On January 9, 2025, astronomers utilizing the James Webb Space Telescope (JWST) made significant strides in exoplanet research by analyzing the atmospheric composition of WASP-166 b, a hot super-Neptune located approximately 0.067 astronomical units from its host star.
WASP-166 b, which is about seven times the diameter of Earth and 32 times its mass, completes an orbit around its star in just 5.44 days, indicating its close proximity to the star. This results in an equilibrium temperature estimated at 1270 Kelvin, categorizing it within the 'hot Neptune desert,' a region where such planets are rarely found due to stellar radiation.
The host star, WASP-166, is classified as F9V and is approximately 20% larger and more massive than the Sun, with an effective surface temperature of 6050 Kelvin and a metallicity of 0.19 dex. At 2.1 billion years old, it is considered relatively young.
Astronomers, led by Andrew W. Mayo from San Francisco State University, employed the NIRISS spectrograph and NIRCam camera to investigate the atmosphere of WASP-166 b. Their findings revealed a rich atmosphere containing water vapor and carbon dioxide, along with traces of ammonia at lower concentrations.
Additionally, the analysis indicated that the atmosphere is primarily composed of helium and hydrogen in ratios typical of the primordial solar nebula. Notably, no signs of carbon monoxide were detected.
The carbon-to-oxygen ratio on WASP-166 b was found to be 0.282, significantly lower than that of its host star (0.41) and the Sun (0.55), suggesting a unique formation process. The atmosphere's metallicity was measured at 1.57 dex.
Researchers speculate that WASP-166 b formed through the accretion of planetesimals, with possible core erosion or atmospheric photo-evaporation contributing to its current chemical profile.
This discovery adds to the ongoing exploration of exoplanets, enhancing our understanding of planetary formation processes in the universe and potentially addressing the question of whether we are alone in the cosmos.