As missions like NASA’s Hubble Space Telescope, TESS and Kepler continue to provide insights into the properties of exoplanets (planets around other stars), scientists are increasingly able to piece together what these planets look like, what they are made of, and if they could be habitable or even inhabited.
In a new study published recently in The Planetary Science Journal, a team of researchers from Arizona State University (ASU) and the University of Chicago have 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.
Diamond exoplanet formation
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 percent).
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 Emily Garhart, Kurt Leinenweber and Dan Shim of ASU, with Vitali Prakapenka and Eran Greenberg of the University of Chicago, 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.
Diamond-anvils and X-rays
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.
Habitability and inhabitability
So far, we have not found life on other planets, but 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.”
- 45A new international study led by astrophysicist Eric Agol from the University of Washington has measured the densities of the seven planets of the exoplanetary system TRAPPIST-1 with extreme precision, the values obtained indicating very similar compositions for all the planets. This fact makes the system even more remarkable and…
- 38A newly discovered planet could be our best chance yet of studying rocky planet atmospheres outside the solar system, a new international study involving UNSW Sydney shows. The planet, called Gliese 486b (pronounced Glee-seh), is a “super-Earth”: that is, a rocky planet bigger than Earth but smaller than ice giants…
- 38An atmosphere is what makes life on Earth's surface possible, regulating our climate and sheltering us from damaging cosmic rays. But although telescopes have counted a growing number of rocky planets, scientists had thought most of their atmospheres long lost. However, a new study by University of Chicago and Stanford…
- 37In the search for planets capable of sustaining life, an international research team with members from ETH has taken a significant step forward. As the researchers reported recently in the journal Nature Communications, they found signs of a Neptune-sized planet in the Alpha Centauri star system, a mere 4.4 light years…
- 31Australian scientists have developed a new type of sensor to measure and correct the distortion of starlight caused by viewing through the Earth's atmosphere, which should make it easier to study the possibility of life on distant planets. Using artificial intelligence and machine learning, University of Sydney optical scientists have…