Cloudy mornings and clear evenings on a gas giant exoplanet
Summary
The spectra of exoplanet atmospheres are affected by aerosols (clouds and hazes) of uncertain origin. Proposed aerosol formation mechanisms include gas condensation or photochemical reactions. We measured the transmission spectrum of the tidally locked gas giant exoplanet WASP-94A b and identified asymmetry in its atmosphere. The morning limb is cooler and cloudy, whereas the evening limb is hotter and exhibits gaseous water absorption features. We interpret this difference as being due to
Content
# Cloudy mornings and clear evenings on a gas giant exoplanet
*Published: 2026 May 21*
The spectra of exoplanet atmospheres are affected by aerosols (clouds and hazes)
of uncertain origin. Proposed aerosol formation mechanisms include gas
condensation or photochemical reactions. We measured the transmission spectrum
of the tidally locked gas giant exoplanet WASP-94A b and identified asymmetry in
its atmosphere. The morning limb is cooler and cloudy, whereas the evening limb
is hotter and exhibits gaseous water absorption features. We interpret this
difference as being due to the formation of cloud droplets near the morning
limb, which evaporate during circulation to the evening limb. The dominant
aerosols are clouds cycling between the day and night sides of the atmosphere,
not photochemical hazes. The resulting asymmetry can severely bias chemical
abundance measurements, unless limb-resolved spectroscopy is available.
DOI: 10.1126/science.adx5903