5 Oct 2021

 

Considered an ultra-hot Jupiter – a place where iron gets vaporized, condenses on the night-side and then falls from the sky like rain – the fiery, inferno-like WASP-76b exoplanet may be even more sizzling than scientists had realized.

An international team, led by researchers at University of Toronto, Cornell, and Queen’s University Belfast, reports the discovery of ionized calcium on the planet – in high-resolution spectra obtained with the Gemini North Observatory near the summit of Mauna Kea in Hawaii.

 

Hot Jupiters are so named for their high temperatures, due to proximity to their stars. WASP-76b, discovered in 2016, is a Jupiter-sized planet about 640 light-years from Earth, but so close to its F-type star, which is slightly hotter than the sun, the giant planet completes one orbit every 1.8 Earth days.

The research results are the first of a multi-year, Cornell-led project Exoplanets with Gemini Spectroscopy survey, or ExoGemS, that explores the diversity of planetary atmospheres.

 

“As we do ‘remote-sensing’ of dozens of exoplanets, spanning a range of masses and temperatures,” said co-author Ray Jayawardhana, the Harold Tanner Dean of the College of Arts and Sciences (A&S), and a professor of astronomy, “we will develop a more complete picture of the true diversity of alien worlds – from those hot enough to harbour iron rain to others with more moderate climates, from those heftier than Jupiter to others not much bigger than the Earth.

“It’s remarkable that with today’s telescopes and instruments, we can already learn so much about the atmospheres – their constituents, physical properties, presence of clouds and even large-scale wind patterns – of planets that are orbiting stars hundreds of light-years away,” Jayawardhana said.

 

The group spotted a rare trio of spectral lines in highly sensitive observations of the exoplanet WASP-76b’s atmosphere, to be published in the Astrophysical Journal Letters and presented on Oct. 5 at the annual meeting of the Division for Planetary Sciences of the American Astronomical Society.

“We’re seeing so much calcium, it’s a really strong feature,” said first author Emily Deibert, a doctoral student at the Dunlap Institute for Astronomy and Astrophysics and the University of Toronto, whose adviser is Jayawardhana.

 

“This spectral signature of ionized calcium could indicate that the exoplanet has very strong upper atmosphere winds,” Deibert said. “Or the atmospheric temperature on the exoplanet is much higher than we thought.”

Since WASP-76b is tidally locked – in that one side of it always faces the star – it has a permanent night side that sports a relatively cool 2,400-degree Fahrenheit average temperature. Its day side bulges toward the star and it has an average temperature at 4,400 degrees F.

 

Deibert and her colleagues examined the moderate temperature zone, on the planet’s limb between day and night. “The exoplanet moves fast on its orbit and that’s how we were able to separate its signal from starlight,” she said. “You can see that the calcium imprint on the spectra is moving quickly along with the planet.”

In terms of what’s next, Deibert says the team will carry out a similar analysis on other exoplanets, in the hopes that this will provide us with further insight into the physics and chemistry of their atmospheres.

 

“Ultimately, this survey will allow us to observe more than thirty exoplanets over the next few years,” Deibert explains.

“The insights we gain from these observations will help us to one day be able to study the atmospheres of Earth-like worlds.”

 

[Image]

(A) Artist’s impression of a hot Jupiter exoplanet.

(B) Artist’s impression of the extreme atmosphere of WASP-76b

(C) Star trails over Gemini North.