My research is driven by the exceptional progress taking place in circumstellar disk observations, exoplanet detections, and their characterization. We have recently discovered many exoplanetary systems with architectures significantly different from the Solar System. These discoveries have seriously challenged the classical theory of planet formation. My overarching goal is to understand and describe processes from which planets, particularly the habitable ones, originate.
I have been involved in a range of projects investigating various aspects of the planet formation theory. This page highlights the most important topics of my reserach. You can also see the full list of my scientific publications at ADS or in my ORCiD profile.
Dust coagulation is the initial step toward planet formation. The collisional physics of dust is very complex and requires statistical models. I created an independent implementation of a Monte Carlo algorithm with a representative particle approach. I have also benchmarked the two most popular methods for including dust coagulation, the Monte Carlo algorithm and the Smoluchowski equation solver. During my studies, I have gained significant experience modeling the dust evolution in protoplanetary disks, which allows me to create both toy and advanced numerical models. Recently, I published the pebble predictor, which is a simple method for calculating realistic pebble sizes and fluxes needed in models of planetary growth by pebble accretion.
Dust evolution models are an essential tool to connect theory to observations of circumstellar disks, where planets form. I have been working on implementing dust coagulation into large-scale hydrodynamic codes. Starting during my undergraduate studies, I developed the particle module of Piernik MHD code. Later, in a project led by Tomas Tamfal at the University of Zurich, we included a simplified prescription of dust growth into the RoSSBi code. Recently, in collaboration with the group of Hui Li at the Los Alamos National Laboratory, we included an advanced method, based on the Smoluchowski equation solver, into the LA-COMPASS code.
Planet formation is a journey over many orders of magnitude in size and mass. Going from micron-sized monomers to an Earth-mass planet covers about 40 orders of magnitude in mass. In the Solar System, we still observe some leftovers from the planet formation process, such as the asteroids and comets. In the planet formation theory, such objects are called planetesimals: the first gravitationally bound building blocks of planets. Laboratory experiments and coagulation models find that it is unlikely that dust grows directly to planetesimals. I was one of the first scientists to study the connection between dust coagulation and streaming instability, which is currently the most widely accepted scenario of planetesimal formation. My results support the idea of local planetesimal formation. The water snow line is one of the favorable locations.
The classical theory of planet formation assumed that dust is turned to planetesimals rapidly everywhere in the disk. There were a range of problems related to long timescales of planetesimal accretion and forming the cores of giant planets before the gas disk dispersed. At the same time, models of terrestrial planet accretion needed Jupiter and its migration to solve the so-called "small Mars problem". My research shows that planetesimal formation only happens at some locations in the protoplanetary disks, in particular around the water snow line. Planetesimals do not form all at once, but rather in two bursts and the first burst takes place very early, during the formation of the Sun. In the Science paper led by Tim Lichtenberg, we connected astrophysical and geophysical models to meteorites studies and showed this planetesimal formation scenario reproduces the present-day Solar System.
Mark A. Garlick / markgarlick.com