Webb’s Journey To Understand a Distant World’s Bizarre Atmosphere

Terminator’s near-infrared spectroscopy confirmed differences in the atmosphere between morning and evening.

From the beginning Exoplanets Since their discovery in 1992, thousands of planets have been confirmed orbiting stars outside our solar system through a variety of methods, including direct imaging, gravitational microlensing, transit measurements, and astronomical measurements. Over the years, techniques for studying these exoplanets have evolved, and astronomers have learned more about the composition of the atmospheres of these far-flung worlds.

National Aeronautics and Space Administration (NASA)of James Webb Space Telescope We continue to further develop this field of research and improve our understanding of exoplanets and the diversity of their atmospheres.

The latest result? Thanks to Webb, astronomers were able to analyze the differences in the morning and evening atmospheres of a tidally locked exoplanet — a remarkable feat for a distant world like WASP-39 b, located 700 light-years from Earth.

This artist’s concept shows what exoplanet WASP-39 b might look like, based on indirect transit observations by NASA’s James Webb Space Telescope and other space- and ground-based telescopes. Credit: NASA, ESA, CSA, Ralph Crawford (STScI)

Webb Space Telescope studies eternal sunrises and sunsets on distant world

Using NASA’s James Webb Space Telescope, researchers have finally confirmed what models have predicted all along: exoplanets have different atmospheres in the morning and night of their stars. WASP-39b, a giant planet 1.3 times the diameter of the Sun, Jupiterbut with similar mass Saturn It orbits a star about 700 light-years from Earth and is tidally locked to its parent star, meaning there is always a day side and a night side of the star, with one side of the planet always exposed to the star and the other always in darkness.

Using Webb’s NIRSpec instrument, astronomers have determined that there is a temperature difference between WASP-39b’s eternal morning and eternal night, with evenings appearing roughly 300 degrees hotter. Fahrenheit degrees (approx. 200 Celsius They also found evidence of differences in cloud cover, with morning parts of the planet likely to be much cloudier than evening parts.

This animation explains how Webb uses transmission spectroscopy to study the atmospheres of distant exoplanets. Credit: NASA, ESA, CSA, Leah Hastak

Advances in research into exoplanet atmospheres

Astronomers analyzed WASP-39 b’s 2-5 micron transmission spectrum, a technique for studying exoplanet boundaries — the boundaries that separate a planet’s dayside from its nightside. A transmission spectrum is created by comparing the starlight that passes through the planet’s atmosphere as it moves in front of it with the starlight that isn’t transmitted when the planet is next to the star. This comparison allows researchers to learn information about the temperature, composition, and other properties of the planet’s atmosphere.

“WASP-39 b has become something of a benchmark planet for Webb’s research into exoplanet atmospheres,” he said. Space Telescope Science Institute “Because the planet’s atmosphere is inflated and fluffy, the signal from the starlight filtered through the planet’s atmosphere is very strong,” said the study’s lead author.

A light curve from NIRSpec (Near-Infrared Spectrograph) on NASA’s James Webb Space Telescope shows how the brightness of the WASP-39 star system changes over time as a planet passes by the star. The observations were made using NIRSpec’s Bright Object Time Series mode, which uses a grating to scatter the light from a single bright object (such as WASP-39 b’s host star) and measure the brightness of each wavelength of light at set time intervals. Credit: NASA, ESA, CSA, Ralf Crawford (STScI)

Insights into temperature and atmospheric composition

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).

This transmission spectrum, taken with Webb’s NIRSpec (Near-Infrared Spectrometer) PRISM in its Bright Object Time Series mode, shows the amount of near-infrared starlight blocked by the atmosphere of hot, gas-giant exoplanet WASP-39 b. The spectrum shows clear evidence of water and carbon dioxide on the exoplanet, as well as changes in temperature between morning and evening.
A new analysis of WASP-39 b’s transmission spectrum constructed two different spectra from the exoplanet’s stationary day-night boundary, essentially splitting this boundary region into two semicircles, one from the evening and one from the morning. The data revealed that the evenings were quite hot, at a scorching 1,450 degrees Fahrenheit (800 degrees Celsius), while the mornings were a relatively cool 1,150 degrees Fahrenheit (600 degrees Celsius).
The blue and yellow lines are the best-fit models that take into account the data, the known properties of WASP-39 b and its star (such as size, mass, and temperature), and the expected properties of its atmosphere.
Credits: NASA, ESA, CSA, Ralf Crawford (STScI)

Effects of temperature changes

“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.

Understanding planetary wind patterns and temperature dynamics

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.

Future research directions and Webb’s early scientific contributions

“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 findings were published in the journal Nature.

The researchers plan to use the same analysis to study differences in the atmospheres of other tidally locked hot Jupiters in the future as part of the Webb Cycle 2 General Observation Program 3969.

WASP-39 b was one of the first targets analyzed when Webb begins regular science observations in 2022. Data for this study were collected under Early Release Science Program 1366, designed to help scientists quickly learn how to use the telescope’s instruments and realize its full scientific potential.

Reference: “Nonuniform boundary conditions on the exoplanet WASP-39 b” by Néstor Espinoza, Maria E. Steinrueck, James Kirk, Ryan J. MacDonald, Arjun B. Savel, Kenneth Arnold, Eliza M.-R. Kempton, Matthew M. Murphy, Ludmila Carone, Maria Zamyatina, David A. Lewis, Dominik Samra, Sven Kiefer, Emily Rauscher, Duncan Christie, Nathan Main, Christiane Herring, Zafar Rustamkulov, Vivian Parmentier, Erin M. May, Arlyn L. Carter, Xi Zhang, Mercedes Lopez-Morales, Natalie Allen, Jasmina Bresic, Leanne Dessin, Luigi Mancini, Karan Moraverdicani, Benjamin V. Rackham, Enric Paré, Shanmin Tsai, Eva Maria Erler, Jacob L. Bean, Ian J.M. Crossfield, David Hagel, Eric Hebrard, Laura Kreidberg, Diana Powell, Aaron D. Schneider, Lewis Wellbanks, Peter Wheatley, Raphaël Brahm, Nicolas Crozet, July 15, 2024, Nature.
DOI: 10.1038/s41586-024-07768-4

The James Webb Space Telescope (JWST) is a large space observatory launched on December 25, 2021. It is a NASA, European Space Agency (ESA), as the scientific successor to the Canadian Space Agency (CSA); Hubble Space TelescopeJWST is designed to provide unprecedented resolution and sensitivity in the infrared region of the electromagnetic spectrum, a capability that will enable astronomers to study every stage of the history of the Universe. big bangthe formation of a solar system capable of supporting life on an Earth-like planet, and the evolution of our own solar system, JWST will explore a range of scientific questions and help discover new insights into the structure and origins of the universe.