Astronomers using the European Southern Observatory’s Very Large Telescope in Chile have measured an equatorial jet stream on the giant exoplanet WASP-127b reaching maximum equatorial motion of up to 33,000 kilometres per hour. Located roughly 520 light-years from Earth, this bloated gas world features atmospheric winds compared to Neptune’s 1,800 kilometres per hour gusts, which are the fastest found in our own Solar System.
Decoding the Velocity Fingerprint of WASP-127b
No telescope photographed cloud decks racing across the distant world, and no robotic probe deployed an anemometer into its upper layers. Instead, researchers extracted this velocity data from a single transit event. As WASP-127b passed directly in front of its host star, starlight filtered through the margins of the planet’s extended atmosphere. Atoms and molecules absorbed narrow slices of that light, while the Doppler effect shifted those spectral signatures toward shorter or longer wavelengths depending on whether the gas was moving toward or away from Earth.
The observation relied heavily on CRIRES+, a high-resolution infrared spectrograph mounted on an 8.2-metre unit of the Very Large Telescope. By zeroing in on the infrared K band, the research team isolated patterns corresponding to water vapour and carbon monoxide. Rather than generating a single broad velocity peak, each molecule produced two distinct spikes. One side of the planetary limb carried absorbing gas toward Earth, while the opposing limb swept gas away.
Unpacking the 33,000 km/h Figure and Planetary Rotation
The headline-grabbing metric requires careful engineering context. SpaceEyeNews notes that the atmospheric retrieval model calculated an overall equatorial motion of approximately 9.3 kilometres per second, equating to roughly 33,500 km/h (commonly rounded to 33,000 km/h). However, raw atmospheric motion combines wind speed with planetary rotation.
Announced in 2016, WASP-127b completes an orbit every 4.178 days at an orbital distance of roughly 0.05 astronomical units, according to the NASA Exoplanet Archive. Because of this tight orbit, the planet is assumed to be tidally locked. Factoring in an estimated rotational speed of roughly 1.6 kilometres per second, the peer-reviewed study published in Astronomy & Astrophysics isolates the jet-stream speed at 7.7 plus or minus 0.2 kilometres per second—roughly 27,700 km/h relative to the rotating body.
WASP-127b’s physical architecture makes this high-precision spectroscopy possible. NASA records its radius at approximately 1.31 times that of Jupiter, yet it carries roughly 0.165 Jupiter masses. This yields an average density of roughly 0.097 grams per cubic centimetre. This expansive scale height puffs out the atmosphere, amplifying the signal-to-noise ratio during transit observations.
Mapping Terminators and Asymmetric Weather
Beyond raw velocity, the two-dimensional retrieval model enabled researchers to model the boundaries between the permanent day and night hemispheres. The morning and evening terminators revealed distinct atmospheric behaviors. The data tentatively points toward a morning terminator approximately 175 kelvin cooler than the evening side, though uncertainties remain high. Meanwhile, polar signals appeared muted, suggesting either significantly lower temperatures at the poles or obscuring high-altitude cloud decks masking the underlying molecular signatures.
By bypassing direct imaging and leveraging high-resolution spectroscopy, this observation demonstrates how modern ground-based facilities can dissect the meteorology of distant worlds. As instrumentation like CRIRES+ continues to mature, mapping the complex fluid dynamics of hot Jupiters shifts from theoretical modeling to empirical reality.
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