Web Journey to Understand the Strange Atmosphere in a Far Away World

Near-infrared spectroscopy of the terminating star confirms differences in the morning and evening atmosphere.

Since the first exoplanet Thousands of planets orbiting stars outside our solar system were discovered in 1992, and their existence has been confirmed through a myriad of different methods, including direct imaging, gravitational microlensing, transit measurement, and astronomical measurements. Over the years, techniques for studying these exoplanets have evolved, as astronomers learn details about the atmospheric compositions of these distant worlds.

NASA‘s James Webb Space Telescope This field of study continues to develop and deepen our understanding of the diversity of exoplanets and their atmospheres.

What’s new? Webb has allowed astronomers to analyze the atmospheric differences between morning and evening on a tidally locked exoplanet — an incredible feat for a world as distant as WASP-39 b, 700 light-years from Earth.

This artist’s concept shows what the exoplanet WASP-39 b might look like based on indirect transit observations from NASA’s James Webb Space Telescope as well as other space- and ground-based telescopes. Credits: NASA, ESA, CSA, Ralph Crawford (Space Science Institute)

Webb Space Telescope Looks at Eternal Sunrises and Sunsets on Distant Worlds

Researchers using NASA’s James Webb Space Telescope have finally confirmed what models previously predicted: The exoplanet has differences between its eternal morning atmosphere and its eternal evening atmosphere. WASP-39 b, a giant planet 1.3 times larger in diameter than our own. Jupiterbut a block similar to Saturn The planet orbits a star about 700 light-years away from Earth, and is tidally locked to its parent star. This means it has a constant day side and a constant night side – one side of the planet is always exposed to its star, while the other side is always shrouded in darkness.

Using the Webb Observatory’s near-infrared spectrometer, astronomers confirmed a temperature difference between eternal morning and eternal evening on WASP-39 b, with evening appearing about 300 degrees Celsius hotter. F Degrees (about 200 Celsius They also found evidence of different cloud cover, with the perpetual morning part of the planet likely to be cloudier than the evening.

This animation describes how Webb uses transmission spectroscopy to study the atmospheres of distant exoplanets. Image credit: NASA, ESA, CSA, Leah Hostak

Advances in Atmospheric Studies of Exoplanets

Astronomers analyzed a 2- to 5-micron transition spectrum of WASP-39 b, a technique that studies the exoplanet’s tail, the boundary between the day side and the night side of the planet. A transition spectrum is created by comparing starlight filtered through the planet’s atmosphere as it moves in front of the star, with unfiltered starlight detected when the planet is next to the star. By making this comparison, researchers can gain information about the temperature, composition, and other properties of the planet’s atmosphere.

“WASP-39 b has become a benchmark planet for studying exoplanet atmospheres with the Webb telescope,” said Nestor Espinosa, an exoplanet researcher at the Max Planck Institute for Space Sciences. Space Telescope Science Institute “The planet has a puffy atmosphere, so the signal from starlight passing through the planet’s atmosphere is very strong,” says the study’s lead author.

This light curve from NASA’s James Webb Space Telescope shows the brightness of the WASP-39 star system changing over time as the planet transits the star. The observation was made using NIRSpec’s Bright Object Timeline mode, which uses a grid to spread out the light from a single bright object (such as WASP-39 b’s host star) and measure the brightness of each wavelength of light over specific time intervals. Credits: NASA, ESA, CSA, Ralph Crawford (Space Science Institute)

Insights into temperature and atmospheric composition

Previously published Webb spectra of WASP-39b’s atmosphere, which revealed the presence of carbon dioxide, sulfur dioxide, water vapor, and sodium, represented the entire day/night boundary—there was no detailed attempt to distinguish one side from the other.

Now, the new analysis constructs two different spectra from the end zone, splitting the day-night boundary into two halves, one from the evening and the other from the morning. The data reveals that the evening was significantly hotter, at 1,450 degrees Fahrenheit (800 degrees Celsius), and the morning was relatively cooler, at 1,150 degrees Fahrenheit (600 degrees Celsius).

