Diamonds in Exoplanetary Skies? New Insights on Photochemical Hazes of Exoplanetary Atmospheres
It has been suggested that “haze,” a substance produced by atmospheric photochemistry, is ubiquitously present in the atmospheres of extrasolar planets (hereafter exoplanets). Haze is also found in the atmospheres of Saturn’s moon Titan and Pluto, and understanding the processes involved in its formation is crucial for studying atmospheric chemistry and planetary climate. Conventionally, haze in exoplanet atmospheres has been thought to consist of “black” soot-like material because of high temperature environment of exoplanets. However, recent atmospheric observations using the James Webb Space Telescope (JWST) have indicated that haze in several exoplanets may be composed of “white” materials, challenging previous assumptions.
Kazumasa Ohno, Project Assistant Professor of the National Astronomical Observatory of Japan, developed a new theoretical model for haze formation, incorporating the evolution of haze material composition, to investigate what substances constitute exoplanetary haze. The results showed that the previously expected soot-like material barely form in exoplanet atmospheres. Instead, the model suggested that diamonds—a previously unanticipated substance—could form in exoplanetary atmosphere. This outcome is attributed to the high-temperature, hydrogen-rich environments of exoplanetary atmospheres, which closely resemble the chemical vapor deposition (CVD) environments commonly used for synthesizing diamonds under low pressure in engineering applications. Future research can test the proposed hypothesis of whether diamond synthesis indeed occurs through observations of exoplanetary atmospheres as well as laboratory experiments that mimics exoplanetary environments, which will help to unveil the true nature of exoplanetary haze.
This research was published as “Photochemical Hazes in Exoplanetary Skies with Diamonds: Microphysical Modeling of Haze Composition Evolution via Chemical Vapor Deposition” in The Astrophysical Journal, dated December 12, 2024.
