May 19, 2024

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Weather web maps on the exoplanet WASP-43b

Weather web maps on the exoplanet WASP-43b

This artist's concept shows what the hot gas giant exoplanet WASP-43 b could look like. WASP-43 b is a Jupiter-sized planet orbiting a star about 280 light-years away, in the constellation Sexta. The planet orbits at a distance of about 1.3 million miles (0.014 astronomical unit, or AU), completing one orbit in about 19.5 hours. Because it is so close to its star, WASP-43 b is likely tidally locked: its rotation rate and orbital period are the same, with one side facing the star at all times. Image credit: NASA, ESA, CSA, Ralph Crawford (STScI)

WASP-43 b is cloudy at night and clear during the day, with tropical winds swirling around the planet at 5,000 miles per hour.

sometimes no Finding something is just as exciting and rewarding as finding it. Take hot Jupiter WASP-43B, for example. This tidally locked world has a perpetually very hot day side and a somewhat cooler night side. Astronomers using Webb to map the temperature and analyze the atmosphere around the planet expect to detect methane, a common carbon molecule, on the night side. But there is clearly no indication of this. Why? The result suggests that supersonic winds of hot gas blow from the dayside, completely turning the atmosphere around, and preventing chemical reactions that would produce methane on the nightside.

The gas giant exoplanet WASP-43 b (Webb MIRI phase curve)

This light curve shows the change in brightness of the WASP-43 system over time as the planet orbits the star. This type of light curve is known as a phase curve because it includes the entire orbit, or all phases of the planet.
Because it is tidally locked, different sides of WASP-43 b rotate as it rotates. The system appears brightest when the hot daytime side faces the telescope, just before and after a secondary eclipse when the planet passes behind the star. The system grows fainter as the planet continues its orbits and its night side orbits the horizon. After the transit, when the planet passes in front of the star, blocking some of the starlight, the system lights up again as the day side rotates back into view.
Image credit: NASA, ESA, CSA, Ralph Crawford (STScI), Taylor Bell (BAERI), Joanna Barstow (The Open University), Michael Roman (University of Leicester)

The Webb Space Telescope maps the weather on a planet 280 light-years away

It has been used successfully by an international team of researchers NASA's James Webb Space Telescope To map the weather on the hot gas giant exoplanet WASP-43 b.

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Precise, large-scale brightness measurements of mid-infrared light, combined with 3-D climate models and previous observations from other telescopes, indicate thick, high clouds covering the night side, clear skies on the day side, and tropical winds more than 5,000 miles high. per hour mixing of atmospheric gases around the planet.

The investigation is just the latest evidence Exoplanet Science is now possible thanks to Webb's extraordinary ability to measure temperature changes and detect atmospheric gases trillions of miles away.

“Hot Jupiter” is tidally locked

WASP-43 b is a type of “hot Jupiter” exoplanet: similar in size to Jupiter, composed primarily of hydrogen and helium, and much hotter than any of the giant planets in our solar system. Although its star is smaller and cooler than the Sun, WASP-43 b orbits at a distance of only 1.3 million miles, less than 1/25 the distance between Mercury and the Sun.

With such a tight orbit, the planet is tidally locked, with one side constantly illuminated and the other in perpetual darkness. Although the night side never receives any direct radiation from the star, strong easterly winds transport heat from the day side.

Since its discovery in 2011, WASP-43 b has been observed using several telescopes, including NASA's Hubble Telescope and the now-retired Spitzer Space Telescopes.

“With Hubble, we can clearly see that there is water vapor on the dayside. Both Hubble and Spitzer have shown that there may be clouds on the nightside,” explained Taylor Bell, a researcher from the Bay Area Environmental Research Institute and lead author of a study published April 30 in Nature astronomy. “But we needed more precise measurements from Webb to actually start mapping more detailed temperature, cloud cover, winds and atmospheric composition all the way around the planet.”

Diagram of an exoplanet's phase curve

This simplified diagram of the exoplanet phase curve shows the change in overall brightness of the star-planet system as the planet orbits the star. The system appears brightest when the illuminated portion of the planet is facing the telescope (full phase). It appears dim when most of the dark side faces the telescope (new phase), when the planet blocks some of the starlight (transit), and when the star blocks the planet's light (secondary eclipse).
(Top) A diagram showing the change in the planet's phase (the amount of illuminated side facing the telescope) as it orbits its star.
(Bottom) A 3-D graph showing the change in overall brightness of the star system and the planet as the planet orbits its star. In this graph, known as the light curve, the horizontal plane is the orbital position and the vertical axis is the brightness.
(Right) Scale bar. In both the orbital diagram and the light curve, color indicates the observed brightness of the star + planet: from dark purple (less light is detected) to white (more light is detected).
Researchers use phase curves to study changes in reflectance and temperature of the planet with longitude (from side to side), which can provide insight into the surface composition and atmospheric conditions of the planet.
Image credit: NASA, ESA, CSA, Danny Player (STScI), Andy James (STScI), Greg Bacon (STScI)

Temperature mapping and weather inference

Although WASP-43 b is too small, dim and close to its star for a telescope to see directly, its short orbit period of just 19.5 hours makes it ideal for phase curve spectroscopy, a technique that involves measuring small changes in a star's brightness. Star and Planet System As the planet orbits the star.

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Since the amount of mid-infrared light emitted by an object depends largely on how hot it is, the brightness data captured by Webb can then be used to calculate the planet's temperature.

The team used Webb's MIRI (mid-infrared instrument) instrument to measure the light from the WASP-43 system every 10 seconds for more than 24 hours. “By observing an entire orbit, we were able to calculate the temperature of the different sides of the planet as they orbited the horizon,” Bell explained. “From that, we can build a rough map of temperature across the planet.”

