“The search for planets is the search for life,” said Natalie Batalha, a Kepler mission scientist from NASA’s Ames Research Center. In the search for Earth-like habitable planets, occasionally something truly weird pops up, something unlike anything in our solar system.
The “Exoplanet Era” officially began in October 1995, when Nobel-Prize laureates Michel Mayor and Didier Queloz revealed the first discovery of a planet outside our solar system, an exoplanet, orbiting a solar-type star in our home galaxy, the Milky Way –planet 51 Pegasi b, a gaseous ball comparable with the solar system’s biggest gas giant, Jupiter. Their discovery started a revolution in astronomy and over 4,100 exoplanets have since been found in the Milky Way. And strange new worlds are being discovered almost daily.
One of those weird “somethings” was announced by a team of researchers from Arizona State University (ASU) and the University of Chicago with a new study published in The Planetary Science Journal. The team determined that some carbon-rich exoplanets, given the right circumstances, could be made of diamonds and silica. “These exoplanets are unlike anything in our solar system,” says lead author Harrison Allen-Sutter of ASU’s School of Earth and Space Exploration.
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%).
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 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.
Testing the Hypothesis
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. 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.
Some astronomers have said that it’s irrelevant whether or not there are other forms of life discovered in the Milky Way or in other galaxies. The fact that we are here provides an ‘existence proof’ as it is called in mathematics. But so far, 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. While Earth is geologically active (an indicator 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.
“Regardless of habitability, this is one additional step in helping us understand and characterize our ever- increasing and improving observations of exoplanets,” says Allen-Sutter. “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 on our own solar system.”
The Daily Galaxy, Sam Cabot, via Arizona State University
Image credit: Shutterstock License