Researchers hailing from the University of Exeter have made a compelling discovery after pointing the Hubble Space Telescope in the general direction of WASP-121b, a hot Jupiter-like exoplanet residing almost 900 light years away from Earth.
Image Credit: Engine House VFX, At-Bristol Science Centre, University of Exeter
To their surprise, the upper atmosphere of the exoplanet was glowing brightly, an effect thought to be related to how closely WASP-121b is orbiting its host star and its atmospheric composition.
Published in the journal Nature, the researchers elaborate on their findings.
They used a technique called spectroscopy to observe the exoplanet in different light wavelengths to see how the atmosphere would react to each. They found that the atmosphere glows in the infrared light spectrum, and not the visible light spectrum.
The host star's heat is getting trapped in the exoplanet’s atmosphere in excess amounts, which causes the glowing phenomenon. The circumstances warm up the residing gasses there, and water vapor also reacts with the heat; cooler water vapor blocks light, while hotter water vapor emits infrared light into space.
"The emission of light from water means the temperature is increasing with height," said study co-author Tiffany Kataria from NASA's Jet Propulsion Laboratory. "We're excited to explore at what longitudes this behavior persists with upcoming Hubble observations."
In a very cool three-dimensional interactive YouTube video uploaded by the University of Exeter, you can see what WASP-121b looks like and how it’s emitting light:
The team compares their findings to the chemistry of fireworks, which emit certain wavelengths of light as they lose energy. While fireworks emit visible colors of light, the water vapor in WASP-121b’s atmosphere emits infrared light, which we can’t see without the help of Hubble.
Worthy of note, it’s unusual even for hot Jupiter-like exoplanets to get hot enough for their atmospheres to glow like this. Most planets and exoplanets experience an atmospheric temperature increase of around 100º Fahrenheit when confronted by their star's light, but WASP-121b’s atmosphere heats up to more than 1,000º Fahrenheit above normal.
For this to happen, there must be something inside WASP-121b’s atmosphere that’s reacting further with the star’s light. Hot Jupiter-like exoplanets are commonly compared to brown dwarfs (otherwise known as failed stars), which might hold the key as to what exists in the exoplanet's atmosphere that's causing this.
One theory is that there could be excess amounts of vanadium oxide and titanium oxide in WASP-121b's atmosphere contributing to the heat retention. In this case, it would behave similarly to Earth's ozone layer, just that it holds several times more heat than our ozone layer does.
Without a doubt, the discovery of WASP-121b’s glowing atmosphere is raising more questions than it’s answering. More observations are planned with Hubble and other space observation equipment to study the exoplanet in new wavelengths in the future, and perhaps we'll receive some answers.
"This super-hot exoplanet is going to be a benchmark for our atmospheric models, and it will be a great observational target moving into the Webb era," said second study co-author, Hannah Wakeford from NASA's Goddard Space Flight Center.
With the James Webb Space Telescope going into space next year, maybe we'll soon be able to understand WASP-121b’s atmosphere, its composition, and why exactly it’s so much hotter than we’d expect it to be.