JWST maps the weather on a hot gas giant 700 light-years away
The James Webb Space Telescope (JWST) study published in Nature Astronomy this month made the atmospheric dynamics of the exoplanet WASP-43b visible. At 700 light-years from Earth, in the constellation Puppis, WASP-43b is a "hot Jupiter" class gas giant orbiting very close to its star. JWST's observations show, in detail for the first time, how varied the atmospheric conditions on the planet can be across an Earth year.
WASP-43b was discovered in 2011. The planet sits in an environment unlike any in our Solar System: it orbits its star in 22 hours and is tidally locked, always presenting the same face to its star. The star-facing side is its day, the other its night. Earlier Hubble observations measured the temperature difference between these two halves at roughly 1,700°C; but they could not fully resolve the dynamics between them.
JWST's Mid-Infrared Instrument (MIRI) took measurements across 23 different rotations of the planet over the equivalent of one Earth year. The total observation time of 7,000 hours allowed the science team to map atmospheric composition, temperature variation and wind speeds in three dimensions. The lead author, Professor Hannah Wakeford of the University of Bristol, said: "This is the first time we have built a complete atmospheric picture of an exoplanet."
The measurement results are striking. On the planet's day side, temperatures range from 1,250°C to 1,730°C; the hottest region is on the eastern hemisphere. On the night side, the average ranges from -50°C to 220°C. Air currents at the day-night boundary reach speeds of 9,000 km/h — several times faster than any wind known in the Solar System. JWST data confirmed for the first time the presence of silicate (sand) clouds in the upper atmosphere of the night side.
In terms of atmospheric chemistry, JWST's spectroscopic analysis detected water vapour (H₂O), carbon monoxide (CO), carbon dioxide (CO₂) and sulphur dioxide (SO₂). Methane (CH₄) is at much lower levels than expected — a significant finding for the planet's atmospheric thermodynamics. University of Bristol planetary scientist Dr Laura Kreidberg said: "The dominance of carbon monoxide signals that the planet's thermodynamic equilibrium is different from that of Jupiter and Saturn."
The cloud structure is an important technical finding. Hubble observations had suggested a cloudless atmosphere on the day side of WASP-43b, but JWST showed active silicate cloud formation on the night side. These clouds modify thermal reflection of the temperature and directly influence how the planet's energy from the star drives atmospheric dynamics. A persistent cloud layer was detected on the night side from the upper troposphere to mid-stratosphere.
The study's broader implications speak to how common the hot Jupiter class is in our universe and how it should be modelled. Of the more than 5,500 exoplanets identified to date, around 400 fall in the hot Jupiter class. The detailed JWST work on WASP-43b provides foundational data for atmospheric models of this class. The European Space Agency (ESA) plans similar atmospheric mapping for 12 other hot Jupiter exoplanets in JWST's projected 2027 observing programme.
Dr Klaus Pontoppidan, JWST project science director at NASA Goddard Space Flight Center, said the study "will lead to a new understanding of comparative planetary science." According to Pontoppidan, an important step toward discovering Earth-like exoplanets is to understand how atmospheric dynamics can be mapped. The WASP-43b study sets the methodology for the atmospheric studies JWST will undertake over the next decade.
In Türkiye, the TÜBİTAK National Observatory (TUG) in Antalya is supporting JWST's atmospheric mapping programme with pre-observation telescope work. TUG's 1.5-metre RTT-150 provides ground-based observations of hot-Jupiter-class exoplanets. Bosphorus University astronomy professor Dr Necmi Şenay said the observation programme between TÜBİTAK and ESA has expanded in 2026.
Exoplanet science has evolved rapidly over the past decade. In 2014 the number of confirmed exoplanets was under 1,000; today it exceeds 5,500. JWST, NASA's TESS satellite, ESA's CHEOPS satellite and the upcoming ESA Ariel mission (2029) are expected to push the number past 10,000 over the next five years. The JWST work on WASP-43b marks a turning point not only in count but in the quality of atmospheric data gathered.
The study's next phase is the planned March 2027 upgrade of JWST's Mid-Infrared Instrument. The new MIRI-2 will double the precision of atmospheric mapping. In that process, WASP-43b will be re-observed; reference data will be gathered to determine whether atmospheric changes on the planet are taking place over the equivalent of two Earth years. For the astronomy community, WASP-43b is now a central reference planet within comparative planetary science.
JWST's work makes visible the wealth of data that frontier space science offers to the global community, including Türkiye. For astronomy students, atmospheric mapping technology will be one of the career fields of the coming decade. Universities adding this topic to their curricula from 2027 include MIT, Cambridge, Heidelberg and Istanbul University.