Astronomers have detected, for the first time, the atmosphere of a rocky exoplanet outside our solar system using the James Webb Space Telescope (JWST). The atmosphere is rich in carbon dioxide or carbon monoxide. Although this planet may be covered in a magma ocean and unable to support life, studying it can enhance our understanding of early Earth history. The related paper was published on May 8th in "Nature."
An artistic depiction of 55 Cancri e, located close to its star. Image source: Mark Garlick/Science Photo Library
Planet scientist Sara Seager from the Massachusetts Institute of Technology, who was not involved in this study, considers the discovery of atmospheres around Earth-like planets to be a significant milestone in exoplanet research. Earth's thin atmosphere is crucial for sustaining life, and detecting atmospheres on Earth-like planets is an important step in the search for life beyond our solar system.
The planet detected by JWST is named 55 Cancri e. It orbits a Sun-like star located 12.6 light-years away and is considered a super-Earth. Slightly larger than Earth, this Earth-like planet has a radius about twice that of Earth, a mass over 8 times that of Earth, and an atmosphere thickness of a fraction of Earth's radius.
Another reason why 55 Cancri e is not suitable for habitation is its close proximity to its star, about 1/65th the distance from Earth to the Sun. However, astrophysicist and co-author of the paper, Aaron Bello Arufe from NASA's Jet Propulsion Laboratory (JPL), suggests that it may be one of the most studied rocky planets. Being significantly larger than rocky planets in our solar system, it is easier to study compared to other planets outside our solar system.
After thorough study, JWST engineers pointed the observatory's infrared spectrometer at 55 Cancri e for testing following its launch in December 2021. These instruments can detect the chemical fingerprints of gases around planets when they absorb starlight at infrared wavelengths. Bello-Arufe and colleagues then decided to delve deeper to confirm if this planet has an atmosphere.
Prior to recent observations, astronomers had changed their views on 55 Cancri e numerous times. Discovered in 2004, initially, researchers thought it might be the core of a gas giant similar to Jupiter. However, observations with the Spitzer Space Telescope in 2011 as the planet transited its star revealed that 55 Cancri e is actually much smaller than a gas giant, significantly denser, and is a rocky super-Earth.
Years later, researchers noted that the temperature of 55 Cancri e was lower than expected for a planet so close to its star, indicating the possibility of an atmosphere. One hypothesis was that the planet was a "water world" surrounded by supercritical water molecules, while another suggested it was enveloped by an expanded primitive atmosphere mainly composed of hydrogen and helium. However, these ideas were eventually overturned.
JPL planetary scientist and co-author of the paper, Renyu Hu, mentioned that a planet so close to its star would be bombarded by stellar winds, making it difficult to capture volatile molecules in the atmosphere. This presents two possibilities: either the planet is completely dry with an ultra-thin atmosphere composed of evaporated rocks, or it has a thick atmosphere made up of heavier volatile molecules that are not easily lost.
Recent data indicates that the atmosphere of 55 Cancri e contains carbon-based gases, pointing towards the latter possibility. Seager mentioned that the team has gathered real evidence of the atmosphere but further observations are needed to determine its complete composition, the relative abundance of gases, and its precise thickness.
Planetary geologist Laura Schaefer from Stanford University is interested in understanding how the atmosphere of 55 Cancri e interacts with the materials beneath the planet's surface. She mentioned that the atmosphere could still be eroded by stellar winds, but the melting and release of rocks in a magma ocean could replenish gases.
"Earth likely went through at least one magma-ocean phase, perhaps several," Schaefer said. "Having actual examples of magma oceans can help us understand the early history of the solar system."
For more information, refer to the related paper: https://doi.org/10.1038/s41586-024-07432-x
