JWST Decodes Daily Weather on Exoplanet WASP-94A b

Relevance: GS Paper III — Science & Technology (Space; awareness in space technology)

Source: Journal Science, 21 May 2026

1 · Context

The National Aeronautics and Space Administration (NASA) James Webb Space Telescope (JWST) has, for the first time, mapped a daily weather cycle on a planet outside our solar system. The exoplanet WASP-94A b, nearly 700 light-years away, has cloudy mornings and clear evenings.

2 · About WASP-94A b

• Type: a ‘Hot Jupiter’ — a gas giant orbiting very close to its parent star.
• Size & mass: roughly twice the size of Jupiter but only half its mass.
• Orbital period: just four Earth days per revolution.
• Tidally locked: like our Moon, one face is in permanent day (hot enough to melt rock); the other in permanent night (near absolute zero).

3 · The daily weather cycle

WASP-94A b · ONE ROTATION

NIGHT SIDE · cool, dark Permanent darkness, near absolute zero. Rock vapour condenses into clouds of magnesium silicate, iron and magnesium sulphide.

↓

MORNING · cloudy Extremely fast winds sweep the rock clouds from the night side onto the morning side.

↓

DAY SIDE · scorching Sweltering — hot enough to melt rock. The incoming clouds vaporise.

↓

EVENING · clear skies No clouds left. JWST reads the true atmospheric chemistry without bias.

4 · How JWST studied it

• Transit method: the planet passes in front of its star, briefly dimming the starlight.
• Transmission spectroscopy: during the transit, starlight filters through the planet’s atmosphere; each gas absorbs specific wavelengths, leaving chemical fingerprints.

5 · Why it matters

• Earlier averaged atmospheric estimates were biased; clouds masked the true composition.
• Separating cloudy morning data from clear evening data gives a more accurate chemical profile.
• Improves models used to detect habitable conditions and biosignatures on other worlds.

VALUE BOX · QUICK REVISION Recent event: 1-metre meteor energy not relevant — this is WASP-94A b, 700 light-years away. Hot Jupiter facts: twice Jupiter’s size, half its mass, 4-day orbit, tidally locked. Rock clouds composition: magnesium silicate, iron, magnesium sulphide. Method used: Transit method + Transmission spectroscopy. India’s space astronomy: TMT (partner), AstroSat (2015), Aditya-L1 at Lagrange Point 1.

MCQ · PRELIMS PRACTICE

With reference to the recent study of the exoplanet WASP-94A b, consider the following statements:

1. It is classified as a ‘Hot Jupiter’ because it is twice the mass of Jupiter and completes one orbit around its star in just four Earth days.
2. The clouds detected in its atmosphere are made mainly of magnesium silicate, iron and magnesium sulphide.
3. Its atmosphere was studied using the transit method combined with transmission spectroscopy.

Which of the statements given above are correct?

(a) 1 and 2 only	(b) 2 and 3 only
(c) 1 and 3 only	(d) 1, 2 and 3

Answer: (b) 2 and 3 only

Statement 1 — Incorrect (the trap). The size–mass relationship is reversed. WASP-94A b is roughly twice the size of Jupiter, but only half its mass. The four-day orbit is correct, but the wrong physical parameter breaks the statement.

Statement 2 — Correct. JWST detected morning-side ‘rock clouds’ of magnesium silicate, iron and magnesium sulphide.

Statement 3 — Correct. JWST used the transit method and transmission spectroscopy to read chemical fingerprints in the filtered starlight.