Monday, July 15, 2024

NASA's Webb Investigates Eternal Sunrises, Sunsets On Distant World

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Near-infrared spectral analysis of terminator confirms differences in morning and evening atmosphere

Researchers using NASA's James Webb Space Telescope have finally confirmed what models have previously predicted: An exoplanet has differences between its eternal morning and eternal evening atmosphere. WASP-39 b, a giant planet with a diameter 1.3 times greater than Jupiter, but similar mass to Saturn that orbits a star about 700 light-years away from Earth, is tidally locked to its parent star. This 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 shrouded in darkness.

Using Webb's NIRSpec (Near-Infrared Spectrograph), astronomers confirmed a temperature difference between the eternal morning and eternal evening on WASP-39 b, with the evening appearing hotter by roughly 300 Fahrenheit degrees (about 200 Celsius degrees). They also found evidence for different cloud cover, with the forever morning portion of the planet being likely cloudier than the evening.

Astronomers analyzed the 2- to 5-micron transmission spectrum of WASP-39 b, a technique that studies the exoplanet's terminator, the boundary that separates the planet's dayside and nightside. A transmission spectrum is made by comparing starlight filtered through a planet's atmosphere as it moves in front of the star, to the unfiltered starlight detected when the planet is beside the star. When making that comparison, researchers can get information about the temperature, composition, and other properties of the planet's atmosphere.

Previously published Webb spectra of WASP-39b's atmosphere, which revealed the presence of carbon dioxide, sulfur dioxide, water vapor, and sodium , represent the entire day/night boundary – there was no detailed attempt to differentiate between one side and the other.

"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."

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