An international team of astronomers reports having identified the presence of ionized calcium in the atmosphere of WASP-76b, a hot Jupiter already known for its extreme environment. The discovery suggests that this exoplanet is even hotter than previously thought. Details of the study are published in The Astrophysical Journal Letters .
WASP-76b is unlike anything in our system. This planet about twenty times larger than Earth orbits its star in just 1.8 days at a distance of about 0.033 AU. Imagine an exoplanet twice the size of Jupiter moving ten times closer to the Sun than Mercury. WASP-76b, found about 640 light-years away of the Earth, thus presents itself as an example of a hot Jupiter .
Because of its proximity to its host star, WASP-76b shows only one side to its star, like the Moon with Earth. On the surface of the "day" side it is approximately 2400°C , is hot enough for molecules to split into atoms and for metals like iron to evaporate into the atmosphere. On the "night" side, it is a little cooler. Temperatures are around 1300°C .
The fact that there are two very different faces also implies the formation of strong winds. A study published a few months ago told us that part of the iron vapor directed towards the atmosphere on the "day" side was sometimes transferred to the other side under the double effect of the rotation of the planet and atmospheric circulation. On the "dark side", these metals then condense before falling back to the ground. The researchers had discovered that this phenomenon only occurs at the day/night boundary, and not at the night/day boundary. Thus, on WASP-76b, it sometimes rains iron, but only in the evening.
A new study led by Cornell University, University of Toronto and Queen's University Belfast today reports the discovery of ionized calcium (an electrically charged version) on the planet. However, according to the authors of this work, the presence of this element suggests a higher atmospheric temperature than previously thought.
The discovery was made in high-resolution spectra obtained with Gemini North near the summit of Mauna Kea in Hawaii. “We see so much calcium. This is a really strong feature “, emphasizes Emily Deibert, lead author of the study.
The new research, which does not speculate on how high the exoplanet's temperatures will be, once again reinforces the idea that the Milky Way is home to a plethora of incredibly diverse worlds, some of which are particularly exotic.
"It is remarkable that we can learn so much about atmospheres, their constituents, their physical properties, the presence of clouds, and even large-scale winds of planets orbiting stars hundreds of light-years away with today’s instruments “, underlines Ray Jayawardhana, dean of Cornell University and co-author of the study. "By remotely sensing dozens of exoplanets spanning a range of masses and temperatures, we will develop a more complete picture of the true diversity of extraterrestrial worlds."