This penetrating spectrum, taken using the Bright Object Time-Sequence mode of the Webb Observatory’s Near-Infrared Spectrograph (PRISM) instrument, shows how much near-infrared starlight is blocked by the atmosphere of the hot gas giant exoplanet WASP-39 b. The spectrum shows clear evidence of water and carbon dioxide, and a temperature difference between morning and evening on the exoplanet.
A new study of the light transmission spectrum of WASP-39 b has shown that there are two distinct spectra of the constant day-night boundary on the exoplanet, dividing this endpoint region into two halves, one from the evening and the other from the morning. The data reveal that the evening was significantly hotter, at 1,450 degrees Fahrenheit (800 degrees Celsius), and the morning was relatively cooler, at 1,150 degrees Fahrenheit (600 degrees Celsius).
The blue and yellow lines represent the best model that takes into account the known data and properties of WASP-39 b and its star (e.g. size, mass, temperature) and the hypothesized properties of the atmosphere.
Copyright: NASA, ESA, CSA, Ralph Crawford (Space Telescope Science Institute)

Effects of temperature changes

“It’s really amazing that we were able to resolve such a small difference, and it’s only possible because of Webb’s sensitivity at near-infrared wavelengths and its very stable optical sensors,” Espinosa said. “Any small movement in the instrument or with the observatory while collecting data would have severely limited our ability to make this detection. It has to be extraordinarily precise, and that’s exactly what Webb is.”

Comprehensive modeling of the data obtained also allows the researchers to investigate the structure of WASP-39 b’s atmosphere, its cloud cover, and why evenings are warmer. While future work by the team will examine how cloud cover might affect temperature, and vice versa, the astronomers have confirmed that the rotation of gas around the planet is the main reason for the temperature differences on WASP-39 b.

Understanding planetary wind patterns and temperature dynamics

On a very radiant exoplanet like WASP-39 b that orbits relatively close to its star, researchers would generally expect gas to move as the planet orbits its star: The hotter gas should move from the day side during the evening to the night side via a strong equatorial jet stream. Because the temperature difference is so great, the atmospheric pressure difference would also be large, which in turn would lead to high wind speeds.

Using general circulation models, three-dimensional models similar to those used to predict weather patterns on Earth, the researchers found that the prevailing winds on WASP-39 b likely move from the night side across the morning endline, around the day side, across the evening endline, and then around the night side. As a result, the morning side of the endline is cooler than the evening side. In other words, the morning side is hit by airflows that have been cooled on the night side, while the evening side is hit by hot airflows on the day side. Research suggests that wind speeds on WASP-39 b could reach thousands of miles per hour!

Future Research Directions and Webb’s Early Scientific Contributions

“This analysis is also particularly interesting because you get 3D information about the planet that you didn’t get before,” Espinosa added. “Because we can tell that the evening edge is hotter, that means it’s a little bit more puffy. So, theoretically, there’s a little bit of a bulge at the end that’s coming toward the night side of the planet.”

The team’s results were published in the journal nature.

Researchers will now seek to use the same analysis method to study the atmospheric variations of other tidally locked hot Jupiters, as part of the Webb 3969 Public Observers Program.

WASP-39 b was among the first targets Webb analyzed when it began regular science operations in 2022. Data in this study were collected under the Early Science Release 1366 program, which is designed to help scientists quickly learn how to use the telescope’s instruments and realize its full scientific potential.

Reference: “Asymmetric Terminators on the Exoplanet WASP-39 b” by Nestor Espinosa, Maria E. Steinrock, James Kirk, Ryan J. McDonald, Arjun P. Saville, Kenneth Arnold, and Eliza M.-R. Kempton, Matthew M. Murphy, Ludmila Carone, Maria Zamyatina, David A. Lewis, Dominic Samra, Sven Kiefer, Emily Rauscher, Duncan Christie, Nathan Mayne, Christiane Helling, Zafar Rustamkulov, Vivien Parmentier, Erin M. May, Aarynn L. Carter, Xi Zhang, Mercedes López-Morales, Natalie Allen, Jasmina Blecic, Leen Decin, Luigi Mancini, Karan Molaverdikhani, Benjamin V. Rackham, Enric Palle, Shang-Min Tsai, Eva-Maria Ahrer, Jacob L. Bean, Ian J.M. Crossfield, David Haegele, Eric Hébrard, Laura Kreidberg, Diana Powell, Aaron D. Schneider, Luis Welbanks, Peter Wheatley, Rafael Brahm and Nicolas Crouzet, July 15, 2024, nature.
DOI: 10.1038/s41586-024-07768-4

The James Webb Space Telescope (JWST) is a large space observatory that was launched on December 25, 2021. It is a collaborative project of NASA, Harvard University, and the University of California, Berkeley. European Space Agency (ESA), and the Canadian Space Agency (CSA). As the scientific successor to the Hubble Space TelescopeThe James Webb Space Telescope is designed to provide unprecedented resolution and sensitivity in the infrared range of the electromagnetic spectrum. This capability allows astronomers to study every stage of cosmic history – from the first flares after the great explosionLocated at the second Lagrange point (L2), the James Webb Telescope will explore a wide range of scientific questions, helping to reveal new insights into the structure and origins of the universe.