Supersonic jet stream detected at the equator of a giant exoplanet

Just a few years ago, it was only possible to determine two key characteristics of exoplanets: their mass and radius. However, recent technological advancements have opened an entirely new window into the study of these worlds beyond our solar system. State-of-the-art instruments, such as CRIRES+, a high-resolution cryogenic infrared spectrograph—specifically developed to search for and characterize potentially habitable super-Earth-type exoplanets—allow for detailed exploration of the dynamics and composition of their atmospheres. Thanks to this technology, a recent study, in which the Instituto de Astrofísica de Andalucía (IAA-CSIC) participated and was published in the journal Astronomy & Astrophysics, has led to the discovery of a powerful jet stream circulating at supersonic speed around the equator of the exoplanet WASP-127b. "This is the fastest wind ever measured on any known planet to date," says Lisa Nortmann, a researcher at the University of Göttingen, Germany, who leads the work.

Artist’s impression of supersonic winds on WASP-127b. Credit: ESO/L. Calçada

This leap in precision brings us closer to better understanding the conditions under which Earth-like planets could arise. "Hot Jupiter-type planets are something we don't have in our Solar System. Studying their atmospheres in great detail is a way to understand the chemical and dynamic processes that led to the formation of these extraordinary planets and to test our theoretical models in unique cases like that of WASP-127b," highlights Denis Shulyak, a researcher at the Institute of Astrophysics of Andalusia and co-author of the article.

WASP-127B: A GIANT EXOPLANET WITH AN ORBIT VERY CLOSE TO ITS STAR

The international team studied the atmosphere of the exoplanet WASP-127b using high-resolution infrared spectroscopy. WASP-127b is a type of exoplanet known as a "hot Jupiter" because it has a size similar to Jupiter in our own Solar System but is much less massive: it has only one-sixth of its mass and a much higher atmospheric temperature. This high temperature is due to a very short orbital distance, as WASP-127b is one hundred times closer to its host star—a G-type star—than Jupiter is to the Sun.

Its discovery was announced in 2016 and remains an interesting object of study, as its extreme characteristics make it a natural laboratory for understanding how giant planets form and evolve in systems different from our own.

Artist's impression of the exoplanet WASP-127b orbiting its G-type star 520 light years from Earth. Credits:NASA (https://science.nasa.gov/exoplanet-catalog/wasp-127-b/)

SUPERSONIC WIND AND ATMOSPHERIC VARIATIONS

Due to the planet's distance, which prevents direct observation from Earth, and the intense brightness of its star, which obscures any light emitted by the planet itself, the team resorted to an indirect approach for its study. When the planet passes in front of its star, part of the star's light passes through the planet's atmosphere. By analyzing and comparing the light received before and during the exoplanet's transit through the star's disk, the scientific team was able to reconstruct the planet's atmospheric properties.

The results confirm the presence of water vapor and carbon monoxide in the atmosphere of WASP-127b. Additionally, to the researchers' surprise, detailed analyses of the spectral line shapes demonstrated a double-peaked velocity profile in the atmospheric material. This discovery indicates that part of the atmosphere moves toward us at an astonishing speed of 9 km per second, while another part moves away from us at the same speed, suggesting the presence of a powerful jet stream circulating at supersonic speed around the planet's equator. This jet moves nearly six times faster than the planet's rotation. "This is something we had never observed before," notes Lisa Nortmann (University of Göttingen). In comparison, the fastest wind measured in the Solar System was found on Neptune, moving at 0.5 km per second.

At the same time, the data revealed weaker signals from the planet's poles, indicating colder conditions compared to the equator and confirming the presence of significant latitudinal variations in its atmosphere. Although this had been observed on other planets in our Solar System, studying such variations in exoplanets had been a challenge until now.

Dr. Artie Hatzes, principal investigator of the CRIRES+ instrument and part of the research team, states that capturing these details of atmospheric material velocity on an exoplanet is only possible with high-resolution spectroscopy on a large telescope. "This discovery highlights one of the reasons we built CRIRES+. Our ability to use it to resolve the fine details of exoplanet atmospheres gives us a better understanding of these distant worlds and complements the findings of space telescopes."

Astronomers have measured supersonic jet winds on WASP-127b, a giant gas planet located about 520 light-years from Earth. It is the fastest jetstream of its kind ever measured in the Universe, with speeds up to 9 km per second. The team mapped the weather of WASP-127b using the CRIRES+ instrument on the European Southern Observatory’s Very Large Telescope (ESO’s VLT). Credit: ESO

The results of this study pave the way for future research on exoplanet atmospheres, laying the groundwork for high-resolution spectroscopy in future instruments like ANDES, which will be installed on the Extremely Large Telescope (ELT) of ESO. The observational data will also help guide future theoretical work, especially in predicting how gas giants—massive planets primarily composed of gases—circulate heat and chemicals.

The work demonstrates how high-resolution instruments like CRIRES+ allow astronomers to map the climate patterns of distant worlds, even without being able to directly observe their surfaces. WASP-127b, with its unique atmospheric characteristics and fast winds, provides a comprehensive case study on atmospheric dynamics in planets located beyond our Solar System.