The James Webb Space Telescope (JWST) has provided a unique weather report for a planet located 690 light-years away. The forecast for WASP-94A b, a tidally locked gas giant, reveals cloudy mornings of vaporized rock, clear evenings, and strong winds that can move sand-like particles before they evaporate under constant daylight.
WASP-94A b has a mass slightly less than half that of Jupiter but is more than 70% wider. With an average temperature above 1,500 Kelvin, one side of the planet remains in perpetual daylight, while the other is shrouded in permanent night. This creates a significant temperature difference, causing the evening limb to be around 450 Kelvin hotter than the morning limb. This leads to distinct atmospheric conditions on each side.
The JWST discovered that the morning atmosphere consists of thick clouds made of vaporized magnesium silicate, while the evening skies are clear. Powerful winds move these magnesium silicate clouds from the cool night side to the hot day side, where they evaporate before reaching the evening limb.
The findings suggest that the weather on WASP-94A b is constantly changing, resembling a sandstorm in the sky. This has broader implications for how astronomers study exoplanets. Traditionally, data averaged from the whole planet led to errors in estimating chemical compositions. The JWST’s methods can now differentiate between the morning and evening atmospheres, revealing more accurate insights.
Mukhurjee’s team intends to use this advanced technique on more planets, including one with an unusual orbit, which could provide new insights into varied weather systems. The research underscores the complexity of exoplanets, highlighting that what appears as a single point of light may actually be two distinct atmospheres.
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