← No. 019 SUN 18 OCT 2026

A hot Jupiter has cloudy mornings and clear evenings.

WASP‑94A b

Using JWST during a transit, astronomers separated the planet’s morning edge from its evening edge. The morning side looked cooler and veiled by high clouds; the evening side was hotter, with clearer water‑vapor features. The pattern fits a daily cycle in which mineral clouds form overnight and thin toward dusk. Published May 21, 2026 in Science, it shows how limb‑resolved views cut bias in exoplanet atmospheres.

Why it’s interesting

Fig. 019 Starlight skimming a planet’s rim, with dense scattering at the morning edge and cleaner paths at the evening edge.

Why it’s interesting

We usually imagine a distant planet as one uniform disk. This shows that even its two edges can live different days—and that clouds can hide key gases if we only average the whole globe.

The longer version

Hot Jupiters are expected to have fierce day–night contrasts and fast winds, but most measurements blur a whole world into one average spectrum. During a transit of WASP‑94A b, JWST’s NIRISS mode separated the planet’s morning (leading) edge from its evening (trailing) edge. The morning limb appeared cooler and cloud‑shrouded; the evening limb showed stronger water‑vapor absorption and higher temperatures.

The asymmetry is detected at high significance (about six standard deviations), with water present at roughly ten sigma and clouds inferred at about 9.7 sigma. Cloud models moderately favor magnesium‑silicate (enstatite) grains over generic hazes, though no single mineral is directly identified. The snapshot matches a simple picture: clouds condense on the night/morning side and thin or evaporate toward the day/evening side.

Edition: No. 019
Date: Sunday 18 October 2026
Subject: WASP‑94A b
Period: May 21, 2026
Field: space
Evidence: 4 sources, 2 primary

See how we got here

Found after 25 research paths · Selected from 6 candidates

01 Exoplanet weather Skies and winds on worlds beyond our system.
02 Hot Jupiters Tidally locked giants with permanent day and night.
03 Transits Starlight filters through a planet’s thin rim.
04 Limb‑resolved spectra Morning and evening edges measured separately with JWST/NIRISS.
05 WASP‑94A b Morning looks cooler and cloudier; evening hotter and clearer.
→ A hot Jupiter has cloudy mornings and clear evenings.

Sources

Nothing publishes without independent sources. How we verify →

1
Cloudy mornings and clear evenings on a gas giant exoplanet (author’s version; Science 392, 858–862, 2026)
AAAS/Science (author’s OA on arXiv) · 2026 · peer reviewed Primary

Study existence, date, journal/volume/pages; abstract language about cloud formation near morning limb and evaporation toward evening; limb-resolved method; bibliographic details.

arxiv.org
2
Cloudy mornings and clear evenings on a gas giant exoplanet (HTML)
arXiv (HTML of the same paper) · 2026 · peer reviewed Primary

Details: cannot determine exact species from spectrum; enstatite (MgSiO3) cloud model moderately preferred; detection significances (~6σ limb asymmetry; 10σ H2O; 9.7σ clouds).

arxiv.org
3
Astronomers de‑fog exoplanet atmospheres with new cloud‑detecting method
Johns Hopkins University · 2026 · university

Plain‑language summary on May 21, 2026; states mornings are clouded by magnesium‑silicate aerosols and evenings are clear; contextualizes significance and reduced abundance bias.

hub.jhu.edu
4
This exoplanet weather forecast by the James Webb Space Telescope calls for sandy skies and a clear (alien) sunset
Space.com · 2026 · journalism

Independent coverage on May 21, 2026 describing cloudy mornings and clear evenings on WASP‑94A b; frames result as first daily cycle seen on a hot Jupiter.

space.com

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