From The NASA/ESA/CSA James Webb Space based Infrared Astronomy Telescope
4.30.24
Margaret W. Carruthers
Space Telescope Science Institute, Baltimore, Maryland
Christine Pulliam
Space Telescope Science Institute, Baltimore, Maryland
Hot Gas-Giant Exoplanet WASP-43 b (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 into view as it orbits. The system appears brightest when the hot dayside is facing the telescope, just before and after the secondary eclipse when the planet passes behind the star. The system grows dimmer as the planet continues its orbits and the nightside rotates into view. After the transit when the planet passes in front of the star, blocking some of the starlight, the system brightens again as the dayside rotates back into view.
This graph shows more than 8,000 measurements of 5- to 12-micron mid-infrared light captured over a single 24-hour observation using the low-resolution spectroscopy mode on Webb’s MIRI (Mid-Infrared Instrument). By subtracting the amount of light contributed by the star, astronomers can calculate the amount coming from the visible side of the planet as it orbits. Webb was able to detect differences in brightness as small as 0.004% (40 parts per million).
Since the amount of mid-infrared light given off by an object is directly related to its temperature, astronomers were able to use these measurements to calculate the average temperature of different sides of the planet.
Credits: NASA, ESA, CSA, Ralf Crawford (STScI)
Science: Taylor Bell (BAERI), Joanna Barstow (The Open University), Michael Roman (University of Leicester)
Hot 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-planet system by MIRI (the Mid-Infrared Instrument) on NASA’s James Webb Space Telescope. In general, the hotter an object is, the more mid-infrared light it gives off.
Because WASP-43 b orbits so close to its star (about 1.3 million miles, or 0.014 astronomical units), it is tidally locked: One side faces the star at all times, receiving continuous radiation, while the other faces away from the star in permanent darkness. This results in a clear temperature difference between the dayside and nightside. The amount of infrared light detected from the planet is greatest when the hot dayside faces the telescope, just before and after it passes behind the star (a phenomenon known as a secondary eclipse). The planet appears much dimmer in infrared light when the cooler nightside faces the telescope, as it moves across the star (the transit).
The exact difference in temperature, however, also depends on factors such as wind speeds and cloud cover. Based on the MIRI observations, WASP-43 b has an average temperature of about 2,280°F (1,250°C) on the dayside and 1,115°F (600°C) on the nightside. This is consistent with strong winds that carry heat around from the dayside to the nightside, and the presence of nightside clouds that prevent heat energy from escaping to space.
The temperature maps were made by carefully analyzing the change in temperature as different parts of the planet rotate into and out of view. The research indicates that the hottest point on the planet is not the point that receives the most light from the star (the substellar point, where the star is straight above in the sky). Instead, it is shifted about 7 degrees eastward. (This is why the maps look slightly off-center.) This is a result of strong equatorial winds, which blow at speeds upwards of 5,000 miles per hour, moving the hot air horizontally before it can radiate energy back out to space.
Credits: NASA, ESA, CSA, Ralf Crawford (STScI)
Science: Taylor Bell (BAERI), Joanna Barstow (The Open University), Michael Roman (University of Leicester)
Summary
WASP-43 b is cloudy on the nightside and clear on the dayside, with equatorial winds howling around the planet at 5,000 miles per hour.
Artist’s depiction of hot Jupiter WASP-43 b
Sometimes not finding something is just as exciting and useful as finding it. Take hot Jupiter WASP-43 b, for example. This tidally locked world has a searing-hot, permanent dayside and a somewhat cooler nightside. Astronomers using Webb to map the temperature and analyze the atmosphere around the planet expected to detect methane, a common carbon molecule, on the nightside. But there is clearly no sign of it. Why? The result suggests that supersonic winds of hot gas are blowing around from the dayside, thoroughly churning up the atmosphere, and preventing the chemical reactions that would otherwise produce methane on the nightside.
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An international team of researchers has successfully used NASA’s James Webb Space Telescope to map the weather on the hot gas-giant exoplanet WASP-43 b.
Precise brightness measurements over a broad spectrum of mid-infrared light, combined with 3D climate models and previous observations from other telescopes, suggest the presence of thick, high clouds covering the nightside, clear skies on the dayside, and equatorial winds upwards of 5,000 miles per hour mixing atmospheric gases around the planet.
The investigation is just the latest demonstration of the exoplanet science now possible with Webb’s extraordinary ability to measure temperature variations and detect atmospheric gases trillions of miles away.
Tidally Locked “Hot Jupiter”
WASP-43 b is a “hot Jupiter” type of exoplanet: similar in size to Jupiter, made primarily of hydrogen and helium, and much hotter than any of the giant planets in our own solar system. Although its star is smaller and cooler than the Sun, WASP-43 b orbits at a distance of just 1.3 million miles – less than 1/25th the distance between Mercury and the Sun.
With such a tight orbit, the planet is tidally locked, with one side continuously illuminated and the other in permanent darkness. Although the nightside never receives any direct radiation from the star, strong eastward winds transport heat around from the dayside.
