Planets form in gas and dust rich circumstellar disks which are leftover from the formation of stars from rotating molecular cloud cores.
Overview
Planets form in gas and dust rich circumstellar disks which are leftover from the formation of stars from rotating molecular cloud cores. On the one hand, this process is simple: small bodies grow into larger ones through collisions (and sticking) of solid particles, or through local gravitational instabilities. On the other hand, the specific outcomes depend on a large number of complex properties requiring coupled understanding of dynamics, chemistry, and radiative transfer over several orders of magnitude in solid particle size, gas density and orbital radius.
The three stages of forming a planet (in our academic opinion)
Our group is engaged in several studies in this area including:
Understanding the thermal history of forming planetesimals and the impact this has on their composition, as well as the role of star forming environment on the distribution of radioactive nuclides (e.g. 26Al and 60Fe). We focus in particular on important elements like C, N, and O. This work is done in collaboration with Tim Lichtenberg (former PhD student at ETH Zürich, now post-doc at Oxford University), Gregor Golabek (U. Bayreuth), Taras Geyras and Maria Schönbächler (ETH Zürich), and Richard Parker (JMLU). Recent references include (Lichtenberg et al., 2016), (Lichtenberg et al., 2016), and (Lichtenberg et al., 2018). The culmination of this work led to Lichtenberg et al. (2019) describing an apparent dichotomy in water content for forming rocky planets. This work is sponsored in part by the ETH Zürich Research Commission as well as the interdisciplinary Swiss planetary science network NCCR PlanetS.
Searching for clues to planet formation processes through multi-wavelength imaging of circumstellar disks in scattered light (e.g. SPHERE on the ESO-VLT) as well as in thermal emission (e.g. with ALMA or NOEMA in millimeter wavelength emission). Recent references include Gratton et al. (2019), Claudi et al. (2019),
Trying to confront theories of gas giant planet formation with observations of forming protoplanets still embedded in circumstellar disks. We focus on transitional disk systems where gaps may have been created due to the forming planet. In systems where gas is still accreting onto the central star we speculate that gas is still interacting with the protoplanet, perhaps leading to accretion shocks and/or the formation of circumplanetary disks. This work is done in collaboration with colleagues at the ETH Zürich as well as the SPHERE GTO Collaboration. Recent references include Sissa et al. (2018), Keppler et al. (2018), Mueller et al. (2018), Szulagyi et al. (2018), Cugno et al. (2019), and Pineda et al. (2019).
Testing the hypothesis that primordial hydrogen-rich atmospheres, which could be accreted by terrestrial planets having formed before the circumstellar gas disk dissipates, could lose enough hydrogen and helium to be habitable through photoevaporation (Howe et al. 2019).
Testing the hypothesis that the gas giant planet mass function can be explained by disk dissipation as a function of host star mass (Adams, Meyer, & Adams, submitted).
How planets are born
How planets are born, a video representation.
