NASA’s Hubble observes the evolution of an exoplanet’s atmosphere over 3 years

By combining several years of observations from NASA’s Hubble Space Telescope and performing computer modeling, astronomers have found evidence of massive cyclones and other dynamic weather activity swirling on a hot, Jupiter-sized planet located 880 light years.

The planet, called WASP-121 b, is not habitable. But this result constitutes an important first step in the study of weather patterns on distant worlds, and perhaps eventually in the discovery of potentially habitable exoplanets with long-term stable climates.

Over the past decades, detailed telescope and satellite observations of neighboring planets in our solar system show that their turbulent atmospheres are not static but constantly changing, just like the weather on Earth. This variability should also apply to planets around other stars. But it takes a lot of detailed observations and computer modeling to actually measure these changes.

To make this discovery, an international team of astronomers collected and reprocessed Hubble observations of WASP-121 b taken in 2016, 2018 and 2019.

They discovered that the planet has a dynamic atmosphere that changes over time. The team used sophisticated modeling techniques to demonstrate that these dramatic temporal variations could be explained by weather conditions in the exoplanet’s atmosphere.

The team found that WASP-121 b’s atmosphere has notable differences between observations. The most dramatic thing is that there could be massive weather fronts, storms and massive cyclones that would be created and destroyed repeatedly due to the large temperature difference between the star-facing side and the dark side of the planet. exoplanet. They also detected an apparent shift between the hottest region of the exoplanet and the point on the planet closest to the star, as well as variability in the chemical composition of the exoplanet’s atmosphere (such as measured by spectroscopy).

The team reached these conclusions by using computer models to help explain the observed changes in the exoplanet’s atmosphere. “The remarkable details of our simulations of exoplanet atmospheres allow us to accurately model the weather on ultra-hot planets like WASP-121 b,” explained Jack Skinner, a postdoctoral researcher at the California Institute of Technology in Pasadena, in California, and co-leader of the study. of this study. “Here, we take a significant step forward by combining observational constraints with atmospheric simulations to understand time-varying weather conditions on these planets.”

“This is an extremely exciting result as we move forward in observing weather patterns on exoplanets,” said one of the team’s lead researchers, European Space Agency researcher Quentin Changeat. at the Space Telescope Science Institute in Baltimore, Maryland. “Studying exoplanet weather is essential for understanding the complexity of exoplanet atmospheres on other worlds, particularly in the search for exoplanets with habitable conditions.”

The work is published on the arXiv preprint server.

WASP-121 b is so close to its parent star that the orbital period is only 1.27 days. This proximity means the planet is tidally locked, so the same hemisphere always faces the star, in the same way that our Moon always has the same side pointing toward Earth. Daytime temperatures approach 3,450 degrees Fahrenheit (2,150 degrees Kelvin) on the star-facing side of the planet.

The team used four sets of archival Hubble observations of WASP-121 b. The full dataset included observations of WASP-121 b transiting in front of its star (taken in June 2016); WASP-121 b passing behind its star, also known as a secondary eclipse (taken in November 2016); and the brightness of WASP-121 b as a function of its phase angle relative to the star (the varying amount of light received on Earth by an exoplanet as it orbits its parent star, similar to the phase cycle of our moon). These data were taken in March 2018 and February 2019 respectively.

“The assembled dataset represents a significant observation time for a single planet and is currently the only consistent set of such repeated observations,” Changeat said. The information we extracted from these observations was used to infer the chemistry, temperature, and cloudiness of WASP-121 b’s atmosphere at different times. This has given us an exquisite picture of how the planet has changed over time. »

Hubble’s unique capabilities are also evident in the wide range of science programs it will enable through its Cycle 31 observations, which began on December 1. About two-thirds of Hubble’s time will be spent on imaging studies, while the rest will be spent on spectroscopy studies. , like those used for WASP-121 b. More details on cycle 31 sciences can be found in a recent announcement.