WASP-76b is a strange world. Several hundred light-years away, the Jupiter-like planet is tidally locked to its star, has scorching temperatures and rains molten iron. Recent observations of the hot gas giant show that it may even exhibit a rainbow-like optical phenomenon previously only observed on Earth and Venus.
The European Space Agency’s Cheops satellite detected signs of the “glory effect” on a planet outside the solar system for the first time, detecting colorful rings of light on WASP-76b. A glory occurs when light passes between water droplets in clouds or fog, creating an optical effect that looks like a rainbow halo.
“There is a reason why there has never been a glorious world outside our solar system – it requires very special conditions,” says Olivier Demangeon, an astronomer at the Institute of Astrophysics and Space Sciences in Portugal and lead author of a book study published in Astronomy & Astrophysics, said in a opinion.
“First, you need atmospheric particles that are almost perfectly spherical, completely uniform, and stable enough to be observed over long periods of time. The planet’s nearby star must shine directly on it, with the observer – here Cheops – facing exactly the right way,” he added.
As if WASP-76b wasn’t strange enough. The exoplanet orbits a star that is 50% more massive and 500 degrees Celsius hotter than the Sun. WASP-76b is tidally locked to its star, meaning one side is permanently bathed in light and searing heat. It is about twelve times closer than Venus orbits the Sun. This extreme position has heated the planet’s atmosphere to 2,000 degrees Celsius, causing it to expand to almost six times the volume of Jupiter (it is almost twice as wide but with less mass).
Oh, and it’s also raining iron on WASP-76b. Because of the temperature difference between the day and night sides, iron on the day side of the planet melts and condenses into clouds when it reaches the darker, cooler night side.
Choeps, or the characterizing ExOplanet satellite, has been observing WASP-76b for three years and has noticed a surprising increase in the amount of light coming from the boundary between night and day. “This discovery leads us to hypothesize that this unexpected glow could be caused by a strong, localized and anisotropic (directional) reflection – the Glory effect,” said Demangeon.
Scientists still need to gather more evidence that this extra light is really the Glory effect, and they plan to use an instrument aboard the Webb Space Telescope to do so. ESA’s upcoming Ariel mission, due to launch in 2029 to carry out the first chemical study of exoplanets, could also be used to detect the rare phenomenon on WASP-76b.
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