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A rainbow-like phenomenon may glow on the hellish exoplanet WASP-76b

A rainbow-like phenomenon may glow on the hellish exoplanet WASP-76b

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Astronomers have discovered what they believe is a rainbow-like phenomenon occurring on a planet outside our solar system for the first time, and it could reveal new insights about alien worlds.

Observations by the European Space Agency's Cheops Space Telescope, or exoplanet satellite, revealed a “glory impact” on WASP-76b, an extremely hot exoplanet located 637 light-years from Earth.

Most often seen on Earth, the effect consists of Concentric colored rings of light, which occur when light reflects off clouds made of uniform material.

Beyond Earth, the Glory Impact had only been seen on Venus until Khufu and other missions picked up an incredibly faint signal indicating it was occurring in the superheated atmosphere of planet WASP-76b. Based on the signal detected by Khufu, astronomers believe that the atmospheric phenomenon is facing the Earth directly.

The researchers reported details of the observation April 5 in the journal Astronomy and astrophysics.

“There is a reason why glory has never been seen outside our solar system, and that is that it requires very strange conditions,” lead study author Olivier Demanjon, an astronomer at the Institute of Astrophysics and Space Sciences in Portugal, said in a statement. “First, we need atmospheric molecules that are perfectly spherical, perfectly uniform and stable enough to observe them over a long period. The star close to the planet needs to shine directly on it, with the observer – here Khufu – facing in exactly the right direction.”

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WASP-76b has aroused the interest of astronomers since its discovery in 2013.

The exoplanet orbits closely around its host star, and has a high temperature and radiation This Sun-like star—more than 4,000 times the amount of radiation Earth receives from our Sun—has caused WASP-76b to swell, making it twice the size of Jupiter, the largest planet in our solar system.

C. Wilson/B. Lavin/ESA

The simulation view shows the glory as it might appear on Venus (left) and Earth.

The planet is tidally locked to its star, meaning that one side, known as the day side, always faces the star, while the other side of the planet is always at night.

The dayside of WASP-76B reaches scorching temperatures of 4,352°F (2,400°C). Elements that normally form rocks on Earth melt and evaporate on the dayside before condensing and forming clouds that release rains of molten iron on the nightside.

Astronomers decided to focus a whole host of observatories, including Cheops, the Hubble Space Telescope, the now-retired Spitzer Space Telescope, and NASA's planet-hunting TESS mission, to study what appears to be a light imbalance. It happened as WASP-76b orbited in front of its host star.

Data combined from Cheops and TESS, or the Transiting Exoplanet Survey Satellite, indicated that this anomaly might be due to something interesting happening in the atmosphere above the dayside.

Khufu captured data from WASP-76b as the planet passed in front of its star, and made 23 observations over three years.

When astronomers looked at the data, they noticed an unusual increase in light coming from the planet's eastern “terminator,” or the boundary light between the day and night sides. At the same time, less light was released from the Western Terminator.

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“This is the first time such a sharp change in the brightness of an exoplanet, or its phase curve, has been detected,” Demangione said. “This discovery leads us to hypothesize that this unexpected glow could be caused by a strong, localized, anisotropic (direction-dependent) reflection – the glory effect.”

Demangione said he was very happy to participate in the first discovery of this type of light coming from an exoplanet.

“It was a special feeling, a special satisfaction that doesn't happen every day,” he said.

Glory and rainbows are not the same thing. A rainbow occurs when light bends as it passes successively through two media of different densities, such as air to water. When light is bent, it breaks into different colors, forming an arcuate rainbow.

But the glory effect occurs when light moves through a narrow aperture and bends, creating patterned rings of color.

If astronomers really see the glory effect on WASP-76b, it means the planet has persistent clouds made of perfectly spherical droplets, or clouds that are constantly renewing. In either case, the presence of such clouds indicates that the temperature of the planet's atmosphere is stable.

The exact nature of what is in the clouds on WASP-76b remains a mystery, but it could be iron, as the element has previously been detected in clouds on the planet.

M. Kornmesser/ESO

An artist's illustration shows a night view of the exoplanet WASP-76b, with iron falling from the sky.

“What is important to keep in mind is the astonishing scale of what we are witnessing,” Matthew Standing, a research fellow at the European Space Agency who studies exoplanets, said in a statement. Permanent did not participate in the study.

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“WASP-76b is several hundred light-years away, and it is a gas giant planet so hot that it would likely rain molten iron,” Standing said. “Despite the chaos, (researchers) seem to have detected potential signs of glory. It's an incredibly faint sign.

If astronomers can observe the faint signal of a phenomenon like glory from hundreds of light-years away, detecting the presence of sunlight reflecting off extraterrestrial bodies of water may also be possible in the future, according to the researchers.

“Additional evidence is needed to definitively say that this interesting ‘extra light’ is a rare glory,” Teresa Loftinger, project scientist for ESA’s Ariel mission, said in a statement. She did not participate in the study.

Ariel, or the Large Infrared Atmospheric Remote Sensing Exoplanet Survey, is expected to launch in 2029 to study the atmospheres of a large variety of exoplanets.

Loftinger said she believes the James Webb Space Telescope or Ariel may be able to help prove the existence of the Glory Effect on WASP-76b.

“We could find even more amazing colors shining from other exoplanets,” she said.