Researchers using NASA’s James Webb Space Telescope have glimpsed tantalizing new details about what it’s like at the boundary of a tidally locked planet—that is, one where half of the planet is always exposed to its star, while the other is always shrouded in darkness.
A group of scientists, including several from the University of Chicago, studied a giant planet known as WASP-39 b that orbits a star about 700 light-years away from Earth. This planet doesn’t spin constantly like Earth does; one half of the planet experiences a constant daytime and the other is in constant nighttime.
The powerful telescope allowed the scientists to get the most detailed look yet at the conditions in the thin twilight boundary where the day side and night side meet. They were able to discern a temperature difference even within this narrow boundary; half of the boundary zone is significantly hotter than the other half.
This temperature difference is evidence for powerful winds that sweep across the boundary at thousands of miles per hour. The researchers were also able to detect a surprising difference in cloud cover between the regions.
“It’s really stunning that we are able to parse this small difference out, and it’s only possible due to Webb’s sensitivity across near-infrared wavelengths and its extremely stable photometric sensors,” said Néstor Espinoza, an exoplanet researcher at the Space Telescope Science Institute and lead author on the study.
“This is a whole new level of detail,” said co-author Maria Steinrueck, previously with the Max Planck Institute, now a 51 Pegasi b Fellow with the University of Chicago. “Previously, we could only get averages of both planet sides. But there could be so much variation in this small region—temperature, clouds, and atmospheric composition—and we can learn so much more by being able to measure the difference.”
—Prof. Jacqueline Stewart
