Swiss space telescope observes exoplanet ‘rainbow’

WASP-76 (the «Sun» of WASP-76b) is a yellow and white main sequence star like our Sun, but different stars create glories with different colours and patterns. © ESA, work performed by ATG under contract for ESA. CC BY-SA 3.0 IGO

The Swiss space telescope CHEOPS has found a type of rainbow on a planet 637 light years away. The observation of a so-called “glory” is likely the first evidence of this phenomenon outside our solar system.  

However, further investigations are needed to confirm whether the observation on the planet known as “WASP-76b” truly was a glory, the University of Geneva, which runs scientific operations for CHEOPS, announced on Friday. The researchers presented their discovery in a study in the journal Astronomy & Astrophysics.  

A glory is a rainbow-like scattering of light that looks like a halo. It occurs when light is reflected as it passes through a cloud of perfectly uniform droplets. In the case of Earth, these droplets are made of water.  

Drops of iron?  

However, the nature of these droplets on WASP-76b is still a mystery, according to the university. They could be made of iron, as this element has already been detected on the surface of the planet.

“The reason why such a glow has never been observed outside our solar system is that this phenomenon requires very specific conditions,” explained first author Olivier Demangeon in the press release. “First of all, the atmospheric particles must be almost perfectly spherical, completely uniform and sufficiently stable to be observed throughout a long time. These droplets have to be directly illuminated by the planet’s host star, and the observer – in this case CHEOPS – must be in the right position.” 

The discovery of such tiny phenomena at such a great distance will enable scientists to recognise other equally important phenomena, according to the University of Geneva. For example, the reflection of starlight on liquid lakes and oceans, which is a necessary condition for habitability.  

2,400 degrees Celsius 

WASP-76b has been closely scrutinised by astronomers since its discovery in 2013. Examinations have revealed that the gas giant is characterised by extreme conditions, with iron rain and temperatures of up to 2,400°C. Chemical elements that would form rocks on Earth melt and vaporise there, before condensing on the slightly cooler night side and forming clouds. 

Adapted from German by DeepL/kc/ts

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