Cometary dust: structure at the nanometre scale

Abstract : The Rosetta orbiter carried three dedicated dust analysis instruments to investigate the properties of the comet andits dust at smallest scales. The images with the highest resolutions were obtained by the MIDAS (Micro-ImagingDust Analysis System) atomic force microscope [1,2]. It collected dust particles of one to tens of micrometresin size and imaged their surface in 3D. Nominal images had approximately hundreds of nanometres resolutionand were used to study the particle morphology at the micrometre scale. It was shown that the majority ofcollected particles were fragile agglomerates [3] with a moderate packing density of subunits at the surface [4].Exceptions were one extremely porous particle with a fractal structure that is suggested to be pristinely preservedfrom early agglomeration processes in our Solar System [4], and the particles of about one micrometre size thatshow less fragility. To study these smallest detected particles a special scanning mode, called ‘reverse imagingmode‘, was developed that reached resolutions down to eight nanometres [5]. In the reverse imaging mode dustparticles were picked up with the tip and imaged with the help of a sharp spike on a calibration sample. Theresulting images opened the possibility to identify the agglomerate structure of the dust down to the nanometrescale and to determine smallest features with mean sizes of about 100 nanometres. Whether these smallestfeatures are surface related or true subunits comprising the dust will be discussed on the basis of comparisons tosmallest subunit sizes identified by indirect Rosetta measurements and by investigations of other cometary material.References:[1] W. Riedler, K. Torkar, H. Jeszenszky, et al., MIDAS – The Micro-Imaging Dust Analysis System for theRosetta Mission. Space Science Reviews 128, 2007.[2] M.S. Bentley, H. Arends, B. Butler, et al., MIDAS: Lessons learned from the first spaceborne atomic forcemicroscope. Acta Astronautica 125, 2016.[3] M.S. Bentley, R. Schmied, T. Mannel et al., Aggregate dust particles at comet 67P/Chruyumov-Gerasimenko,Nature, 537, 2016.[4] T. Mannel, M.S. Bentley, R. Schmied et al., Fractal cometary dust – a window into the early Solar system,MNRAS, 462, 2016.[5] T. Mannel, M.S. Bentley, P.D. Boakes, et al., MIDAS results: classification and extension to the nanometrescale, submitted to Astronomy & Astrophysics, Rosetta special issue, 2018.
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Thurid Mannel, Mark Bentley, Peter Boakes, Harald Jeszenszky, Pascale Ehrenfreund, et al.. Cometary dust: structure at the nanometre scale. EGU General Assembly 2019, Apr 2019, Vienna, Austria. pp.EGU2019-17361. ⟨insu-02062955⟩

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