Space telescope finds signs of atmosphere around Earth-like exoplanet

The planet was previously speculated to lack atmosphere, but new observations from the James Webb Space Telescope have enabled researchers to study the atmosphere around the Earth-like rocky planet.   

Artwork Credit: NASA, ESA, CSA, Dani Player (STScI)

“On exoplanets, planets outside our solar system, we can study how atmospheres behave under different conditions than those we have on Earth or even in our solar system,” says Alexis Brandeker, Associate Professor at the Department of Astronomy at Stockholm University and co-author of the study. 

40 light years away from our own solar system lies the exoplanet 55 Cancri e. It orbits 65 times closer to its star than the Earth orbits the Sun, resulting in a year lasting only 17 hours. With its proximity to the star, the daytime temperature becomes so high that the surface melts, probably forming a giant ocean of lava. The atmosphere around planets orbiting close to their star is strongly influenced by stellar winds, a flow of gas from a star's upper atmosphere. Therefore, it has been speculated that the atmosphere around 55 Cancri e might have been completely eroded, leaving the planet atmosphere-less. But now, new observations with the James Webb Telescope show that the planet probably has an atmosphere dominated by carbon dioxide or carbon monoxide.

Re-formation of the atmosphere

“The existence of an atmosphere shows that it must be actively re-forming, perhaps through active volcanism driven by the planet's proximity to the star. Without re-formation, models show that the atmosphere would not survive for very long,” says Alexis Brandeker.

Studying the atmosphere of 55 Cancri e is challenging even for the James Webb Telescope. The planet cannot be seen directly, but using the telescope, scientists have examined the infrared light coming from the part of the planet facing its star. They did this by observing an event called occultation, which occurs when the planet passes behind the star. By comparing the difference in light between when the planet is behind the star and when it is right next to it, it is possible to work out how much of the light is coming from the planet.  

The international research team, led by Renyu Hu at the Jet Propulsion Laboratory at CalTech, used new methods to optimally analyze data from the James Webb Telescope. One of the methods was developed in Stockholm by co-authors Alexis Brandeker and Jayshil Patel, a PhD student at the Department of Astronomy. 

Unexpectedly active atmosphere

In parallel with the observing program, James Webb observations of the same planet were also carried out by a sister program at Stockholm University. The aim of that program is to study how the atmosphere around 55 Cancri e varies over time by observing four occultations spread over six months.

“The observations show that the atmosphere around 55 Cancri e is unexpectedly active, with incredible variability that is difficult to explain. If it is due to weather, it is more extreme than we have seen anywhere in the universe,” says Alexis Brandeker. 

The sister study, led by Alexis Brandeker and Jayshil Patel, has been submitted for review but is not yet published.

“A better understanding of how atmospheres behave on exoplanets gives us more robust models of climate evolution and the type of planets we can expect atmospheres to form on. This also has astrobiological implications, as the study of atmospheres is a way to search for life over astronomical distances,” concludes Alexis Brandeker.

Read the study in Nature: A Secondary Atmosphere on the Rocky Exoplanet 55 Cnc e