Astronomers have discovered for the first time a rainbow-like phenomenon they believe is occurring on a planet outside our solar system, and it could reveal new insights about alien worlds.
Observations from the European Space Agency's Cheops Space Telescope, or Characterizing ExOplanet Satellite, discovered a "glory effect" on WASP-76b, an ultra-hot exoplanet 637 light-years from Earth.
The effect, often observed on Earth, consists of concentric, colorful rings of light, and occurs when light is reflected from clouds made of a uniform substance.
Beyond Earth, the Glory Effect was only visible on Venus until Cheops and other missions picked up an incredibly weak signal indicating it was occurring in the atmosphere of the hellishly hot WASP-76b. Based on the signal detected by Cheops, astronomers think the atmospheric phenomenon is aimed directly at Earth.
Researchers reported details of the observation on April 5 in the journal Astronomy & Astrophysics.
"There is a reason why glory has never been seen outside our solar system before: it requires very special conditions," said lead study author Olivier Demangeon, an astronomer at the Institute of Astrophysics and Space Sciences in Portugal, in a statement. "First, you need atmospheric particles that are almost perfectly spherical, completely uniform and stable enough to be observed for long periods of time. The planet's nearby star should shine directly on it, with the observer - here Cheops - pointing in exactly the right direction."
A wild, scorching planet
WASP-76b has intrigued astronomers since its discovery in 2013.
The exoplanet orbits closely around its host star and the intense heat and radiationreceived from that sun-like star - more than 4,000 times the amount of radiation that Earth gets from our sun - has caused WASP-76b to inflate, making it almost twice the size of Jupiter, the largest planet in our solar system.
The planet is tidally linked to its star, meaning that one side, known as the day side, always faces the star, while the other side of the planet is permanently at night.
The dayside of WASP-76B reaches scorching temperatures of 4,352 degrees Fahrenheit (2,400 degrees Celsius). Elements that normally form rocks on Earth melt and evaporate on the day side before condensing to form clouds that release molten iron rain on the night side.
Astronomers decided to use a slew of observatories, including Cheops, the Hubble Space Telescope, the now-retired Spitzer Space Telescope and NASA's planet-hunting TESS mission, to study what appeared to be a light imbalance that occurred when WASP-76b was orbiting the earth turned. for his guest star.
Combined data from Cheops and TESS, or the Transiting Exoplanet Survey Satellite, indicated that the anomaly may have been due to something intriguing happening in the atmosphere above the dayside.
Cheops collected data from WASP-76b as the planet passed in front of its star, making 23 observations in 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. Meanwhile, less light was released from the western terminator.
"This is the first time such a sharp change has been observed in an exoplanet's brightness, its 'phase curve'," Demangeon said. "This discovery leads us to hypothesize that this unexpected glow could be caused by a strong, localized and anisotropic (direction-dependent) reflection - the glory effect."
Demangeon said he is thrilled to be involved in the first detection of this kind of light coming from an exoplanet.
"It was such a special feeling, a special satisfaction that doesn't happen every day," he said.
Colorful light on alien worlds
Glory and rainbows are not the same. Rainbows are created when light is bent as it passes successively through two media of different densities, such as from air to water. As the light is bent, it breaks into different colors, creating an arc-shaped rainbow.
But the glory effect occurs when light moves through a narrow opening and bends, creating colorful, patterned rings.
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 replenishing. Regardless, the presence of such clouds suggests that the planet's atmosphere has a stable temperature.
The nature of what exactly 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.
"What is important to keep in mind is the incredible scale of what we are witnessing," Matthew Standing, a European Space Agency researcher who studies exoplanets, said in a statement. Standing was not involved in the study.
"WASP-76b is several hundred light years away - an intensely hot gas giant planet likely raining molten iron," Standing said. "Despite the chaos, it seems that (researchers) have discovered the potential signs of glory. It is an incredibly weak signal."
If astronomers can detect the faint signal of a phenomenon like a glory from hundreds of light-years away, it may also be possible in the future to detect the presence of sunlight reflecting off alien water bodies, the researchers said.
"Further evidence is needed to say conclusively that this intriguing 'extra light' is a rare glory," Theresa Lueftinger, project scientist for the European Space Agency's Ariel mission, said in a statement. She was not involved in the investigation.
Ariel, or the Atmospheric Remote-sensing Infrared Exoplanet Large survey, is expected to launch in 2029 to study the atmospheres of a large, diverse selection of exoplanets.
Lueftinger said she believes the James Webb Space Telescope or Ariel could help prove the presence of the Glory Effect on WASP-76b.
"We might even find more gloriously revealing colors coming from other exoplanets," she said.
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