Using high-resolution spectra obtained with GRACES at the Gemini North Observatory, astronomers have detected ionized calcium in the atmosphere of the ultrahot Jupiter WASP-76b. This result is the first of the Exoplanets with Gemini Spectroscopy survey (ExoGemS) that explores the diversity of planetary atmospheres.
This illustration shows a night-side view of the exoplanet WASP-76b. To the left of the image, we see the evening border of the exoplanet, where it transitions from day to night. Image credit: M. Kornmesser / ESO.
WASP-76b is a hot gas-giant exoplanet located some 640 light-years away in the constellation of Pisces.
Discovered in 2016, the planet orbits the F-type star WASP-76 once every 1.8 days.
WASP-76b is tidally-locked to its star. It takes as long to rotate around its axis as it does to go around the parent star.
On its day side, the planet receives thousands of times more radiation from its star than the Earth does from the Sun.
Its day side temperature climbs above 2,400 degrees Celsius (4,352 degrees Fahrenheit), high enough to vaporize metals. But the night side temperature is much lower — 1,316 degrees Celsius (2,400 degrees Fahrenheit).
“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,” said Professor Ray Jayawardhana, an astronomer in the Department of Astronomy at Cornell University.
In the new study, Professor Jayawardhana and colleagues spotted a rare trio of spectral lines in highly sensitive observations of WASP-76b’s atmosphere.
“We’re seeing so much calcium; it’s a really strong feature,” said Emily Deibert, a doctoral student at the University of Toronto.
“This spectral signature of ionized calcium could indicate that the exoplanet has very strong upper atmosphere winds.”
“Or the atmospheric temperature on the exoplanet is much higher than we thought.”
The team examined the moderate temperature zone of WASP-76b, 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,” Deibert said.
“You can see that the calcium imprint on the spectra is moving quickly along with the planet.”
The findings were published in the Astrophysical Journal Letters.
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Emily K. Deibert et al. 2021. Detection of Ionized Calcium in the Atmosphere of the Ultra-hot Jupiter WASP-76b. ApJL 919, L15; doi: 10.3847/2041-8213/ac2513
