James Webb: An exoplanet with hot evenings

Researchers assume that cloud cover is different, with the morning side likely to be cloudier than the evening. Ratings The James Webb Space Telescope observations are published in the current issue of Nature Astronomy. Researchers from the ÖAW Institute for Space Research Graz (IWF) supported the evaluation of the data with their climate and cloud models.

Scientists observed the planets transiting WASP 39b using the space telescope. During these transits, the planet passes in front of its star in a kind of mini-eclipse, and from the telescope's perspective, its light is slightly dimmed. “WASP 39b has become a reference planet in studying exoplanet atmospheres using Webb,” he noted. Nestor Espinosa“It has a puffy, puffy atmosphere, which means that the signal coming from starlight that's filtered through the planet's atmosphere is very strong,” said lead author of the paper and exoplanet researcher at the Space Telescope Science Institute in Baltimore, USA.

Other Chemistry

Immediately before and after total occultation, there is always a partial eclipse, where the right or left hemisphere of the exoplanet is preferably in front of the star. This period, in the thick atmosphere of the morning-afternoon. The evening of WASP 39b is almost “in front of the star”, and was especially interesting for the observers: The atmosphere behind their “fingerprints” in the combined light spectrum of the stars, which is closed to its chemical composition. Now, for the first time, it is possible to use a space telescope to resolve the atmospheric composition separately on the morning and evening sides of an exoplanet.

This revealed clear differences in the chemical composition of WASP 39b: the morning side shows less CO2 than the evening side. According to the Graz researchers, detailed 3D climate cloud models prepared by the IWF suggest that the different CO2 values ​​could come from the cloudier morning side compared to the evening side, which is therefore about 200 °C cooler: this is the situation of 600 °C in the morning and 800 °C in the evening.

dynamic atmosphere

Ludmila Caroni, who belongs to IWF Director Christian Helling’s exoplanet group, predicted “cloud asymmetries” for WASP 39b as early as 2023. “This is of course a great success for us,” said Caroni. “It takes a very long time to build such 3D climate models and then tie them into a full cloud model. But these and other measurements show that the effort was worth it.”

In contrast, chemical models also suggested that the morning side of WASP 39b should be generally cool enough to produce a lot of methane compared to the evening side. However, the data showed that methane was missing from both the evening and morning sides. According to the IMF, one reason could be a highly dynamic atmosphere in which a huge jet of air flows at more than 4,000 kilometers per hour from the hotter evening side to the night side to the morning side and back again, thus suppressing methane production in the region. cooler regions. In addition, vertical mixing with the deeper, hotter layers of the atmosphere could essentially reduce methane production everywhere on the planet. We are still currently investigating the dynamic effect that accounts for how strong it is.

The James Webb Space Telescope collects tiny amounts of infrared light from a distance of 1.5 million kilometers and transmits it to extremely precise measuring instruments. The telescope enables the IMF to understand the climate and weather conditions on exoplanets. The physical interpretation of these observational data requires further development of complex computer models.