Astronomers have measured atmospheric motion around the equator of WASP-127b at close to 9 kilometres per second, about 33,000 kilometres per hour. The giant exoplanet is roughly 520 light-years away, yet its weather left a velocity fingerprint precise enough to separate gas moving towards Earth from gas moving away.
The result, obtained with the European Southern Observatory’s Very Large Telescope in Chile, is the fastest jet-stream motion of its kind measured on a planet. ESO compared it with winds of 1,800 kilometres per hour on Neptune, the Solar System’s wind record-holder. On that benchmark, WASP-127b’s maximum equatorial speed is more than 18 times greater.
No telescope photographed clouds racing around the distant world, and no probe carried an anemometer into its atmosphere. The measurement came from Doppler shifts in the spectral signatures of water vapour and carbon monoxide during a single transit. A model then connected those shifts to a rapidly rotating equatorial jet.
There is also a distinction hidden inside the 33,000-kilometre-per-hour headline. The peer-reviewed paper calculates a wind speed of 7.7 plus or minus 0.2 kilometres per second after subtracting the planet’s expected rotation. The higher figure describes the maximum atmospheric motion at the equator when the jet and rotation are combined.
WASP-127b is large, light and close to its star
WASP-127b was announced in 2016 and belongs to the loose family of intensely heated giant planets often called hot Jupiters. The NASA Exoplanet Archive places its star about 159.5 parsecs away, equivalent to roughly 520 light-years. The planet completes an orbit every 4.178 days at a distance near 0.05 astronomical units.
It is slightly wider than Jupiter but carries only a fraction of Jupiter’s mass. The archive’s adopted values give a radius about 1.31 times Jupiter’s, a mass near 0.165 Jupiter masses and an average density around 0.097 grams per cubic centimetre. That makes WASP-127b an exceptionally inflated world with an extended atmosphere.
A large atmospheric scale height is useful to astronomers. As the planet passes in front of its star, some starlight filters through the gas around its edge before reaching Earth. Atoms and molecules remove narrow sets of wavelengths from that light. Their motion also shifts those features towards shorter or longer wavelengths through the Doppler effect.
Two molecular peaks revealed opposite motions
The team used CRIRES+, a high-resolution infrared spectrograph mounted on one of the Very Large Telescope’s 8.2-metre units. The observations covered a transit in the infrared K band, where the researchers searched the changing spectrum for patterns expected from different atmospheric molecules.
Water vapour and carbon monoxide were both detected. Instead of producing one broad velocity peak, each molecule generated two distinct peaks. Part of the atmosphere was approaching the observers at high speed while another part was receding at a similar speed.
That is the signature expected when a fast equatorial flow crosses the two edges of the planet visible during transit. One limb carries absorbing gas partly towards Earth and the opposite limb carries it away. The peer-reviewed analysis in Astronomy & Astrophysics used a two-dimensional retrieval model to infer a supersonic eastward jet and weaker contributions from the poles.
The geometry is more informative than a simple wind-speed estimate. The two peaks correspond to the morning and evening terminators, the boundaries between the permanent day and night hemispheres. The polar signal was muted, which could mean that the poles are much cooler or that high clouds are blocking the molecular signatures there. The evidence also tentatively favours a morning terminator about 175 kelvin cooler than the evening one, although the uncertainty is large enough that the temperature difference is not a firm detection.
How 7.7 km/s becomes a 33,000 km/h headline
Researchers expect WASP-127b to be tidally locked, meaning one rotation takes the same 4.178 days as one orbit. That expectation has not been confirmed by a direct rotation measurement. Using the planet’s estimated radius and orbital period gives an equatorial rotation speed of about 1.6 kilometres per second.
The atmospheric retrieval found a total equatorial velocity near 9.3 kilometres per second. After removing the expected rotation, the team calculated the jet itself at 7.7 plus or minus 0.2 kilometres per second, equivalent to roughly 27,700 kilometres per hour.
ESO’s announcement rounded the maximum motion to 9 kilometres per second, or close to 33,000 kilometres per hour, and described that as the speed reached by the jet winds. That is the source of the widely reported figure. It captures the maximum rate at which atmospheric material is moving around the equator, while the paper’s 7.7-kilometre-per-second value isolates the flow relative to the assumed rotating planet.
Neither number was read directly from one shifted line. The researchers removed Earth’s atmospheric features and the star’s contribution, cross-correlated the remaining spectra with molecular templates, and fitted the paired signals with an atmospheric model. The unusually clean separation of the two peaks is what makes the inference powerful.
The “18 times Neptune” comparison uses 1,800 km/h
ESO set the 33,000-kilometre-per-hour value beside a Neptune wind speed of 0.5 kilometres per second, or 1,800 kilometres per hour. Dividing one by the other gives about 18.3, supporting the “more than 18 times” comparison in the title.
Planetary wind figures are often rounded, and different authoritative summaries use slightly different values. NASA describes Neptune’s winds as exceeding 2,000 kilometres per hour. Using 2,000 as the denominator produces a ratio of about 16.5. The comparison therefore depends on which rounded Neptune benchmark is chosen.
The physical conclusion is unchanged. Neptune has the fastest measured winds in the Solar System, and WASP-127b’s inferred equatorial motion is far faster. Comparing a remote exoplanet spectrum with clouds tracked by Voyager also involves different methods, so the multiplier is best understood as scale rather than laboratory precision.
The planet was not spatially resolved
An artist’s illustration can show a globe wrapped in a bright equatorial band, but the observations did not resolve WASP-127b into surface or cloud features. The planet and star remain essentially point sources. Researchers separated atmospheric regions by their different velocities, not by seeing those regions as pixels.
That limitation is also the achievement. A high-resolution spectrum encoded enough information to distinguish the two terminators and to infer that the poles contribute less strongly. The University of Göttingen’s account emphasises that the result offers a new test of global-circulation models for exoplanets. It also confirms water vapour and carbon monoxide in an atmosphere where earlier studies had disagreed about the carbon monoxide signal.
The word “supersonic” needs similar context. The relevant speed of sound depends on the local atmospheric composition and temperature. It is not a comparison with sound travelling through room-temperature air on Earth. The study’s classification refers to the expected sound speed in WASP-127b’s hot, hydrogen-rich atmosphere.
From a record to a method for mapping alien weather
SpaceDaily’s initial report on WASP-127b’s winds covered the record when the result appeared in January 2025. The deeper importance is what the observation demonstrates: atmospheric geography can be recovered from a planet too distant to image as a disc.
Ground-based instruments currently have an advantage for this work because they can deliver the extremely fine velocity precision required. ESO expects the Extremely Large Telescope and its planned ANDES spectrograph to resolve still finer patterns and extend the method towards smaller planets.
WASP-127b is an unusually favourable target, with a vast atmosphere and a very short orbit. Rocky worlds will be much harder. Even so, the double peaks show a path from detecting molecules to reconstructing circulation. The speed record is startling, but the ability to separate morning, evening, equator and poles in an unresolved exoplanet is the more durable result.