Spectrum reveals extreme exoplanet is even more exotic


By Blaine Friedlander, with notes from Meaghan MacSween


Artist’s impression of a hot Jupiter exoplanet. Credit: ESO.

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.

Artist’s impression of the extreme atmosphere of WASP-76b. Credit: ESO.

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.

Star trails over Gemini North. Credit: Gemini Observatory/AURA.

“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.”


The ExoGemS survey – intended to study 30 or more planets – is led by Jake Turner, a Carl Sagan Fellow in NASA’s Hubble Fellowship program, who is in Cornell’s Department of Astronomy (A&S) and is also advised by Jayawardhana. Other authors on the paper, “Detection of Ionized Calcium in the Atmosphere of the Ultra-Hot Jupiter WASP-76b,” include Ernst J. W. de Mooij of the Queen’s University Belfast; Luca Fossati of the Austrian Academy of Sciences; Callie E. Hood and Jonathan J. Fortney, both from University of California, Santa Cruz; Romain Allart of the University of Montreal; and David K. Sing of Johns Hopkins University. Cornellians included researchers Andrew Ridden-Harper and Laura Flagg, both in Jayawardhana’s group, and Ryan MacDonald. Portions of this research were funded by NASA.


Emily Deibert is supported by a Vanier Canada Graduate Scholarship – NSERC. She is also co-supervised by Suresh Sivanandam, Associate Professor at the Dunlap Institute.


For more information on this story, please contact:
Blaine Friedlander



To connect with Emily Deibert, please contact:
Meaghan MacSween
Communications and Multimedia Officer
Dunlap Institute for Astronomy & Astrophysics,
University of Toronto


The Dunlap Institute for Astronomy & Astrophysics at the University of Toronto is an endowed research institute with more than 90 faculty, postdocs, students and staff, dedicated to innovative technology, ground-breaking research, world-class training, and public engagement. The research themes of its faculty and Dunlap Fellows span the Universe and include: optical, infrared and radio instrumentation; Dark Energy; large-scale structure; the Cosmic Microwave Background; the interstellar medium; galaxy evolution; cosmic magnetism; and time-domain science. The Dunlap Institute for Astronomy and Astrophysics, David A. Department of Astronomy & Astrophysics and the Canadian Institute for Theoretical Astrophysics comprise the leading centre for astronomical research in Canada, at the leading research university in the country, the University of Toronto.