The Role of Ferromagnetic Iron in Planetesimal Formation

• Applicant: Professor Dr. Gerhard Wurm
• Subject Area: Astrophysics and Astronomy
• Term: from 2016 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 320743803

• Final Report Year: 2020

Final Report Abstract

Planetary bodies in the solar system show an iron gradient with iron-rich bodies being closer to the sun. An extreme is Mercury with an iron core well beyond the average planetary core size. There are also a couple of extrasolar planets found which are iron-rich. Hubbard (2014) suggested magnetic erosion as a model to explain selective growth of iron-rich matter. In the magnetic fields of a protoplanetary disk, ferromagnetic material would be harder to fragment and easier to reassemble. We verified this idea in laboratory experiments. While we found that this mechanism does not work at the high energies, we found a magnetic boost in growth at the bouncing barrier, where collisions usually no longer lead to sticking and growth but where particles bounce off each other. The size of particles is increased for (metallic) iron-rich matter in magnetic fields. This magnetic boost sets a bias in particle growth. If this is inherited to later evolutionary phases, this indeed offers a way to explain the formation of iron-rich planets and an iron gradient in planetary systems.

Publications

• Seeding the Formation of Mercurys: An Iron-sensitive Bouncing Barrier in Disk Magnetic Fields, Astrophysical Journal, 869:45 1-6, 2018
  M. Kruss and G. Wurm
  
• Are Pebble Pile Planetesimals Doomed?, Monthly Notices of the Royal Astronomical Society, 484:2779-2785, 2019
  T. Demirci, M. Kruss, J. Teiser, T. Bogdan, F. Jungmann, N. Schneider, and G. Wurm
  
• ARISE: A Granular Matter Experiment on the International Space Station, Review of Scientific Instruments, 90:104503 1-8, 2019
  T. Steinpilz, G. Musiolik, M. Kruss, F. Jungmann, T. Demirci, M. Aderholz, J. E. Kollmer, J. Teiser, T. Bila, E. Guay, and G. Wurm
  
• Constrains on Compound Chondrule Formation from Laboratory High Temperature Collisions, Icarus, 319:133- 139, 2019
  T. Bogdan, J. Teiser, N. Fischer, M. Kruss, and G. Wurm
  
• Composition and Size Dependent Sorting in Preplanetary Growth: Seeding the Formation of Mercury-like Planets, Planetary Science Journal, 1:23 1-6, 2020
  M. Kruss and G. Wurm
  
• Laboratory Impact Splash Experiments to Simulate Asteroid Surfaces, Icarus, 341:113646 1-6, 2020
  T. Bogdan, J. Kollmer, J. Teiser, M. Kruss, and G. Wurm
  
• Wind Erosion on Mars and other Small Terrestrial Planets, Icarus, 337:113438 1-6, 2020
  M. Kruss, G. Musiolik, T. Demirci, G. Wurm, and J. Teiser