More than 5,000 exoplanets have been identified orbiting stars beyond the Sun, many of which differ significantly from known Solar System planets. A prominent category of exoplanets falls between Earth and Neptune in size. These worlds have sparked debates among scientists, who question whether they are rocky super-Earths with thick hydrogen atmospheres or icy Neptune-like planets surrounded by water-rich atmospheres. Previous efforts to understand these planets were hindered by high-altitude clouds that obscured their underlying atmospheres.
An international research team, led by Everett Schlawin from the University of Arizona and Kazumasa Ohno of the National Astronomical Observatory of Japan, utilized JWST to study GJ 1214 b, a prime example of this enigmatic category of exoplanets. Located 48 light-years away in the constellation Ophiuchus, GJ 1214 b is among the easiest of its kind to observe.
New data revealed that GJ 1214 b's atmosphere is not hydrogen-rich or water-based. Instead, it contains concentrations of carbon dioxide (CO2) comparable to those found on Venus, suggesting a dense carbon-dominated atmosphere.
"The detected CO2 signal from the first study is tiny, and so it required careful statistical analysis to ensure that it is real," explained Ohno. "At the same time, we needed the physical and chemical insights to extract the true nature of GJ 1214 b's atmosphere from Schlawin's study."
Ohno developed theoretical models to simulate various scenarios for the planet's atmosphere. The models that best aligned with the observational data consistently pointed to a Venus-like carbon-dominated atmosphere, leading the researchers to describe GJ 1214 b as a "super-Venus."
Despite the compelling findings, the team acknowledges the limitations of their analysis. "It's equivalent to Leo Tolstoy's War and Peace. If I gave you two copies and changed one sentence in one of the books, could you find that sentence?" said Schlawin, emphasizing the challenges of interpreting the faint atmospheric signals.
Future studies are essential to confirm and expand upon these findings, further unraveling the mysteries of this common but poorly understood type of exoplanet.
Research Report:A Possible Metal-dominated Atmosphere below the Thick Aerosols of GJ 1214 b Suggested by Its JWST Panchromatic Transmission Spectrum
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