Planetary and stellar composition
Determining the internal structure of exoplanets is essential to obtain its composition and its surface conditions, which enable us to know if the planet is habitable.
Water is one of the most abundant volatiles that can be found in planetary bodies.
Depending on the surface conditions of the planet, water can be in a liquid, ice, or vapour phases, which present very different densities.
Thus, it is required to take into account these different phases with equations of state and pressure-temperature profiles that are valid under planetary interior conditions.
In addition, it is necessary to treat data from mass, radius and stellar chemical composition with a Bayesian approach to infer the most likely ratios of volatiles and silicates that form an exoplanet.
These are the two topics I’m currently working on in my PhD, whose latest results can be seen in Acuña et al. 2021.
The chemical composition of the host star, particularly the Fe and Si abundances, can be used to constrain the bulk composition of its exoplanet.
Furthermore, planet formation might also affect the composition on the host star.
Meléndez et al. 2009 proposed that stars harbouring rocky planets could present less refractory elements in their photospheres than stars without planets.
This difference in chemical composition was very subtle, and required a detailed and precise chemical analysis of different rocky planet hosts.
This was the motivation of my master thesis, in which I conducted a line-by-line, differential chemical analysis of a sample of planet hosts.
My results confirmed that the Sun is depleted in refractory elements compared to solar twins without exoplanets.
However, the other planet hosts in my sample were very diverse in chemical composition.
This diversity has been later confirmed with a greater sample of stars by Liu et al. 2020.
Exoplanets with extended atmospheres are favourable targets for transmission spectroscopy.
With this technique, we can detect spectral features from the exoplanet’s atmosphere, such as a slope at short visible wavelengths caused by Rayleigh scattering.
However, if clouds form in the atmosphere, they will absorb most of the radiation coming from the star and the transmission spectrum will be flat with no spectral features.
During my internship in the European Space Agency (ESA), I worked on a pipeline to reduce and analyse observational data from transmission spectroscopy of a sample of hot Jupiters.
As a result, I obtained the transmission spectrum of one hot Jupiter, WASP-74 b, that presents a Rayleigh slope at short wavelengths, concluding that its atmosphere is at least partially clear.
This was presented in a poster session at the ARIEL 2020 conference.