Cloudy Mornings And Clear Evenings On Giant Extrasolar World WASP-94A b
Aerosols are common in exoplanet atmospheres, but their formation-whether through gas condensation or photochemical reactions-remains uncertain.
We report a 6σ detection of limb asymmetry in the transmission spectrum of WASP-94A b, revealing a cloud-covered (11σ) cooler morning limb and a clear hotter evening limb with strong H2O absorption (10σ).
Models suggest cloud droplets formed near mbar pressures are lofted to 0.01 mbar by strong vertical dynamics in the morning limb. They evaporate when circulated to the hotter evening limb, requiring a minimum 280 K (3σ) limb-to-limb temperature difference.
We confirm that aerosols in hot Jupiters like WASP-94A b can have clouds cycling between day and night sides instead of photochemical hazes. Ignoring these effects severely biases inferred chemical abundances, showing limb-resolved spectroscopy is critical for characterizing the formation mechanisms of transiting exoplanets-from gas giants to terrestrial exoplanets, indicating the need to reassess inferences from a decade’s worth of Hubble Space Telescope observations.
Transmission spectrum of the morning and evening limbs of WASP-94A b. (A) shows the observing geometry of the two limbs of WASP-94A b and its host star (to scale). (B) shows the nightside cloud map of WASP-94A b predicted through a 3D general circulation model. (C) shows the observed transmission spectrum of the evening terminator of the planet with red points along with the best-fit model. The key atmospheric absorbers shaping the observed spectrum (H2O, clouds, etc) are shown with the shaded colors. (D) shows the observed transmission spectrum of the morning terminator with blue points along with the best-fit model. The spectrum is mainly shaped by cloud scattering as has been shown with the gray shaded region. — astro-ph.EP
Sagnick Mukherjee, David K. Sing, Guangwei Fu, Kevin B. Stevenson, Stephen P. Schmidt, Harry Baskett, Patrick McCreery, Natalie H. Allen, Katherine A. Bennett, Duncan A. Christie, Carlos Gascón, Jayesh Goyal, Éric Hébrard, Joshua D. Lothringer, Mercedes López-Morales, Jacob Lustig-Yaeger, Erin M. May, L. C. Mayorga, Nathan Mayne, Lakeisha M. Ramos Rosado, Henrique Reggiani, Zafar Rustamkulov, Kevin C. Schlaufman, K. S. Sotzen, Daniel Thorngren, Le-Chris Wang, Maria Zamyatina
Comments: Submitted, 31 pages, 26 Figures, 7 Tables
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2505.10910 [astro-ph.EP] (or arXiv:2505.10910v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2505.10910
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Submission history
From: Sagnick Mukherjee
[v1] Fri, 16 May 2025 06:31:00 UTC (24,462 KB)
https://arxiv.org/abs/2505.10910
Astrobiology,
