Recent observations by the James Webb Space Telescope have shed light on the mysterious super-Earth 55 Cancri e, revealing that its atmosphere is likely composed of gases such as carbon monoxide or carbon dioxide. The discovery highlights the extreme conditions of the planet due to its proximity to its star and its potential to provide insights into the early atmospheres of rocky planets.

55 Cancri e is one of five known planets orbiting a sun-like star in the constellation Cancer. With a diameter nearly twice that of Earth and a slightly higher density, the planet is classified as a super-Earth: larger than Earth, smaller than Neptune, and similar in composition to the rocky planets in our solar system.

Brice-Olivier Demory, from the CSH Center for Space and Habitability at the University of Bern and NCCR PlanetS member, co-authored the study. Nature.

He says: “55 Cancri e is one of the most mysterious exoplanets. Despite the enormous amount of observing time gained by a dozen ground-based and space-based instruments over the past decade, its nature remained elusive until the pieces of the puzzle were finally put together thanks to the James Webb Space Telescope (JWST).”

Unexpectedly, these observations show that a hot, highly irradiated rocky planet could support a gaseous atmosphere, demonstrating JWST’s ability to characterize cooler—potentially habitable—rocky planets orbiting Sun-like stars. Renew Hu from NASA’s Jet Propulsion Laboratory (JPL) leads the team that published their findings at: Nature. “JWST really pushes the boundaries of exoplanet characterization toward rocky exoplanets,” Hu said. “It really opens up a new kind of science.”

CHEOPS space telescope achieved important results

While Demory was studying at the Massachusetts Institute of Technology (MIT), he was invited to the research program by Hu, one of his colleagues. Demory has been working on 55 Cancri e since the beginning of his career: “As a research assistant at MIT, I led the discovery of the first flyby of 55 Cancri e, and in 2016 my team published the first map of the rocky exoplanet 55 Cancri e.”

The 2016 results already pointed to the possible existence of an atmosphere around 55 Cancri e. For this study, Demory performed an independent analysis of the JWST dataset. He explains: “Over the last two years, the CHEOPS space telescope, designed and built at the University of Bern, has been instrumental in solving many questions that astrophysicists had about 55 Cancri e. JWST completed this image in the infrared wavelength range, showing that the super-Earth 55 Cancri e is carbon monoxide, or “It showed that it may have been surrounded by an atmosphere with a composition consistent with carbon dioxide.”

A super-hot super-Earth that’s still cooler than expected

Although 55 Cancri e is similar in composition to the rocky planets in our solar system, describing it as “rocky” may give the wrong impression. The planet orbits so close to its star (a full orbit takes 18 hours, compared to Earth’s 365 days) that its surface must be molten; a deep, boiling ocean of magma. With such a narrow orbit, the planet is also likely to be tidally locked; The day side is always facing the star, and the night side is always in darkness. “The planet is so hot that some of the molten rock has to evaporate,” Hu explained.

Although JWST cannot take a direct image of 55 Cancri e, it can measure subtle changes in the light coming from the system as the planet orbits the star. The team used JWST’s NIRCam (Near Infrared Camera) and MIRI (Mid Infrared Instrument) to measure infrared light from the planet. The team was able to calculate the brightness during a secondary eclipse when the planet was behind the star (starlight only) by subtracting the brightness when the planet was near the star (light from the star and planet combined). The amount of infrared light arriving at various wavelengths simultaneously from the dayside of the planet.

The first indication that 55 Cancri might have a significant atmosphere came from temperature measurements based on thermal radiation, or heat energy emitted in the form of infrared light. If the planet is covered in dark molten rock with a thin blanket of vapor rock, or if there is no atmosphere at all, the daytime temperature should be around 2200 degrees Celsius.

“Instead, MIRI data showed a relatively low temperature of about 1,500 degrees Celsius,” Hu said. “This is a very strong indication that energy is distributed from the day side to the night side, most likely through a volatile-rich atmosphere.” Although lava flows can transfer some of the heat to the night side, they cannot move it efficiently enough to account for the cooling effect. In fact, even though the heat is evenly distributed throughout the planet, the dayside appears to be several hundred degrees cooler than it should be. This makes sense if some of the infrared light emitted by the surface is absorbed by the atmosphere and never reaches the telescope.

Bubbling magma ocean

The team believes that the gases covering 55 Cancri e came from the interior. The primary atmosphere was not present for long periods of time due to the star’s high temperature and intense radiation. This would be the secondary atmosphere, constantly replenished by the magma ocean. Magma consists not only of crystals and liquid rocks, but also contains abundant dissolved gases.

Although 55 Cancri e is too hot to be habitable, it could provide a unique window into the interactions between the atmospheres, surfaces, and interiors of rocky planets and provide insights into the early Earth, Venus, and Mars that are thought to be likely covered. by magma oceans of the long past. “Ultimately, we want to understand what conditions allow a rocky planet to maintain a gas-rich atmosphere: the essential ingredient of a habitable planet,” Hu said. said.