Researchers from the University of Warwick have observed signs of the rainbow-like ‘glory lights’ effect on a distant planet outside our Solar System for the first time.
Glory lights are colourful concentric rings of light that occur only under peculiar conditions.
They occur when light is reflected off clouds made up of a perfectly uniform, but so far unknown, substance.
The effect, similar to a rainbow, forms when light passes between a narrow opening, for example, between water droplets in clouds or fog, causing it to diffract and create ring-like patterns.
Data analysed by astronomers suggests this phenomenon is beaming from the hellish atmosphere of ultra-hot gas giant WASP-76b some 637 light-years away.
Glory lights could reveal crucial information about the distant planet
Observations from the European Space Agency’s Characterising Exoplanet Satellite (CHEOPS) suggest that between the unbearable heat and light of exoplanet WASP-76b’s sunlit face and the endless night of its dark side, there may be glory lights.
Although the effect is often seen on Earth, it has only been found once on another planet, Venus. If confirmed, this first glory outside the Solar System will reveal more about the nature of this puzzling distant planet.
Co-author Thomas Wilson from the University of Warwick commented: “Never before have we seen these colourful, concentric rings on an extrasolar body.
“This first exoplanetary glory, if confirmed with future studies, would make WASP-76b a truly unique body and give us a beautiful tool for understanding the atmospheres of distant exoplanets and their potential habitability.
“There’s a reason glory lights have never been seen outside our Solar System – it requires very peculiar conditions,” added Olivier Demangeon from the Institute of Astrophysics and Space Sciences, Portugal.
“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 at just the right orientation.”
Uncovering the mysteries of WASP-76b
WASP-76b is an ultra-hot Jupiter-like planet. While it has less mass than our striped cousin, it is almost double its size.
Tightly orbiting its host star twelve times closer than scorched Mercury orbits our Sun, the exoplanet’s large size is caused by it being ‘puffed up’ by intense radiation.
Since its discovery in 2013, WASP-76b’s bizarre environment has emerged. One side of the planet always faces the Sun, reaching temperatures of 2400°C. Here, elements that would form rocks on Earth melt and evaporate, only to condense on the slightly cooler night side, creating iron clouds that drip molten iron rain.
However, scientists have been puzzled by an apparent asymmetry, or wonkiness, in WASP-76b’s ‘limbs’ – its outermost regions seen as it passes in front of its host star.
Cheops intensively monitored WASP-76b as it passed in front of and around its Sun-like star. After 23 observations over three years, the data showed a surprising increase in the amount of light coming from the planet’s eastern ‘terminator’ – the boundary where night meets day. This allowed scientists to determine the origin of the glory lights.
Demangeon explained: “This is the first time that such a sharp change has been detected in the brightness of an exoplanet. This discovery leads us to hypothesise that this unexpected glow could be caused by a strong, localised and directionally dependent reflection – the glory effect.”
NASA’s James Webb Space Telescope (JWST) could now be used to officially confirm that these are glory lights.
Confirmation would imply that the temperature of WASP-76b’s atmosphere must be stable over time, enabling the presence of clouds made up of perfectly spherical water droplets crucial to glory lights formation.
