Stratosphere Detected around Hot Jupiter WASP-121b

Gwen Vasquez
August 3, 2017

A "glowing" water atmosphere has been detected on an enormous super-hot exoplanet, offering the strongest evidence yet for a stratosphere on a planet outside our solar system.

"The stratosphere of WASP-121b is so hot it can make water vapour glow, which is the basis for our analysis".

"This result is exciting because it shows that a common trait of most of the atmospheres in our solar system - a warm stratosphere - also can be found in exoplanet atmospheres", Mark Marley, the study's co-author based at NASA's Ames Research Centre explains. Water vapour in a planet's atmosphere behaves in predictable ways depending on its temperature.

"Theoretical models have suggested that stratospheres may define a special class of ultra-hot exoplanets, with important implications for the atmospheric physics and chemistry", said Tom Evans, research fellow at the University of Exeter and lead author of the study. But at higher temperatures, the water molecules glow.

In Earth's stratosphere, ozone gas traps ultraviolet radiation from the sun, which raises the temperature of this layer of atmosphere. At 4,600 degrees Fahrenheit, the top of its atmosphere can boil some metals.

When scientists inspected WASP-121b with the Hubble telescope, they found that water vapor at the top of its atmosphere was emitting light.

WASP-121b is almost double the size of Jupiter and it is what's known as a hot Jupiter, a gas giant with an orbit that hugs its star. The latest study by astronomers is believed to be the best evidence so far, as it is the pioneering proof about the signature of hot water molecules which the researchers observed.

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The exoplanet orbits its host star every 1.3 days, and the two bodies are about as close as they can be to each other without the star's gravity ripping the planet apart.

The scientists studied how the different molecules present in the atmosphere of the WASP-121b reacted to specific wavelengths of light.

A team of astronomers from the University of Exeter and the University of Maryland discovered glowing water molecules while surveying Hubble's observations of WASP-121b's atmosphere. "Our observations support this picture". From the amount of light escaping to space, researchers were able to determine that temperature is increasing with height. Methane in the stratosphere of Jupiter and Saturn's moon Titan has a similar effect. Most stratospheres feature a temperature difference of 100 degrees Celsius.

"The very existence of exoplanets have stratospher still could only guess; some suspicions on this score were given the previously obtained spectra of the same WASP-121b, but the clarity was not as long as astronomers had not sent her a wide-angle camera of Hubble WFC3", - stated in the publication.

Co-author Dr Nikolay Nikolov, also at Exeter, said: "We've measured a strong rise in the temperature of WASP-121b's atmosphere at higher altitudes, but we don't yet know what's causing this dramatic heating". They are good for trapping heat at visible wavelengths and considering how hot it gets on the planet, the conditions are right to maintain them in a gaseous state.

Scientists have detected for the first time a large exoplanet with "smoking gun evidence" of a stratosphere.

NASA's forthcoming James Webb Space Telescope will be able to follow up on the atmospheres of planets like WASP-121b with higher sensitivity than any telescope now in space.

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