Planet Formation


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.

Our group is engaged in several studies in this area including:

1. 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. (2016a), Lichtenberg et al. (2016b), 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.

2. 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),

3. 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).

4.  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).

5.  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).