The data revealed evidence of large quantities of water vapor, methane, and even, for the first time, carbon dioxide in the atmosphere of WASP-39b. A minor sensation, but there is still one fly in the ointment: researchers have not yet succeeded in reproducing all the crucial details of the observations in model calculations. This stands in the way of an even more precise analysis of the data.

In the new study led by the MPS, the authors, including researchers from the Massachusetts Institute of Technology (U.S.), the Space Telescope Science Institute (U.S.), Keele University (United Kingdom), and the University of Heidelberg (Germany), show a way to overcome this obstacle.

"The problems arising when interpreting the data from WASP-39b are well known from many other exoplanets—regardless whether they are observed with Kepler, TESS, James Webb, or the future PLATO spacecraft," explains MPS scientist Dr. Nadiia Kostogryz, first author of the new study. "As with other stars orbited by exoplanets, the observed light curve of WASP-39 is flatter than previous models can explain."

Researchers define a light curve as a measurement of the brightness of a star over a longer period of time. The brightness of a star fluctuates constantly, for example, because its luminosity is subject to natural fluctuations. Exoplanets can also leave traces in the light curve. If an exoplanet passes in front of its star as seen by an observer, it dims the starlight.