Scientists determine alien world's temperature thanks to James Webb's pinpoint precision

"We thought it could have a thick carbon dioxide atmosphere like Venus."

The coolest rocket exoplanet

TRAPPIST-1c is tidally locked, meaning it has one side that constantly faces its host star. In their analysis, the researchers found that the exoplanet's dayside has a temperature of roughly 380 kelvins (225 degrees Fahrenheit, or 107 degrees Celsius). This makes it the coolest rocky exoplanet ever characterized based on thermal emission.

The new study shows off Webb's impressive capability for characterizing rocky exoplanets with similarities to planets in our solar system. It is also an important new step in determining whether planets orbiting small red dwarfs, like TRAPPIST-1 may be able to sustain atmospheres and life. These are the most common type of stars in the Milky Way galaxy, so determining whether they could host life is a key goal in the search for extraterrestrial life.

TRAPPIST-1 b lacked atmosphere. TRAPPIST-1 c? Much the same. Though thought to be similar to Venus (both in size and amounts of radiation from its star), Webb found it lacks Venus’s thick CO2-rich atmosphere. If there is one, it’s very thin. https://t.co/41DctdtCNy pic.twitter.com/fZ0Hh68a99

— NASA Webb Telescope (@NASAWebb) June 19, 2023

The researchers behind the study, who published their findings in a new paper in the journal Nature, claim their research would not have been possible without the capabilities of James Webb.

"We want to know if rocky planets have atmospheres or not," Sebastian Zieba, a graduate student at the Max Planck Institute for Astronomy in Germany and first author of the study explained in the NASA post. "In the past, we could only really study planets with thick, hydrogen-rich atmospheres. With Webb, we can finally start to search for atmospheres dominated by oxygen, nitrogen, and carbon dioxide."

The precision of Webb's MIRI instrument

The team used Webb's Mid-Infrared Instrument (MIRI) to observe the TRAPPIST-1 system on four different occasions. They measured the amount of mid-infrared light emitted by the planet, which allowed them to infer the temperature of the planet.

They measured the brightness of the star by itself when the planet was behind the star and the brightness when the planet was beside the star — allowing them to analyze light from the star and planet combined. By comparing these two measurements, they were able to determine the mid-infrared light coming from the dayside of the planet totaled 15 microns.

According to NASA, the decrease in brightness detected by Webb as the planet moved behind the star was 0.04 percent. This is equivalent to looking at 10,000 tiny light bulbs and noticing that only four have gone out. With such impressive capabilities, Webb will help us unearth the mysteries of countless alien worlds.