The James Webb Space Telescope (JWST) has achieved a groundbreaking discovery by detecting ultraviolet-fluorescent carbon monoxide in a protoplanetary debris disk for the first time. This finding, detailed in a preprint study led by Cicero Lu from the Gemini Observatory, offers new insights into the processes of planetary formation.
Located approximately 500 light years away in the Centaurus constellation, the star HD 131488 is about 15 million years old and classified as an “Early A-type” star, indicating it is hotter and more massive than our Sun. Previous observations, including those from the Atacama Large Millimeter/submillimeter Array (ALMA), had already identified significant amounts of cold carbon monoxide gas and dust in the outer regions of the disk, situated roughly 30-100 astronomical units (AU) from the star.
Unveiling the Inner Disk
Recent infrared data from both the NASA Infrared Telescope Facility and the Gemini Observatory hinted at the presence of hot dust and solid-state features in the inner zones of the disk. Optical studies suggested the existence of hot atomic gases, such as calcium and potassium, further enriching the understanding of this complex environment.
The JWST’s infrared capabilities allowed for a focused examination of HD 131488 in February 2023, revealing a small quantity of “warm” CO gas—approximately one-hundred-thousandth the mass of the cold gas found in the outer disk. This gas was distributed between 0.5 AU and 10 AU from the star, showcasing distinct properties that challenge existing theories.
A significant finding was the disparity between the vibrational and rotational temperatures of the CO molecules. The vibrational temperature reached a maximum of about 8,800K, while the rotational temperature peaked at around 450K. In typical gas environments, these temperatures align due to collisions that establish local thermal equilibrium. The stark contrast observed around HD 131488 indicates that these molecules are not in equilibrium, contributing to their fluorescent emissions.
Implications for Planetary Formation
The research also uncovered a high ratio of Carbon-12 to Carbon-13, suggesting that dust grains within the warm gas cloud may be obstructing light. For the observed fluorescent pattern to occur, the CO molecules require “collisional partners”—other molecules that interact with them and absorb energy. The study suggests that water vapor from disintegrating comets is a likely candidate, supporting the hypothesis that the gas is continuously replenished by cometary collisions.
Scientists have debated the origins of CO-rich debris disks like that of HD 131488. Two primary theories propose either that these disks are remnants from the star’s formation or that gases are sustained by ongoing cometary activity. The findings from this study lend strong support to the latter theory.
The presence of substantial carbon and oxygen within this “terrestrial zone” indicates that any planets forming in this environment would exhibit high metallicity, contrasting with hydrogen-rich primordial nebulae. This finding enriches the narrative of how rocky planets may develop in such systems.
The discoveries made by the JWST continue to demonstrate its capabilities and the potential for new revelations about planetary formation. As research progresses, it is likely that more star systems akin to HD 131488 will provide further evidence in the study of CO-rich disks, shedding light on the complex dynamics of planetary formation in the universe.
