WASP-76b is a strange world. Located 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 reveal it may even have a rainbow-like optical phenomenon that’s only been observed on Earth and Venus.
The European Space Agency’s Cheops satellite picked up signs of the ‘glory effect’ on a planet outside the solar system for the first time, spotting colorful rings of light on WASP-76b. A glory takes place when light passes between water droplets in clouds or fog, creating an optical effect that looks like a rainbow halo.
“There’s a reason no glory has been seen before outside our Solar System – it requires very peculiar conditions,” Olivier Demangeon, astronomer at the Institute of Astrophysics and Space Sciences in Portugal and lead author of a study published in Astronomy & Astrophysics said in a statement.
“First, you need atmospheric particles that are close-to-perfectly spherical, completely uniform and stable enough to be observed over a long time. The planet’s nearby star needs to shine directly at it, with the observer – here Cheops – at just the right orientation,” he added.
As if WASP-76b weren’t weird enough. The exoplanet orbits a star that’s 50% more massive and 500 degrees Celsius hotter than the Sun. WASP-76b is tidally locked to its star, meaning that one side is permanently bathed in light and scorching heat. It sits around 12 times closer than Venus orbits the Sun. This extreme position has heated the planet’s atmosphere to 2,000 degrees C, causing it to puff up to almost six times the volume of Jupiter (it’s nearly twice as wide but with less mass).
Oh, and it also happens to rain iron on WASP-76b. Due to the difference in temperature between the day and night side, iron melts on the planet’s day side and condenses into clouds when it reaches the darker, cooler night side.
Choeps, or the Characterising ExOplanet Satellite, has been observing WASP-76b for three years and has detected a surprising increase in the amount of light coming from the the boundary where night meets day. “This discovery leads us to hypothesise that this unexpected glow could be caused by a strong, localised and anisotropic (directionally dependent) reflection – the glory effect,” Demangeon said.
The scientists will still need to gather more evidence that this extra light really is the glory effect, and they plan to use an instrument on board the Webb Space Telescope to do so. ESA’s upcoming Ariel mission, which is set to launch in 2029 to create the first chemical survey of exoplanets, could also be used to prove the rare phenomenon on WASP-76b.
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