CO2-ice in the context of planet formation

• Applicant: Dr. Jens Teiser
• Subject Area: Astrophysics and Astronomy
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 413220058

The process of planet formation begins with the coagulation of solids from micrometer size dust grains. Typically, growth of silicate aggregates is efficient at first, but stalls at an agglomerate sizes of few millimeters to centimeter, as here agglomerates rather bounce off each other than stick together. Protoplanetary disks show a temperature gradient with higher temperatures close to the star and cooler regions further out. At a certain distance, the so-called snowline, water ice begins to form. Due to its polar structure, water ice grains stick more efficiently together than silicates. Water ice agglomerates are expected to grow to larger sizes as the sticking behavior favors growth. Further out in the protoplanetary disk temperatures drop further, so other ice species are present. Here, CO and CO2 are the most important species. More refractive materials form the condensation seed for the more volatile materials, so the surface of particles is dominated by the most volatile species, which is present as solid material. The CO2-iceline forms therefore marks the outer boundary of the region, where collisions are dominated by the surface properties of water ice. Although first studies with CO2-ice exist, a systematic study is still missing and only a very distinct set of parameters (agglomerate sizes and velocities) has been investigated so far.The goal of the proposed project is to investigate the collision behavior of CO2-ice agglomerates in a wide range of agglomerate sizes (< 100 µm – few cm) and collision velocities (few cm/s – 7 m/s). With these experiments the self-consistent growth of CO2-agglomerates and the corresponding evolution of their porosity will be studied. The parameter range of the proposed experiments will cover the complete range of collision results, from sticking, bouncing, growth via mass transfer to erosion and total destruction of target bodies, finally. While this database will be suitable to include CO2-collisions in disk models, additional experiments will be performed to measure the contact forces between CO2-grains.

• DFG Programme: Research Grants