Scientists have found early signs of something called the “glory effect” on a planet outside of our solar system for the first time. The glory effect causes colorful concentric rings of light and is similar to a rainbow. But it only happens under special conditions.

The glory happens when light reflects off clouds made of perfectly uniform, spherical particles. Like a rainbow, it forms when light passes through a small opening, like water droplets in clouds or fog. This causes the light to bend and diffract, making circular patterns.

Data analyzed by astronomers, including some from the University of Warwick, suggests this happens in the super-hot atmosphere of the giant gas planet WASP-76b which is about 637 light years away from Earth.

Observations from the European Space Agency’s CHEOPS Exoplanet Characterization Satellite show there could be “glory” between the unbearable heat on WASP-76b’s day side that faces its sun and the endless night on its dark side.

Night side of the exoplanet WASP-76b. Iron vapor condenses into iron droplets
Night side of the exoplanet WASP-76b. Iron vapor condenses into iron droplets. Credit: Martin Kornmesser / ESO

This effect, often seen on Earth, has only been seen once before on another planet – Venus. If confirmed, this would be the first known glory outside our solar system and it would reveal more about the nature of this mysterious exoplanet.

Co-author Thomas Wilson from the University of Warwick said, We’ve never seen these colorful concentric rings on an exoplanet before. So if future studies can confirm this first exoplanetary glory, it would make WASP-76b a truly unique world, and give us a beautiful tool to understand the atmospheres of distant exoplanets and how habitable they might be.

Lead author Olivier Demangeon from the Institute of Astrophysics and Space Sciences in Portugal said there’s a good reason we haven’t seen glory outside our solar system before – it requires very special conditions. It needs atmospheric particles that are almost perfectly spherical and uniform, and stable enough to observe for a long time. The planet’s nearby star must shine directly on it, with the observer in just the right orientation.

WASP-76b is a “hot Jupiter” type planet similar to Jupiter but smaller. Though less massive than Jupiter, it’s almost twice as large due to intense radiation from its star causing it to swell up. Since its 2013 discovery, WASP-76b has shown its strange hellish environment – one side always faces the star with temperatures up to 2,400 degrees Celsius where rocks would melt. Elements form clouds of molten iron rain on the cooler nightside.

Simulated views of the glory of Venus and Earth
Simulated views of the glory of Venus and Earth. Credit: ESA

But scientists were puzzled by an apparent asymmetry in WASP-76b’s “limbs”, the outer regions seen passing in front of its star. Intensive monitoring by CHEOPS of 23 crossings over three years revealed a surprising increase in light from the planet’s eastern “terminator”, the boundary between night and day. This helped determine the signal’s origin.

Demangeon added, This is the first time such a sharp change in an exoplanet’s brightness has been detected. This discovery leads to the hypothesis that this unexpected brightening could be caused by a strong, localized, direction-dependent reflection: the glory effect.

The NASA/ESA/CSA James Webb Space Telescope may now confirm this is indeed glory, which would imply WASP-76b’s atmosphere must be stable enough over time for perfectly spherical water cloud droplets crucial to glory formation.


Sources

University of Warwick | O.D.S. Demangeon, P.E. Cubillos, et al., Asymmetry in the atmosphere of the ultra-hot Jupiter WASP-76 b. Astronomy & Astrophysics, vol.684, doi.org/10.1051/0004-6361/202348270


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