A team of international researchers has utilized NASA’s James Webb Space Telescope to determine the level of heat energy emitted by the rocky exoplanet TRAPPIST-1 c. The findings suggest that, if it exists, the planet’s atmosphere is extremely thin.
TRAPPIST-1 c, with a dayside temperature of approximately 380 kelvins (around 225 degrees Fahrenheit), is now recognized as the coolest rocky exoplanet ever characterized based on thermal emission. The precision required for these measurements underscores the significance of Webb’s capabilities in studying rocky exoplanets similar in size and temperature to those within our own solar system.
This outcome represents another advancement in determining whether planets orbiting small red dwarfs like TRAPPIST-1—the most common type of star in the galaxy—can maintain atmospheres capable of supporting life as we know it.
“We aim to ascertain whether rocky planets possess atmospheres or not,” stated Sebastian Zieba, a graduate student at the Max Planck Institute for Astronomy in Germany and the primary author of the published results in Nature. “In the past, our studies were primarily limited to planets with dense atmospheres rich in hydrogen. With Webb, we can finally begin the search for atmospheres dominated by oxygen, nitrogen, and carbon dioxide.”
TRAPPIST-1 c is one of seven rocky planets orbiting an ultracool red dwarf star, situated 40 light-years away from Earth. Although these planets resemble the inner rocky planets in our solar system in terms of size and mass, it remains uncertain whether they possess similar atmospheres. During their initial billion years, M dwarfs emit intense X-ray and ultraviolet radiation capable of stripping away the atmosphere of a young planet. Additionally, there may not have been an ample supply of water, carbon dioxide, and other volatile substances during the planet’s formation to create substantial atmospheres.
To address these inquiries, the team employed Webb’s Mid-Infrared Instrument (MIRI) to observe the TRAPPIST-1 system on four separate occasions as the planet moved behind its star, an event known as a secondary eclipse. By comparing the brightness during the planet’s passage behind the star (relying solely on starlight) with the brightness when the planet is beside the star (combining starlight and planet light), the researchers calculated the quantity of mid-infrared light with 15-micron wavelengths emitted by the planet’s dayside.
This method mirrors that of another research team, which determined that TRAPPIST-1 b, the innermost planet in the system, is likely devoid of any atmosphere.