The James Webb Space Telescope (Webb) has cracked the case of the inflated exoplanet WASP-107 b, solving a long-standing mystery in exoplanet science.
This “warm Neptune” – a gas giant smaller and cooler than Neptune – has puzzled astronomers with its surprisingly large size for its relatively low mass.
Image: NASA, ESA, CSA, Ralf Crawford (STScI) Science: L. Welbanks (ASU) and the JWST MANATEE Team.
The Puffy Planet Problem
WASP-107 b boasts a radius exceeding three-quarters that of Jupiter, but holds less than one-tenth Jupiter’s mass, making it one of the least dense planets discovered. Many large, gassy exoplanets exist, but most are scorching hot and harbor substantial mass, easier to explain from a formation standpoint. WASP-107 b defied this trend. Astronomers struggled to reconcile the giant planet’s size with the cooler temperatures they expected based on its feeble mass. The prevailing theory suggested a small, rocky core surrounded by a massive, puffy atmosphere – a difficult scenario to explain given the limitations of core growth during planetary formation.
Webb Unveils a Hot and Energetic Interior
Combining Webb’s observations with previous data from Hubble, researchers made two key findings. First, they discovered surprisingly low levels of methane (CH4) in the exoplanet’s atmosphere. Normally, hot planets destroy methane molecules, and the lack of methane abundance pointed towards a significantly hotter interior than previously thought. This revelation challenged the entire theoretical framework for WASP-107 b.
Secondly, the data hinted at a much more massive core for WASP-107 b. Theorists suggest that this unexpected heat originates from tidal heating. WASP-107 b’s elliptical orbit subjects it to fluctuating gravitational forces as it circles its star, causing the planet to stretch and compress rhythmically. This relentless cosmic tug-of-war injects heat into the planet’s interior. Tidal heating, previously considered a possibility, gained credence with Webb’s data.
A New Model for Puffy Exoplanets
The scorching internal temperature explains WASP-107 b’s puffiness without resorting to exotic formation theories. Imagine a giant balloon filled with hot air – the ballooned appearance of WASP-107 b is likely a consequence of its inflated internal temperature. This newfound understanding can be applied to dozens of similar low-density exoplanets, potentially resolving a longstanding enigma in exoplanet research. By demonstrating that tidal heating can inflate a cooler exoplanet, Webb has broadened our perspective on how these gas giants can evolve.
Webb’s Spectroscopic Prowess
Webb’s extraordinary sensitivity to light passing through exoplanet atmospheres proved to be the game-changer. By analyzing the minuscule absorption patterns in starlight filtering through WASP-107 b’s atmosphere, scientists were able to identify the presence of various molecules, including water vapor, carbon dioxide, and ammonia. The surprisingly low abundance of methane was the key that unlocked the secret to the planet’s inflated state. Prior telescopes lacked the resolution to perform such detailed atmospheric analysis on distant exoplanets.
A Denser Core: A More Plausible Formation Story
The spectral analysis also provided clues about the size of the core. The scarcity of methane indicated vigorous mixing between the hot interior and cooler upper atmosphere. When combined with the knowledge of the total internal energy, scientists were able to estimate the ratio of light elements (hydrogen and helium) to heavier elements (carbon, nitrogen, etc.) within the planet. This calculation yielded a core mass at least twice what was previously assumed. A heftier core aligns better with current theories of planet formation, making WASP-107 b’s story more plausible. Previously, the small core hypothesis didn’t fit neatly with established models of planetary development.
Webb: A Stepping Stone to Further Discoveries
The Webb telescope’s scrutiny of WASP-107 b is a testament to its remarkable capabilities. This discovery revolutionizes our understanding of inflated exoplanets and paves the way for the investigation of numerous similar celestial bodies. With Webb as our guide, we embark on a journey of exoplanetary exploration, unveiling the secrets held within these distant and intriguing worlds. Webb’s ability to peer into exoplanet atmospheres ushers in a new era of discovery, promising to rewrite our textbooks on planetary formation and evolution. This is just the beginning of a thrilling adventure into the cosmos, fueled by the unprecedented power of the James Webb Space Telescope.
