The new space telescope once again shows what’s inside the gas giant Wasp-39b. And the next tasks are already waiting.
This illustration shows what the planet Wasp-39b might look like. In the background the mother star.
The James Webb Telescope keeps researchers on their toes. Just a few days ago, Nasa and ESA published a detailed infrared image of Jupiter. Now there is already the next success message. An international team with Swiss participation has used the space telescope to detect carbon dioxide in the atmosphere of an extrasolar planet for the first time. The observation provides clues as to where the planet formed. Above all, it makes you want more.
No comparable planet in the solar system
The object of investigation is the gas planet Wasp-39b. It is similar in mass to Saturn and orbits a Sun-like star 700 light-years from us. One searches in vain for anything comparable in our solar system. The gas planet orbits its parent star in such a narrow orbit that one orbit takes only four days. It is correspondingly hot on its surface. The side facing the star heats up to 900 degrees Celsius. So the planet is literally grilled.
As seen from Earth, Wasp-39b keeps crossing line of sight to its parent star, momentarily eclipsing it. This is how the planet was discovered in 2011. But the light of the mother star reveals even more. During a transit, part of the light passes through the planet’s atmosphere and is partially absorbed there. If the light is broken down into its spectral components, the absorption lines can be used to determine which gases are in the atmosphere. In this way, water vapor was detected in the atmosphere of Wasp-39b in 2018, and later also sodium and potassium.
This made Wasp-39b a candidate for the James Webb telescope. Many gases primarily absorb infrared radiation. This is exactly the wavelength range in which the space telescope operates. It should therefore be possible to detect gases that optical telescopes cannot see, or at least not very well.
Wasp-39b is among the first extrasolar planets to be studied with the James Webb Telescope as part of the Early Release Science program. The planet is extreme, says Monika Lendl from the University of Geneva, who was involved in the study. That’s what makes him so interesting.
The increased absorption of light at a wavelength of 4.2 microns tells researchers that Wasp-39b’s atmosphere must contain carbon dioxide.
Using the James Webb telescope’s near-infrared spectrograph, the researchers were able to detect the fingerprint of carbon dioxide. According to Lendl, it is the first time that this greenhouse gas has been unequivocally detected in the atmosphere of an extrasolar planet. The Spitzer space telescope has already provided clues. This time, however, the evidence is clear.
The measured spectrum fits very well with a model of the planetary atmosphere. The model suggests that in addition to carbon dioxide, carbon monoxide and hydrogen sulfide should also be present in the atmosphere. Measurements with other instruments of the James Webb telescope, which are currently being evaluated, could provide confirmation of this. These measurements could also provide an explanation for a small discrepancy. An absorption line appears in the spectrum that the model does not reproduce. So there must be a gas in the atmosphere that is missing in the model, says Lendl.
From the measurements so far, it can be deduced that the gas giant can hardly have formed where it is circling today. Its atmosphere contains too many heavy elements like carbon for that. These are scarce in the inner regions of the disk where planets are forming. So Wasp-39b must have originated further out and then migrated inwards.
For Lendl, however, another aspect is in the foreground: the first observations of Wasp-39b exceeded all expectations. One could not wish for better conditions to examine the thinner atmosphere of Earth-like rocky planets with the James Webb telescope in the future.
Follow the science editors of the NZZ Twitter.