Researchers using NASA’s James Webb Space Telescope have finally confirmed what models have predicted all along: exoplanets have a difference between their permanent morning atmosphere and their permanent night atmosphere. WASP-39 b is a giant planet with a diameter 1.3 times that of Jupiter and a mass similar to Saturn, orbiting a star about 700 light-years from Earth and is tidally locked to its parent star. This means that it has a permanent dayside and a permanent nightside, with one side of the planet always exposed to the star and the other always in darkness.
Using Webb’s NIRSpec instrument, the astronomers confirmed that there is a temperature difference between WASP-39 b’s eternal morning and eternal evening, with the evening appearing to be roughly 300 degrees Fahrenheit (about 200 degrees Celsius) hotter. They also found evidence of different cloud cover, suggesting that the eternal morning parts of the planet are likely cloudier than the evenings.
Astronomers have discovered particles between 2 and 5 microns Transmission spectrum WASP-39 b’s technique will study the boundary, the boundary between the dayside and nightside of an exoplanet. A transmission spectrum is created by comparing the star’s light that is transmitted through the planet’s atmosphere as it moves in front of it with the untransmitted starlight detected when the planet is next to the star. Making this comparison gives researchers information about the temperature, composition and other properties of the planet’s atmosphere.
“WASP-39 b serves as a kind of benchmark planet for the Webb mission’s exoplanet atmospheric studies,” said Nestor Espinosa, an exoplanet researcher at the Space Telescope Science Institute and lead author of the study. “The planet’s atmosphere is puffy and fluffy, so the signal from the star’s light passing through the planet’s atmosphere is very strong.”
A web spectrum of the atmosphere of WASP-39b was previously published, Carbon dioxide, sulfur dioxide, water vapor, sodiumrepresents the entire boundary between day and night, with no detailed attempt to distinguish one from the other.
Now, in a new analysis, they created two different spectra from the boundary region, splitting the day/night boundary into two semicircles: one taken from the evening and one from the morning. The data shows that the evening was significantly hotter, reaching a scorching 1,450 degrees Fahrenheit (800 degrees Celsius), while the morning was a relatively cool 1,150 degrees Fahrenheit (600 degrees Celsius).
“It’s really amazing that we were able to resolve this small difference, and it’s thanks to Webb’s sensitivity to near-infrared wavelengths and its extremely stable photometric sensor,” Espinoza said. “Any movement of the instrument or the observatory while collecting the data would severely limit our ability to detect this. This requires extraordinary precision, and Webb is exactly that.”
Extensive modeling of the resulting data will also allow the researchers to investigate the structure of WASP-39 b’s atmosphere, its cloud cover, and why it’s hotter in the evenings. The team will next investigate how cloud cover affects temperature and vice versa, but the astronomers confirmed that the circulation of gas around the planet is the main cause of WASP-39 b’s temperature difference.
For highly irradiated exoplanets that orbit relatively close to their stars, like WASP-39 b, researchers typically expect gas to move as the planet rotates around its star. This means that hotter gas on the dayside should be transported from the evening to the nightside by the strong equatorial jet stream. The extreme temperature difference would lead to large pressure differences, which would result in faster wind speeds.
Using the General Circulation Model, a three-dimensional model similar to those used to predict weather patterns on Earth, the researchers found that on WASP-39 b, prevailing winds tend to move from the night side across the morning boundary, around the day side, across the evening boundary, and back around the night side. As a result, the morning side of the boundary is cooler than the evening side. In other words, the morning side is hit by winds of air cooled by the night side, and the evening side is hit by winds of air heated by the day side. Wind speeds on WASP-39 b can reach thousands of miles per hour, according to the study.
“This analysis is particularly interesting because it gives us previously unavailable 3D information about the planet,” Espinoza added. “The fact that the evening edge is hotter means that it’s bulging out a bit, which means that in theory there’s a little undulation at the boundary approaching the planet’s night side.”
The team’s achievements Nature.
The researchers aim to use the same analytical method to study differences in the atmospheres of other tidally locked planets. Hot Jupiteras part of Webb Cycle 2 Public Observation Program 3969.
WASP-39 b was one of the first targets analyzed when Webb begins its regular science observations in 2022. The data for this study were collected under the Early Release Science Program. 1366It is designed to help scientists quickly learn how to use the telescope’s instruments and maximize its scientific potential.
The James Webb Space Telescope is the world’s premier space science observatory. The Webb Telescope is unlocking the mysteries of our solar system, observing distant worlds around other stars, and probing the mysterious structure and origin of the universe and our place in it. The Webb Telescope is an international program conducted by NASA with partners ESA (European Space Agency) and CSA (Canadian Space Agency).
