WASP-43b is cloudy on the nightside and clear on the dayside, with equatorial winds howling around the planet at 8,050 km per hour (5,000 mph).
WASP-43b is a gaseous exoplanet the size of Jupiter but with double the mass.
This alien world is located about 260 light-years away in the constellation of Sextans.
WASP-43b lies so close to its host star, the orange dwarf star WASP-43, that it completes an orbit in just 19.5 hours.
It is also gravitationally locked so that it keeps one hemisphere facing the star.
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-43b has been observed with numerous telescopes, including the NASA/ESA Hubble Space Telescope and NASA’s now-retired Spitzer Space Telescope.
“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,” said Dr. Taylor Bell, an astronomer at the Bay Area Environmental Research Institute.
“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.”
Although WASP-43b is too small, dim, and close to its star for a telescope to see directly, its short orbital period 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.
In their study, Dr. Bell and colleagues used Webb’s Mid-Infrared Instrument (MIRI) 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…
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