But not all stars are made out of the same stuff as our sun, meaning that in the wider expanse of our galaxy, we can expect to find exoplanets different from what is offered in our small solar system.
For example, stars that are richer in carbon than our sun – with more carbon than oxygen – can have exoplanets that are primarily made of diamonds, with a little bit of silica, if the situation is fine. And now, in a laboratory, scientists squeezed and heated silicon carbide to find out what those conditions might be.
“These exoplanets are unlike anything in our solar system,” said geophysicist Harrison Allen-Sutter of Arizona State University’s School of Earth and Space Exploration.
The idea that stars with higher carbon-to-oxygen ratios than the Sun could produce the first diamond planet to emerge with the discovery of the first 55 Canary E, a super-Earth exoplanet orbiting star carbon rich in 41 light-years is believed.
It was later discovered that this star was not the same as previously thought carbon, which paid off that idea – at least as far as the 55 Canary E is concerned.
But between 12 and 17 percent of planetary systems can be located around carbon-rich stars – and diamond planets identified to date with thousands of exoplanet-hosting stars are a distinct possibility.
Scientists have already discovered this idea and confirmed that such planets are composed mainly of compounds of carbides, carbon and other elements. If such a planet was enriched with silicon carbide, the researchers hypothesized, and if water existed to oxidize silicon carbide and convert it to silicon and carbon, with enough heat and pressure, carbon could become a diamond .
To confirm his hypothesis, he turned to a diamond anvil cell, a device used to squeeze small samples of material to very high pressures.
They took minute samples of silicon carbide and immersed them in water. Then, the diamonds were placed in an anvil cell, which pressurized them to 50 gigapascals – nearly half a million times Earth’s atmospheric pressure at sea level. After squeezing the samples, the team heated them with lasers.
In all, he scored 18 of the experiment – and he found that, as he predicted, under high heat and high pressure, his silicon carbide samples reacted with water to convert to silica and diamond.
Thus, the researchers concluded that at temperatures up to 2,500 Kelvin, and pressures up to 50 gigapascals in the presence of water, silicon carbide planets may oxidize, and their internal compositions may be dominated by silica and diamonds.
If we can identify these planets – perhaps from their density profiles, and the composition of their stars – then we can rule them out as planets that can host life.
Their interiors, the researchers said, would be very difficult for geological activity, and their creation would make their atmosphere inhuman to life as we know it.
“This is an additional step to help us understand and characterize our ever-increasing and improved observations of exoplanets,” Allen-Sutter said.
“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 Roman Space Telescope so that the world can be understood beyond our solar system.”
The research has been published in The Planetary Science Journal.