Measurements show that the average temperature on the day side is about 2,300 degrees F (1,250 degrees Celsius) – hot enough to form iron. Meanwhile, the night side is noticeably cooler at 1,100°F (600°C). The data also helps determine the location of the planet's hottest point (the “hot spot”), which is shifted slightly eastward from the point that receives the most stellar radiation, where the star is highest in the planet's sky. This shift is caused by supersonic winds, which move hot air eastward.

“The fact that we can map the temperature in this way is a real testament to Webb's sensitivity and stability,” said co-author Michael Roman from the University of Leicester in the UK.

To interpret the map, the team used complex 3D atmospheric models like those used to understand weather and climate on Earth. The analysis shows that the night side may be covered by a thick, high layer of clouds that prevents some infrared light from escaping into space. As a result, the night side – although very hot – appears darker and cooler than it would if there were no clouds.

The gas giant exoplanet WASP-43 b (temperature maps)

This set of maps shows the temperature of the visible side of the hot gas giant exoplanet WASP-43 b, as the planet orbits its star. The temperatures were calculated based on more than 8,000 brightness measurements of 5- to 12-micron mid-infrared light detected from the star system and the planet by MIRI (Mid-Infrared Instrument) on NASA's James Webb Space Telescope. In general, the hotter an object is, the more mid-infrared light it emits. Image credit: NASA, ESA, CSA, Ralph Crawford (STScI), Taylor Bell (BAERI), Joanna Barstow (The Open University), Michael Roman (University of Leicester)

Methane loss and high winds

The broad spectrum of mid-infrared light captured by Webb also made it possible to measure the amount of water vapor (H2O) and methane (CH4) around the planet. “Webb has given us an opportunity to know exactly what molecules we see and put some constraints on their abundance,” said co-author Joanna Barstow from the Open University in the UK.

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The spectra show clear signs of water vapor on the night side as well as the day side of the planet, providing additional information about how dense the clouds are and how high they rise in the atmosphere.

Surprisingly, the data also shows a clear difference loss Methane anywhere in the atmosphere. Although the dayside is too hot for methane to exist (most of the carbon must be in the form of carbon monoxide), methane should be stable and detectable on the cooler nightside.

“The fact that we don't see methane tells us that WASP-43 b must have wind speeds of nearly 5,000 miles per hour,” Barstow explained. “If winds moved the gas from the dayside to the nightside and then back again quickly enough, there would not be enough time for the expected chemical reactions to produce detectable amounts of methane on the nightside.”

The team believes that because of this wind-driven mixing, the chemistry of the atmosphere is the same throughout the planet, which was not clear from previous work with Hubble and Spitzer.

Reference: “Night clouds and nonequilibrium chemistry on the hot Jupiter WASP-43b” by Taylor J. Bell, Nicolas Crozet, and Patricio E. Kobelo, Laura Kreidberg, and Anjali A.A. Peet, and Michael T. Roman, and Joanna K. Barstow, Jasmina Plisic, Ludmila Carone, Louis-Philippe Collomb, Elsa Ducrot, Mark Hammond, João M. Mendonça, Julien I. Moses, Vivien Parmentier, Kevin B. Stevenson, Lucas Tintorier, Michael Chang, Natalie M. Batalha, Jacob L. Bean, Björn Beneke, Benjamin Charney, Katie L. Chubb, Bryce-Olivier Demaury, Peter Gao, Elspeth K. H. Lee, Mercedes Lopez-Morales, Giuseppe Morello, Emily Rauscher, David K. . Singh, Xianyu Tan, Olivia Vinot, Hannah R. Wakeford, Keshav Agarwal, Eva Maria Ahrer, Munaza K. Allam, Ruben Bayens, David Parrado, Claudio Cáceres, Arin L. Carter, Sarah L. Caswell, Ryan C. Challner, Ian JM Crosfield, Lyn Desain, Jean-Michel Desert, Ian Dobbs-Dixon, Akren Derrick, Nestor Espinosa, Adina D. Feinstein, Neil B. Gibson, Joseph Harrington, Christian Helling, Renew Hu, Nicholas Iero, Eliza M.-R. Compton, Sarah Kendrew, Thaddeus D. Komacek, Jessica Crick, Pierre-Olivier Lagage, Jeremy Leconte, Monica Lindell, Neil T. Lewis, Joshua D. Lothringer, Isaac Malski, Luigi Mancini, Megan Mansfield, Nathan J. Mayne, Thomas M. Evans Soma, Karan Molaverdkhani, Nikolai K. Nikolov, Matthew C. Nixon, Enrique Paley, Dominique J.M. Petit de la Roche, Carolyn Piollet, Diana Powell, Benjamin V. Rackham, Aaron D. Schneider, Maria E. Steinrock. Jake Taylor, Louis Wilbanks, Sergey N. Yurchenko, Xi Zhang, and Sebastian Ziba, April 30, 2024, Nature astronomy.
DOI: 10.1038/s41550-024-02230-x

The MIRI observation of WASP-43 b was conducted as part of the Webb Early Release Science programs, which provide researchers with a wide range of robust, open-access data to study a wide range of cosmic phenomena.

The James Webb Space Telescope is the world's leading space science observatory. Webb solves the mysteries of our solar system, looks beyond the distant worlds around other stars, and explores the mysterious structures and origins of our universe and our place in it. WEB is an international program led by NASA with its partners the European Space Agency (ESA).European Space Agency) and the Canadian Space Agency.