Nano-analysis of cometary dust - uncovering the building blocks of the Solar System

The Rosetta mission is one of the most exciting space missions of our time. Rosetta made history in August 2014 by rendezvousing with comet 67P/ChuryumovGerasimenko after 10 years in flight and has already spectacularly delivered the lander Philae to the comet`s surface in November 2014. Although the mission is only just beginning it already returned a wealth of stunning imagery and scientific data. Until at least the end of 2015 Rosetta will follow the comet as it makes its closest approach to the Sun. In the end, Rosetta and Philae will have revolutionised cometary science. On-board Rosetta is a unique instrument called MIDAS which collects the smallest cometary dust grains and analyses them with an Atomic Force Microscope: A sharp tip scans the surface of the grains and produces three dimensional images with a resolution of several nanometres that is 1000 times smaller than a human hair! As some of the most primitive bodies in the Solar System, comets are believed to contain material that is relatively unchanged since the formation of the Sun and planets. Nano-analysis of this material will offer new insights into how comets, and the rest of the Solar System, were built. The three dimensional images produced by MIDAS will address a range of questions in cometary science from a new perspective. This project will use these data to derive statistical properties of cometary dust, including size, shape, porosity and the fraction that are aggregates versus compact particles. The surface features of the dust grains will be studied to determine their building blocks. A special working mode, Magnetic Force Microscopy, will be used to identify grains with magnetic minerals and could even constrain the strength of magnetic fields in the early Solar System. MIDAS data analysis also addresses the evolution of dust after its release from the comet, in particular the size distribution of the smallest particles and the fragmentation mechanisms of cometary dust. To fully exploit the data from the MIDAS instrument, novel data analysis techniques will be developed. As Rosetta is still active in the beginning of the 3 year project and as the applicant is the Principal Investigator of MIDAS, it will be possible to perform specific collection campaigns and scans to expand the already existing data set. The project will fund one PhD student who will join the MIDAS team at the Space Research Institute in Graz and have the opportunity do novel science as part of one of the most exciting planetary science missions of our time.

How did our solar system form? Although we already understood the basics, there are still many unanswered questions. This project studied how the smallest dust particles, circling in a mix of dust and gas around the early Sun, evolved to larger and larger structures to ultimately build the nowadays known bodies like comets, moons, and planets. Particularly interesting for this project were the comets as they kept material from the early solar system in a nearly pristine state until today. ESA carried out the exciting Rosetta comet mission between 2014 and 2016. For the first time ever a comet was accompanied on his way around Sun. Comet 67P/Churyumov-Gerasimenko was thoroughly investigated, amongst others by MIDAS, an atomic force microscope particularly designed to study the smallest cometary dust particles. The instrument was leadingly built and operated at the Space Research Institute of the Austrian Academy of Sciences in Graz. MIDAS collected micrometre-sized dust particles - dust so small that it is barely visible with naked eye - and imaged them in 3D. This project investigated the structures of the imaged dust particles and how they evolved in the early solar system. A first remarkable result of this project showed that all dust particles are assembled of smaller particles that are again made of smaller entities. This hierarchical structure starts with the fundamental building blocks of roughly 100nm size, which is about the size of viruses. Via analyses of the dust structures, it was possible to trace how the fundamental building blocks clustered and grew to extremely porous, long-chained particles. When these porous 'dust bunnies' reached sizes of centimetres, they started to bump into each other. Those collisions lead to more compact, about millimetre-sized particles named 'pebbles'. Through collaboration with many cometary scientists, it was possible to determine how comets were built out of the compacted pebbles and the not (completely) compacted porous particles. Using MIDAS data, this project could determine the fundamental building blocks, the porous 'dust bunnies', and fragments of the compacted 'pebbles'. Dust particles from the early solar system in different evolutionary stages were investigated and their growth path reconstructed. Additionally, many interesting dust particle properties were determined as, e.g., the hardness of the fundamental building blocks or their shape reminiscent of potatoes. In the future, the results of this project will help to further our understanding of comets and to develop more sophisticated evolutionary theories of our solar system.