Billion stars, trillion planets. Exploring the properties of exoplanets and multi-planetary systems

Licentiate thesis, 2025

Over the past 30 years, exoplanetary science has expanded enormously,

leading to amazing discoveries and new fascinating insight. Technological

advancements, including ground- and space-based missions, have enabled

the detection and characterization of more than 5800 planets beyond the

Solar System.

In this thesis, I provide a brief overview of the exoplanet field, in particular

the observed population of exoplanets and multi-planetary systems.

I also describe our current methods of detecting exoplanets, focusing primarily

on the transit photometry and the radial velocity techniques since

they are the two most successful methods thus far. However, there are

specific challenges and detection biases associated with these methods,

some of which are outlined in this thesis.

Furthermore, I present two of the most astonishing and important

discoveries in astronomy: the ubiquity and rich diversity of exoplanets.

Surprisingly, approximately every star is estimated to host at least one

planet, and we have detected many different types of planets, most of

which have sizes between those of Earth and Neptune.

Remarkably, nearly half of the confirmed exoplanets have been found

in multi-planetary systems, resulting in more than 970 such systems,

most of which are in compact configurations. This thesis reviews the

properties and architectures of the multi-planetary systems as well as the

similarities frequently exhibited within these systems: Planets orbiting

the same star tend to have equal sizes and masses and be regularly spaced

in nearly circular and coplanar orbits. These intra-system similarities are

further discussed in my paper, which is summarized and included in this

thesis. The paper presents my recent work in which I examined all the

systems with minimum three confirmed planets, focusing on their sizes,

masses, and orbital spacings.

Our current and future missions will enhance our knowledge of exoplanets,

including their formation and evolution, and help us determine

their underlying properties and demographics.