title: Atmospheric characterisation of rocky planets using space-based spectro-photometric observations: From terrestrial exoplanets to lava worlds
Creators: name: Meier Valdés, Erik Andreas
Publisher: name: Universität Bern
Year: 2025
Subjects: subject: 520 Astronomy
subject: 530 Physics

description: The discovery of the first exoplanet orbiting a Sun-like star in 1995 started a fascinating era of discovery and characterisation of faraway worlds. Among the more than 5000 confirmed exoplanets, plenty of them have a rocky composition. Despite their abundance, the atmospheric properties of rocky exoplanets remain poorly constrained. In this thesis we will focus on two particular classes of exoplanets that have drawn interest in recent years: super-Earths and terrestrial worlds orbiting M dwarfs. Among the super-Earths, 55 Cnc e is arguably the most studied one and yet its true nature still remains a mystery, in particular due to variability in the flux. Regarding terrestrial planets orbiting an M dwarf, it is still unclear whether they can harbour an atmosphere or are hot barren rocks. In this work we will focus on the terrestrial exoplanet TOI-1468b. 
In this thesis, the aim is to characterise the atmospheric properties of rocky planets using space-based spectro-photometric observations by CHEOPS, JWST and TESS. ESA’s CHEOPS ultra-high photometric precision presents a unique opportunity to characterise the flux of a super-Earth orbiting a bright Sun-like star in the optical range, while JWST’s precise spectroscopic observations in the infrared can reveal more details about exoplanet atmospheres than any previous space-based telescope.
Here we present photometric observations of 55 Cnc e taken in the optical range by TESS and CHEOPS; and infrared observations of the occultation of TOI-1468b by JWST. We were able to detect the variability in the occultation of 55 Cnc e in the optical range with TESS. Also, with the CHEOPS observations we find variability in the phase modulation of 55 Cnc e occurring on the order of days. Among different mechanisms that could be responsible of 55 Cnc e’s flux variability, we show that the presence of a circumstellar torus of dust is unlikely. The results on the occultation of TOI-1468b with JWST reveal the planet to be hotter than expected and is consistent with an airless bare rock, however the additional source of energy remains unexplained. The complexity in the reduction of JWST observations and dependence of stellar model to produce an emission spectrum shows that additional care has to be taken in the analysis of observations by JWST.
This thesis contributes to the exoplanet science by deepening our understanding of hot rocky exoplanets and their composition, in particular about an iconic super-Earth and a terrestrial world around an M dwarf. It remains to be solved which process, or processes, cause the flux variability on 55 Cnc e. Also, its atmospheric structure is still unclear. These open issues provide motivation for future observing campaigns. TOI-1468b’s apparent lack of atmosphere is a fascinating first result of the JWST Hot Rocks Survey about atmospheres on M-dwarf exoplanets, paving the way for the recently approved STScI initiative allocating 500 hours of JWST time to survey the atmospheres of such planets.