References
2018
Impact splash chondrule formation during planetesimal recycling
Tim Lichtenberg, Gregor J. Golabek, Cornelis P. Dullemond, and 3 more authors
@article{2018Icar..302...27L,author={{Lichtenberg}, Tim and {Golabek}, Gregor J. and {Dullemond}, Cornelis P. and {Sch{\"o}nb{\"a}chler}, Maria and {Gerya}, Taras V. and {Meyer}, Michael R.},title={{Impact splash chondrule formation during planetesimal recycling}},journal={\icarus},keywords={Chondrule formation, Meteorites, Planetary formation, Planetesimals, Thermal histories, Astrophysics - Earth and Planetary Astrophysics, Physics - Geophysics},year={2018},month=mar,volume={302},pages={27-43},doi={10.1016/j.icarus.2017.11.004},archiveprefix={arXiv},eprint={1711.02103},primaryclass={astro-ph.EP},adsurl={https://ui.adsabs.harvard.edu/abs/2018Icar..302...27L},adsnote={Provided by the SAO/NASA Astrophysics Data System},}
2016
The effects of short-lived radionuclides and porosity on the early thermo-mechanical evolution of planetesimals
Tim Lichtenberg, Gregor J. Golabek, Taras V. Gerya, and 1 more author
The thermal history and internal structure of chondritic planetesimals, assembled before the giant impact phase of chaotic growth, potentially yield important implications for the final composition and evolution of terrestrial planets. These parameters critically depend on the internal balance of heating versus cooling, which is mostly determined by the presence of short-lived radionuclides (SLRs), such as 26Al and 60Fe, as well as the heat conductivity of the material. The heating by SLRs depends on their initial abundances, the formation time of the planetesimal and its size. It has been argued that the cooling history is determined by the porosity of the granular material, which undergoes dramatic changes via compaction processes and tends to decrease with time. In this study we assess the influence of these parameters on the thermo-mechanical evolution of young planetesimals with both 2D and 3D simulations. Using the code family i2elvis/i3elvis we have run numerous 2D and 3D numerical finite-difference fluid dynamic models with varying planetesimal radius, formation time and initial porosity. Our results indicate that powdery materials lowered the threshold for melting and convection in planetesimals, depending on the amount of SLRs present. A subset of planetesimals retained a powdery surface layer which lowered the thermal conductivity and hindered cooling. The effect of initial porosity was small, however, compared to those of planetesimal size and formation time, which dominated the thermo-mechanical evolution and were the primary factors for the onset of melting and differentiation. We comment on the implications of this work concerning the structure and evolution of these planetesimals, as well as their behavior as possible building blocks of terrestrial planets.
@article{LICHTENBERG2016350,title={The effects of short-lived radionuclides and porosity on the early thermo-mechanical evolution of planetesimals},journal={Icarus},volume={274},pages={350-365},year={2016},issn={0019-1035},doi={https://doi.org/10.1016/j.icarus.2016.03.004},url={https://www.sciencedirect.com/science/article/pii/S001910351600138X},author={Lichtenberg, Tim and Golabek, Gregor J. and Gerya, Taras V. and Meyer, Michael R.},keywords={Planetary formation, Terrestrial planets, Planetesimals, Interiors, Thermal histories}}
Isotopic enrichment of forming planetary systems from supernova pollution
Tim Lichtenberg, Richard J. Parker, and Michael R. Meyer
Monthly Notices of the Royal Astronomical Society, Aug 2016
Heating by short-lived radioisotopes (SLRs) such as 26Al and 60Fe fundamentally shaped the thermal history and interior structure of Solar system planetesimals during the early stages of planetary formation. The subsequent thermo-mechanical evolution, such as internal differentiation or rapid volatile degassing, yields important implications for the final structure, composition and evolution of terrestrial planets. SLR-driven heating in the Solar system is sensitive to the absolute abundance and homogeneity of SLRs within the protoplanetary disc present during the condensation of the first solids. In order to explain the diverse compositions found for extrasolar planets, it is important to understand the distribution of SLRs in active planet formation regions (star clusters) during their first few Myr of evolution. By constraining the range of possible effects, we show how the imprint of SLRs can be extrapolated to exoplanetary systems and derive statistical predictions for the distribution of 26Al and 60Fe based on N-body simulations of typical to large clusters (103–104 stars) with a range of initial conditions. We quantify the pollution of protoplanetary discs by supernova ejecta and show that the likelihood of enrichment levels similar to or higher than the Solar system can vary considerably, depending on the cluster morphology. Furthermore, many enriched systems show an excess in radiogenic heating compared to Solar system levels, which implies that the formation and evolution of planetesimals could vary significantly depending on the birth environment of their host stars.
@article{10.1093/mnras/stw1929,author={Lichtenberg, Tim and Parker, Richard J. and Meyer, Michael R.},title={{Isotopic enrichment of forming planetary systems from supernova pollution}},journal={Monthly Notices of the Royal Astronomical Society},volume={462},number={4},pages={3979-3992},year={2016},month=aug,issn={0035-8711},doi={10.1093/mnras/stw1929},url={https://doi.org/10.1093/mnras/stw1929},eprint={https://academic.oup.com/mnras/article-pdf/462/4/3979/18756772/stw1929.pdf}}