Since its discovery in 2011, WASP-43 b has been observed with numerous telescopes, including NASA’s Hubble and now-retired Spitzer space telescopes.
“With Hubble, we could clearly see that there is water vapor on the dayside. Both Hubble and Spitzer suggested there might be clouds on the nightside,” explained Taylor Bell, researcher from the Bay Area Environmental Research Institute and lead author of a study published today in Nature Astronomy.
See the science paper for instructive material with images.
“But we needed more precise measurements from Webb to really begin mapping the temperature, cloud cover, winds, and more detailed atmospheric composition all the way around the planet.”
Mapping Temperature and Inferring Weather
Although WASP-43 b is too small, dim, and close to its star for a telescope to see directly, its short orbital period of just 19.5 hours makes it ideal for phase curve spectroscopy, a technique that involves measuring tiny changes in brightness of the star-planet system as the planet orbits the star.
Since the amount of mid-infrared light given off 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) [below] to measure light from the WASP-43 system every 10 seconds for more than 24 hours. “By observing over an entire orbit, we were able to calculate the temperature of different sides of the planet as they rotate into view,” explained Bell. “From that, we could construct a rough map of temperature across the planet.”
The measurements show that the dayside has an average temperature of nearly 2,300 degrees Fahrenheit (1,250 degrees Celsius) – hot enough to forge iron. Meanwhile, the nightside is significantly cooler at 1,100 degrees Fahrenheit (600 degrees Celsius). The data also helps locate the hottest spot on the planet (the “hotspot”), 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 occurs because of supersonic winds, which move heated air eastward.
“The fact that we can map temperature in this way is a real testament to Webb’s sensitivity and stability,” said Michael Roman, a co-author from the University of Leicester in the U.K.
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 nightside is probably covered in a thick, high layer of clouds that prevent some of the infrared light from escaping to space. As a result, the nightside – while very hot – looks dimmer and cooler than it would if there were no clouds.
Missing Methane 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 figure out exactly which molecules we’re seeing and put some limits on the abundances,” said Joanna Barstow, a co-author from the Open University in the U.K.
The spectra show clear signs of water vapor on the nightside as well as the dayside of the planet, providing additional information about how thick the clouds are and how high they extend in the atmosphere.
Surprisingly, the data also shows a distinct lack of methane anywhere in the atmosphere. Although the dayside is too hot for methane to exist (most of the carbon should 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 reaching something like 5,000 miles per hour,” explained Barstow. “If winds move gas around from the dayside to the nightside and back again fast enough, there isn’t enough time for the expected chemical reactions to produce detectable amounts of methane on the nightside.”
The team thinks that because of this wind-driven mixing, the atmospheric chemistry is the same all the way around the planet, which wasn’t apparent from past work with Hubble and Spitzer.
The MIRI observation
of WASP-43 b was conducted as part of the Webb Early Release Science
programs, which are providing researchers with a vast set of robust, open-access data for studying a wide array of cosmic phenomena.
See the full article here .
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Webb is a large infrared telescope with a 6.5-meter primary mirror. Webb was finally launched December 25, 2021, ten years late. Webb will be the premier observatory of the next decade, serving thousands of astronomers worldwide. It will study every phase in the history of our Universe, ranging from the first luminous glows after the Big Bang, to the formation of solar systems capable of supporting life on planets like Earth, to the evolution of our own Solar System.
Webb is the world’s largest, most powerful, and most complex space science telescope ever built. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it.
Webb was formerly known as the “Next Generation Space Telescope” (NGST); it was renamed in Sept. 2002 after a former NASA administrator, James Webb.
Webb is an international collaboration between National Aeronautics and Space Administration, the European Space Agency (ESA), and the Canadian Space Agency (CSA). The NASA Goddard Space Flight Center managed the development effort. The main industrial partner is Northrop Grumman; the Space Telescope Science Institute operates Webb.
Several innovative technologies have been developed for Webb. These include a folding, segmented primary mirror, adjusted to shape after launch; ultra-lightweight beryllium optics; detectors able to record extremely weak signals, microshutters that enable programmable object selection for the spectrograph; and a cryocooler for cooling the mid-IR detectors to 7K.
There are four science instruments on Webb: The Near InfraRed Camera (NIRCam), The Near InfraRed Spectrograph (NIRspec), The Mid-InfraRed Instrument (MIRI), and The Fine Guidance Sensor/ Near InfraRed Imager and Slitless Spectrograph (FGS-NIRISS).
Webb’s instruments are designed to work primarily in the infrared range of the electromagnetic spectrum, with some capability in the visible range. It will be sensitive to light from 0.6 to 28 micrometers in wavelength.
Webb has four main science themes: The End of the Dark Ages: First Light and Reionization, The Assembly of Galaxies, The Birth of Stars and Protoplanetary Systems, and Planetary Systems and the Origins of Life.
Launch was December 25, 2021, ten years late, on an Ariane 5 rocket. The launch was from Arianespace’s ELA-3 launch complex at European Spaceport located near Kourou, French Guiana. Webb is located at the second Lagrange point, about a million miles from the Earth.
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