oxygen ratio than the Sun could produce diamond planets first emerged with the discovery of 55 Cancri e, a super-terrestrial exoplanet orbiting a star thought to be rich in carbon. 41 light years.
It was later discovered that this star was not as rich in carbon as previously thought, which turned to this idea – at least as far as 55 Cancri e is concerned.
But between 12 and 17 percent of planetary systems can be located around carbon-rich stars – and with thousands of stars hosting exoplanets identified to date, the diamond planet looks like a different option.
Scientists have already studied and confirmed the idea that such planets are probably composed mainly of carbides, carbon compounds and other elements. If such a planet is rich in silicon carbide, researchers suggest, and if there is water to oxidize silicon carbide and convert it to silicon and carbon, then with enough heat and pressure, carbon can become a diamond.
To confirm their hypothesis, they turned to a diamond anvil, a device used to squeeze small samples of material to very high pressure.
They took small samples of silicon carbide and immersed them in water. The samples were then placed in a diamond anvil cage that pressed them to a pressure of up to 50 gigapascals – about half a million times the Earth’s atmospheric pressure at sea level. After the samples were drained, the team heated them with lasers.
In total, they conducted 18 cycles of the experiment – and found that just as they had predicted, at high temperature and high pressure, their silicon carbide samples reacted with water to turn into silica and diamond.
Thus, the researchers concluded that at temperatures up to 2500 kelvins and pressures up to 50 gigapascals, in the presence of water, the planets of silicon carbide can be oxidized and their internal compositions can be dominated by silica and diamond.
If we could identify these planets — perhaps through their density profiles and the composition of their stars — then we could exclude them as life-accepting planets.
Their interior, researchers say, would be too difficult for geological activity and their composition would make their atmosphere inhospitable to life as we know it.
“This is an additional step that helps us understand and characterize our ever-increasing and improving observations of exoplanets,” said Alan-Suther.
“The more we learn, the better we will be able to interpret new data from upcoming future missions such as the James Webb Space Telescope and the Nancy Grace Space Telescope to understand the afterlife in our own solar system.”
The study was published in Journal of Planetary Science.