The James Webb Space Telescope continues to push the boundaries of our understanding of the universe. Its groundbreaking capabilities extend beyond detecting distant planets; it can also delve into their atmospheres, revealing intricate details about their environments. New research using Webb has unveiled a fascinating phenomenon: differing conditions between the morning and evening sides of a distant exoplanet. This is the first time such variations have been observed on a planet beyond our solar system.
The research focused on WASP-39 b, a gas giant planet situated 700 light-years away. Previously, Webb had studied this planet to gain insights into its atmosphere. WASP-39 b orbits incredibly close to its star, completing a full orbit in a mere four days, resulting in extremely high temperatures. Additionally, it is tidally locked, meaning one side perpetually faces its star while the other is eternally turned away, leading to a stark contrast in conditions between the two hemispheres.
The study delved into the boundary separating the star-facing side, known as the dayside where it’s an eternal morning, and the opposite side, the nightside, experiencing perpetual evening. This boundary, termed the terminator region, was divided into two semicircles representing the morning and evening conditions. “This is the first time that a separate measurement of a direct evening and morning spectrum of an exoplanet has been possible,” stated researcher Maria Steinrück of the University of Chicago in a press release. “This method can greatly help with understanding the climate of exoplanets.”
The data collected revealed a significant temperature difference: the evening side was scorching hot at 1,450 degrees Fahrenheit (800 degrees Celsius), while the morning side was comparatively cooler at 1,150 degrees Fahrenheit (600 degrees Celsius). The researchers attribute the hotter evening temperatures to the presence of clouds that could trap heat, as well as powerful winds, reaching thousands of miles per hour, that carry hot gas from the dayside to the nightside.
This remarkable achievement in measuring such minute temperature differences was only made possible by Webb’s exceptional sensitivity. The telescope’s NIRSpec (Near-Infrared Spectrograph) instrument detected subtle changes in the light emanating from the host star as it passed through the planet’s atmosphere. “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,” commented fellow researcher Néstor Espinoza of the Space Telescope Science Institute. “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.”
