JWST Reveals Cloud Cycle on WASP-94A b 700 Light-Years Away

Q: How many exoplanets have we misjudged because older telescopes couldn't see through their morning clouds?

No one knows yet, but the confirmed count is at least one and likely more. JWST has definitively shown that WASP-94A b was misread by earlier, lower-resolution observations. Hubble-era data averaged the planet’s cloudy morning side and clearer evening side into a single spectrum, which made its oxygen and carbon abundances look wildly inflated. JWST’s limb-by-limb view corrected that, cutting the estimate from “hundreds of times solar” to roughly five times solar. The broader implication is that this is probably not an isolated case. The same Johns Hopkins team has already identified similar morning-cloud/evening-clear patterns on two other hot Jupiters, WASP-39 b and WASP-17 b. That strongly suggests older composition estimates for those planets may also be biased, though the reporting stops short of saying all three have been fully reclassified to the same degree as WASP-94A b. So the safest evidence-based answer is that at least one exoplanet has been clearly misjudged, and at least two more are strong candidates. Beyond that, researchers say many previously studied hot Jupiters could need revision because older telescopes such as Hubble could not separate cloudy and clear limbs during transit. JWST is only now making that possible, so the true number remains unknown.

3 articles · Updated · physicsworld.com · Jun 15

Johns Hopkins researchers used JWST transit data to separate WASP-94A b’s morning and evening atmospheres, finding thick clouds at dawn and much clearer skies by evening.
Clouds likely condense on the planet’s permanently colder nightside, then winds push them toward the morning edge before heat on the dayside makes them evaporate or sink.
The split view also revised the planet’s chemistry: oxygen and carbon now appear about five times solar, not the hundreds of times inferred from earlier averaged spectra.
The result, published in Science, is part of JWST’s Grand Tour Program and has already been echoed on two other hot Jupiters—WASP-39 b and WASP-17 b.
Using WASP-94A b as a benchmark, the team is set to receive more than 180 hours of new JWST time to compare weather patterns across exoplanets.

Sources

physicsworld.com1d ago

JWST Discovers Planet-Wide Cloud Cycle on Exoplanet WASP-94A b with Cloudy Mornings and Clear Evenings

Eos1d ago

A Hot Jupiter's Cloudy Mornings and Clear Evenings Provide Clues to Its Chemistry - Eos

spacedaily.com1d ago

JWST just mapped the morning weather on a planet 690 light-years away, and the forecast of sand-like clouds exposed a 100-fold bias in how exoplanet atmospheres have been read for more than

4 Sources

Beyond sand clouds, what other extreme alien weather will the James Webb Space Telescope reveal next?

How many exoplanets have we misjudged because older telescopes couldn't see through their morning clouds?

Could these alien weather cycles rewrite our fundamental theories about how solar systems form?

Daily Cloud Cycle Discovered on WASP-94A b: JWST Reveals Dynamic Weather and Refines Exoplanet Atmospheric Models

Overview

The James Webb Space Telescope (JWST) has revealed a dramatic daily cloud cycle on the exoplanet WASP-94A b, a tidally locked gas giant where one side always faces its star and the other remains in darkness. This creates extreme temperature differences across the planet. By observing WASP-94A b as it transited its star, JWST measured the atmosphere on both the morning side, where clouds form and move from the cool nightside, and the evening side, where clouds disappear in the intense heat. These observations mark a major step in understanding dynamic weather and atmospheric composition on distant worlds.

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