Stefan Pelletier, a doctoral student at iREx, completed his doctoral work at the University of Montreal this fall. Here he summarizes his doctoral research project.
Illustration of the exoplanet WASP-76b, a “hot Jupiter” near its parent star. Intense heat vaporizes rock elements such as magnesium, calcium and iron in the planet’s atmosphere, providing valuable insight into the formation of our solar system. Image credit: Gemini International Observatory/NOIRLab/NSF/AURA/J. da Silva/Spaceengine/M. Zamani
A planet’s atmospheric composition can help us understand its evolution. In fact, scientists have been studying Jupiter and Saturn for decades to understand how they formed. Today it is possible for the first time to examine the composition of distant worlds and to put the planets of the solar system into context. During my doctoral research, I had the opportunity to use various telescopes to study giant gas planets outside our solar system, with the aim of measuring the composition of their atmospheres and using this knowledge to better inform us about how planets form.
As part of my thesis, I demonstrated the capabilities of the SPIRou instrument at the Canada-France-Hawaii Telescope to characterize the atmospheres of exoplanets. By observing the infrared light emitted by the giant exoplanet τ (“Tau”) Boo b, I discovered that its atmosphere is enriched with about the same amount of carbon as Jupiter’s, but is otherwise much drier than expected. This likely indicates that τ Boo b formed in a water-scarce region, much further from its star than where it is today.
Stefan Pelletier, a doctoral student at iREx, speaks at a meeting of the astronomy community. Photo credit: Stefan Pelletier
In another project, I used the MAROON-X instrument on the Gemini North telescope in Hawaii to observe the ultra-hot giant exoplanet WASP-76 b as it passed in front of its parent star. This allowed me to find numerous elements in its atmosphere and measure their abundance. I found that the composition of WASP-76 b is almost identical to that of the star it orbits in many, but not all, elements. These results allowed me to learn more about the chemistry and composition of this giant exoplanet’s clouds.
Finally, I also observed the ultra-hot planet WASP-121 b with the CRIRES+ and ESPRESSO instruments at the European Very Large Telescope in Chile. By analyzing the visible and infrared light captured during these observations, I was able to find elements of ice and rock. By comparing these elements, I was able to determine that WASP-121 b’s atmosphere is composed more of ice than rock. These are restrictions that cannot currently be met on Jupiter and Saturn. Therefore, it is a rare case that studying an exoplanet located hundreds of light-years from Earth allows us to better understand how the giant planets of our own solar system may have formed.
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Stefan completed his doctoral thesis at the University of Montreal between 2019 and 2023 under the supervision of Professor Björn Benneke from iREx. His dissertation will be available soon.