Researchers using James Webb to probe eternal sunrises and sunsets on distant world

An exoplanet has differences between its eternal morning and eternal evening atmosphere - this model was previously predicted and researchers have finally confirmed it using the James Webb Space Telescope.

Researchers are talking about WASP-39 b, which is a gas giant exoplanet that orbits a G-type star. The mass WASP-39 b is 0.28 Jupiter and it takes 4.1 days to complete one orbit of its star, NASA revealed. WASP-39 b has a similar mass to Saturn. It orbits a star about 700 light-years away from Earth.

The discovery of WASP-39 b was announced in 2011 and in July 2022, it became the first exoplanet to be studied by NASA's James Webb Space Telescope, which is the largest, most powerful telescope ever launched into space.

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Researchers have established that WASP-39 b is tidally locked to its parent star, which means it has a constant dayside and a constant nightside. One side of the planet is always exposed to its star, while the other is always covered in darkness.

NASA in its reports said that astronomers confirmed a temperature difference between the eternal morning and eternal evening on WASP-39 b using Webb's NIRSpec (Near-Infrared Spectrograph).

The astronomers found that evening appeared hotter by about 200 degrees Celsius and there is evidence for different cloud cover, with the "forever morning portion of the planet being likely cloudier than the evening".

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As quoted by nasa.gov, Néstor Espinoza, who is an exoplanet researcher at the Space Telescope Science Institute and lead author on the study, said,"WASP-39 b has become a sort of benchmark planet in studying the atmosphere of exoplanets with Webb."

"It has an inflated, puffy atmosphere, so the signal coming from starlight filtered through the planet’s atmosphere is quite strong," Espinoza added.

The complete day/night boundary is represented by the previously published Webb spectra of the atmosphere of WASP-39b, which showed the presence of carbon dioxide, sulphur dioxide, water vapour and sodium. But there was no detailed attempt to differentiate between one side and the other.

However, the day/night boundary is now divided into two semicircles, one from the evening and one from the morning, by the new methodology, which constructs two distinct spectra from the terminator region.

"Data reveals the evening as significantly hotter, a searing 1,450 degrees Fahrenheit (800 degrees Celsius), and the morning a relatively cooler 1,150 degrees Fahrenheit (600 degrees Celsius)," NASA said in its report.

"It's really stunning that we are able to parse this small difference out, and it’s only possible due Webb's sensitivity across near-infrared wavelengths and its extremely stable photometric sensors," said Espinoza.

"Any tiny movement in the instrument or with the observatory while collecting data would have severely limited our ability to make this detection. It must be extraordinarily precise, and Webb is just that," he added.

The findings were published on Monday (Jul 15) in Nature, titled, "Inhomogeneous terminators on the exoplanet WASP-39 b".

(With inputs from agencies)