WASP-94Ab is a hot-jupiter gas giant located ~690 light-years from Earth in the constellation Microscopium. It became the first exoplanet on which a repeating daily weather cycle was confirmed, reported by sagnick-mukherjee and david-sing in Science (May 21, 2026) using jwst’s NIRISS instrument and limb-resolved transmission-spectroscopy (src-jwst-wasp-94ab-weather-cycle-2026-05).
Properties
| Parameter | Value |
|---|---|
| Distance | ~690 light-years |
| Radius | 1.72 R_Jup |
| Mass | ~0.45 M_Jup |
| Orbital period | 3.95 days |
| Orbital distance | ~5.1 million miles (closer than Mercury to the Sun) |
| Surface temperature | >2,200 °F (1,200 °C) |
| Rotation | Tidally locked (permanent day/night sides) |
Daily weather cycle
- The permanent morning (leading) limb is blanketed in thick magnesium-silicate clouds (vaporized rock), detected at 9σ.
- The evening (trailing) limb is clear, showing water-vapor absorption at 10σ.
- The evening limb runs ~450 K hotter than the morning limb.
- Proposed mechanism: clouds condense on the cool nightside, ride equatorial super-rotation winds to the morning terminator, then sink or evaporate as they cross into the dayside.
Why it matters
Separating the two limbs corrected a decade of cloud-contaminated, full-disc data. WASP-94Ab’s inferred oxygen and carbon abundance dropped from “hundreds of times” Jupiter’s to only ~5× Jupiter’s — a value consistent with standard gas-giant formation. The blended-limb vs limb-resolved estimates differ at >4σ. The same cloud-cycle pattern was later found on WASP-39b and WASP-17b, suggesting pre-JWST hot-Jupiter composition estimates may be systematically biased. See exoplanet-atmosphere-models and the biosignatures caveat on limb-asymmetry averaging bias.
A sibling jwst limb-resolved finding — a dawn–dusk atmospheric asymmetry on the ultra-hot Jupiter wasp-121b (Gapp et al., Nature Astronomy, 2026) — independently reinforces that blended-disc methods miss longitudinal structure (src-jwst-wasp-121b-dawn-dusk-2026-06).