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James Webb Telescope revealed details of the climate of WASP-43 b, a distant gas giant, marked by extreme heat, dense clouds on the night side, and planetary-scale winds, in an observation used to study atmospheres outside the Solar System.
The James Webb Space Telescope enabled the mapping of the climate of WASP-43 b, a gas giant located about 280 light-years from Earth, where the atmosphere combines extreme temperatures, dense clouds on the night side, and equatorial winds estimated at approximately 8,000 km/h.
With dimensions similar to Jupiter, the planet orbits its star at a much closer distance than that between Mercury and the Sun, and because of this proximity, completes an orbit in just 19.5 hours, less than one Earth day.
The measurements were made with the MIRI instrument of the James Webb, which observes the universe in mid-infrared light, and allowed researchers to estimate temperatures, cloud cover, water vapor, and atmospheric circulation from the brightness variations of the system.
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The data indicate a planet divided between two temperature regimes, with the side permanently facing the star reaching about 1,250°C, a value sufficient to heat iron to the point of allowing its forging, while the opposite hemisphere is close to 600°C.
WASP-43 b has permanent day and night
WASP-43 b belongs to the class of so-called “hot Jupiters”, gaseous exoplanets similar in size to the largest planets in the Solar System, but subjected to intense heat by orbiting very close to their stars.
This type of orbit favors a condition known as synchronous rotation, in which the planet always keeps the same face towards the star, while the other side remains in constant night, without regular alternation between day and darkness as occurs on Earth.
The difference between these hemispheres helps explain, according to the analysis released by NASA, the contrasting behavior of the atmosphere, as the daytime side receives direct stellar radiation and appears relatively bright in the James Webb measurements.
In the nighttime hemisphere, on the other hand, the data points to a darker region in the infrared, associated with the presence of a high and thick layer of clouds that interferes with the thermal emission observed by the telescope.
Even without receiving direct light from the star, the nighttime side does not cool completely because very fast winds transport heat from the illuminated region and redistribute part of the energy around the planet.
This global circulation mixes gases and connects the two hemispheres, which prevents, according to the atmospheric models used in the study, the daytime side and the nighttime side from evolving in a completely isolated manner.
James Webb measured the climate using infrared light
The telescope did not capture a direct image of the planet, as WASP-43 b is distant, small compared to its star, and very close to its brightness, a condition that requires indirect observation methods.
The analysis occurred through the infrared light emitted by the system during the orbit, when different parts of the planet faced James Webb and produced measurable variations in the total observed brightness.
When the hottest side of the planet faces the telescope, the total brightness increases; when the nighttime hemisphere starts to dominate the observation field, the infrared emission decreases and allows comparison of the characteristics of each region.
The observations covered wavelengths between 5 and 12 microns, a range sensitive to the heat emitted by hot objects, and followed more than one complete orbit to create an approximate map of the temperature distribution around the planet.
The technique is based on the fact that hotter bodies emit more infrared radiation, allowing scientists to compare subtle changes in this emission to infer where there is more heat, cloud blockage, and atmospheric circulation.
Dense clouds change the reading of the nighttime side
The clouds on the nighttime side are among the elements identified in the study to explain the difference in brightness between the hemispheres, as the atmospheric coverage interferes with the thermal radiation emitted by deeper layers.
The analysis indicates that this high and dense layer blocks part of the thermal radiation from the lower atmosphere, making the nighttime region appear colder and darker in the infrared measurements made by James Webb.
In the daytime hemisphere, the observed behavior is different, as the atmosphere appears clearer and without signs of the same blockage caused by thick clouds, which reinforces the climatic asymmetry measured between the two sides of the planet.
This division shows, according to researchers, that a global average does not adequately describe WASP-43 b, because the permanently daytime and permanently nighttime regions present distinct atmospheric conditions.
Although they belong to the same planet, these hemispheres are controlled by different combinations of intense radiation, gas circulation, and cloud formation, factors that alter how heat is observed in each region.
The presence of water vapor was also identified at different phases of the orbit and helps characterize the composition of the atmosphere, as well as providing clues about cloud altitude and heat transport models.
Winds of 8,000 km/h indicate atmosphere in intense mixing
Another data point highlighted by the analysis is the significant absence of methane in the nighttime side measurements, a molecule that could appear in greater quantity at lower temperatures if the atmosphere were not being mixed rapidly.
According to NASA, the data indicate that atmospheric circulation occurs too quickly to allow this detectable accumulation, which helps explain the estimate of extremely fast equatorial winds on WASP-43 b.
This mixing was one of the clues used to estimate equatorial winds reaching about 5,000 miles per hour, equivalent to just over 8,000 km/h, a speed capable of transporting gases and heat on a planetary scale.
The winds move eastward and help connect the two hemispheres, keeping the atmosphere in permanent circulation even with one side always exposed to the star and the other always plunged into night.
The absence of methane does not indicate chemical simplicity, but suggests, according to the researchers’ interpretation, that reactions, temperatures, and atmospheric movements act together and hinder the expected chemical equilibrium in colder regions.
Study expands the analysis of atmospheres outside the Solar System
WASP-43 b had already been studied by telescopes like Hubble and Spitzer, but the sensitivity of James Webb allowed for more detailed observation of the planet in the infrared and expanded the reading of the global climate.
The combination of recent measurements, previous data, and three-dimensional models helped researchers more clearly separate the illuminated side, the dark side, and the circulation of gases around the planet.
The study demonstrates the Webb’s ability to investigate the atmospheres of worlds that are trillions of kilometers from Earth, measuring brightness variations, detecting molecules, and estimating circulation patterns without direct observation of the surface.
In the case of WASP-43 b, the short orbital period also favored observation because the planet completes a revolution around the star in less than one Earth day, allowing for quick comparison of different phases.
These measurements help test models used to interpret exoplanet atmospheres and can contribute to future analyses of smaller planets, including those with characteristics closer to rocky worlds.
The climate of WASP-43 b, according to observational data, has no direct parallel in the Solar System, as it combines enough heat to forge iron, nights covered by dense clouds, and supersonic winds in an atmosphere dominated by hydrogen and helium.
The discovery adds information to the study of the diversity of worlds outside the Solar System, showing a planet that maintains one face in permanent heat, another under continuous darkness, and an atmosphere driven by extreme currents.
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