An international team of astronomers from Cornell University, the University of Toronto, and Queen's University Belfast has detected ionized calcium in the atmosphere of WASP-76b, the ultra-hot Jupiter famed for its extreme conditions. This discovery indicates the exoplanet runs even hotter than previously estimated. Findings are published in The Astrophysical Journal Letters.
WASP-76b has no counterpart in our Solar System. Roughly twice Jupiter's size, it orbits its host star every 1.8 days at just 0.033 AU—imagine Mercury's orbit but ten times closer to the Sun. Located 640 light-years away, WASP-76b exemplifies a hot Jupiter.
Tidally locked like the Moon to Earth, WASP-76b perpetually shows one face to its star. The dayside scorches at approximately 2400°C, hot enough to dissociate molecules and vaporize metals like iron into the atmosphere. The nightside cools slightly to around 1300°C.
Extreme temperature contrasts drive fierce winds. Prior research revealed iron vapors from the dayside carried to the nightside by planetary rotation and atmospheric circulation, where they condense and fall as rain—but only at the evening terminator, not the morning one. On WASP-76b, it literally rains iron in the evenings.
This latest study reports ionized calcium—an electrically charged form—in high-resolution spectra from Gemini North on Mauna Kea, Hawaii. The abundance suggests higher atmospheric temperatures than models predicted, per the research team.
"We see so much calcium. This is a really strong feature," says lead author Emily Deibert.
While exact new temperature estimates await further analysis, the work underscores the Milky Way's vast array of exotic worlds. "It's remarkable that today's instruments let us probe atmospheres, chemistry, clouds, and winds on planets hundreds of light-years away," notes co-author Ray Jayawardhana, dean at Cornell University. "Studying diverse exoplanets will reveal the full spectrum of alien worlds."
