We are talking about the exoplanet WASP-76 b, which delighted researchers with a bright light show, better known as «gloria» — until now it has been observed only within the Solar System.
The planet of hell
WASP-76 b is located about 637 light years from Earth and was first discovered in 2013. The planet, which is about 90% of the mass of Jupiter (but about twice as wide), is believed to have destroyed its Mercury-sized neighbor in the past. Also, WASP-76 is extremely close to its star — one revolution around it takes 1.8 days.
In 2020, researchers discovered that the planet is tidally locked, meaning that one side is always facing its home star (just as the Moon faces the Earth). As a result, the temperatures of the illuminated side reach 2400 °C (that’s why the planet is hellish), while the dark side is — colder. This slight difference means that metals such as iron can vaporize on the bright side and then condense as rain on the dark side.
A bright spot
In a new article published in early April in the Astronomy & Astrophysics (via Live Science), the researchers analyzed new data on WASP-76 b collected by several spacecraft (including ESA’s «Cheops» satellite). Eventually, a strange bright spot of light was detected along the eastern edge of the exoplanet at the border where the planet’s permanent day and night meet.
The researchers speculate that this bright spot could be a gloria — a rare optical phenomenon that can be seen on Earth and usually consists of concentric iridescent rings forming a giant circle.
On Earth, gloria are formed when sunlight penetrates small holes between water molecules in clouds or fog, refracting the light and separating it into individual wavelengths. Rainbows work in a similar way — except that light is bent due to diffraction (i.e., when light bends around an obstacle instead of refracting, or when light bends as it passes through different media).
«Very special conditions are required», says lead author Olivier Demangeon, an astronomer at the Institute of Astrophysics and Space Sciences in Portugal. «Atmospheric particles must have a near-perfect spherical shape, be completely homogeneous and sufficiently stable».
And the correct orientation of the observer also plays a role. It is quite possible that under similar conditions the effect can be seen on other planets (astronomers have previously observed gloria on Venus).
«We need to look for more evidence to say convincingly that this is an intriguing «bright light» — rare gloria», — said Therese Lüftinger, an ESA astrophysicist who was not involved in the study. «We will likely need more powerful instruments, such as those on the James Webb Space Telescope».