Qualitative and quantitative study of known exoplanets and exoplanetary systems

The number of discovered exoplanets reached five thousand, and it allows scientists to look not only at individual planets’ occurrence trends but start to analyse multi-planet systems in a statistical sense. In this thesis, I focused on studying the systems with at least two planets, of which the fundamental parameters are well known from observations. The goals were (1) to begin drawing the first conclusions about what the internal structure of such planets might be and (2) to find how exoplanetary system architecture can be compared with that of the solar system. For the research purposes, I developed a routine that "weights" the data points according to the measurement precision to fully accommodate the errors of the different parameters, and it allowed me to statistically assess a larger sample than in previous studies. Assessing this study's sample, I inferred new empirical exoplanet's mass-radius relations for the rocky and volatile-rich populations, with the major challenge of both populations occupying a similar region of the M-R diagram. To distinguish them, I used the 100%H2O EOS line and, sequentially, 3300 kg m-3 bulk density cut-off. While these results for both population and the two regimes are in agreement with previous studies, they indicate that at a certain mass the planet could have a variety of radii due to a larger number of different interior structures and compositions. Investigating "peas in a pod" patterns in exoplanet's system architecture, I found similarities in sizes and bulk densities of adjacent planets, but not in masses and period ratios. However, some systems show a better correlation than others, and it can be contributed to a certain stellar parameter and its range as the solar age for radii, the low Teff for masses, and the solar metallicity for densities. The small cool star systems also have overall well-correlated planet pairs. Exploring spacing and packing trends in multi-planet systems, I found that first-order and second-order orbital resonances attract planet pairs in the sample. If the average radii or masses of planets pairs are small, the period ratios also tend to be small, and the greater variety in period ratios arises with larger average radii. Small stars have small planets loosely packed dynamically, while the larger stars can have bigger tightly packed planets, with many systems in the sample showing completeness. My findings show that this study sample differs from the solar system characteristics and mostly represents closely-packed hot super-Earths and mini-Neptunes rich systems. Also, some parameters of the sample planets are showing certain patterns and similarities in the system architecture that do not exist among planets around the Sun