Through the development of a novel model to estimate exoplanet composition, Yale astronomers have found that carbon-rich planets, some of which could possess huge quantities of graphite or diamonds, may be more abundant than once thought. The study has been published in the Astrophysical Journal.
As planets grow the gaseous pool, or disk, in which they form changes; it is this chemical evolution that is largely responsible for the composition of the planet. Astronomers are particularly interested in exoplanet (planets outside of our solar system) carbon composition because this has implications on geological processes such as plate tectonics, but perhaps more importantly for life.
“Despite the relatively small amount of carbon on Earth, carbon has been critical for the emergence of life and the regulation of our climate through the carbon-silicate cycle,” said lead researcher John Moriarty in a news-release. “It’s an open question as to how carbon-rich chemistry will affect the habitability of exoplanets. We hope our findings will spark interest in research to help answer these questions.”
Some of the main elements that Earth is comprised of are iron, oxygen, magnesium and silicon; carbon on the other hand only makes up around 0.005% of the total. It’s thought that rocky exoplanets generally possess a similar composition, whereas carbon-rich planets could contain up to three-quarters of their total mass in carbon.
Previously, in order to predict the composition of these planets astronomers based models on the chemical composition of the planetary disks at a single moment in time. The model developed for this study, however, follows the disk as it changes over time.
The researchers presented two key findings in their report. First, it was discovered that carbon-rich planets with disks containing carbon-oxygen ratios greater than 0.8 can form farther out from the disk centre than predicted. Second, they found that if planet formation occurs in close proximity to a host star, carbon-rich planets can form within disks containing carbon-oxygen ratios as low as 0.65, which is in contrast to previous predictions that suggested ratios of at least 0.8 are required.
According to Debra Fisher, one of the authors of the study, the results highlight important questions which remain unanswered; in particular, whether Earth can be considered a typical rocky planet. “This work further expands the range of factors that may bear on the habitability of other worlds," she adds.