PLANETARY SCIENCE: An Isotopic View of the Early Solar System

Comets are believed to have preserved pristine material from the early stages of the Solar System formation, thus providing unique information on intricate processes like dust growth mechanisms. The Rosetta mission gave us the best opportunity to investigate nearly pristine cometary dust particles of comet 67P/Churyumov&#8211;Gerasimenko. Among the three in-situ dust instruments, the MIDAS (Micro-Imaging Dust Analysis System) atomic force microscope collected cometary dust particles with sizes from hundreds of nanometres to tens of micrometres and recorded their 3D topography, size, shape, morphology, and related parameters [1]. MIDAS collected dust emitted from comet 67P on dedicated targets. Particles fell through the entry funnel and collided with the collection targets [2] causing an unknown degree of particle alteration. To understand which structural properties of the dust remained pristine and can be used to understand comets and early Solar System processes it is important to understand the collection alteration. Dedicated laboratory experiments were carried out by previous studies [3, 4]. They found that the degree of alteration upon collection is strongly determined by the particle size, strength, and the collection velocity. They indicate that particles in the MIDAS size range deposited with moderate velocities about less than a few metres per second can stick on a target without major alteration. We aim to determine the structurally least altered MIDAS particles and investigate their properties. As database we use an improved version of the MIDAS particle catalogue [5]. Selecting all particles suitable for our analysis (e.g., cometary origin, sufficiently high image quality) grants us topographic data of over 600 nano- to micrometre-sized dust particles of comet 67P. We create dust coverage maps showing the distribution of the selected dust particles on the collection targets. As first, simple classification we divide the particles into those detected in clusters, suggested to be fragments originating in a shattering event of one large parent particle, and those remote from others that are potentially individually collected particles. Finally, we&#160;use a shape descriptor to categorise the particles according to their characteristics, e.g., shape and size, and compare to previous results from COSIMA [6] and simulation/laboratory studies [3, 7]. &#160; [1] Bentley, M.S., Schmied, R., Mannel, T., et al. 2016, Nature, 537 [2] Bentley, M. S., Arends, H., Butler, B., et al. 2016, Acta Astronautica, 125, 11 [3] Ellerbroek, L. E., Gundlach, B., Landeck, A., et al. 2017, MNRAS, 469, S204 [4] Ellerbroek, L. E., Gundlach, B., Landeck, A., et al. 2019, MNRAS, 486, S3755 [5] Boakes, P., and the MIDAS team, 2018. &#8216;MIDAS Particle Catalogue&#8217;. ESA Planetary Science Archive&#160;&#160;Dataset: RO-C-MIDAS-5-PRL-TO-EXT3-V2.0. Product ID: RO-C-MIDAS-5-PRL-TO-EXT3-V2.0 [6] Langevin, Y., Hilchenbach, M., Ligier, N., et al. 2016, Icarus, 271, 76 [7] Lasue, J., Maroger, I., Botet, R., et al. 2019, A&A, 630,

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Condensation Calculations in Planetary Science and Cosmochemistry

Oxford Research Encyclopedia of Planetary Science ◽

10.1093/acrefore/9780190647926.013.201 ◽

2021 ◽

Author(s):

Denton S. Ebel

Keyword(s):

Solar System ◽

Total Pressure ◽

General Circulation ◽

Local Equilibrium ◽

Circulation Model ◽

Planetary Science ◽

Physical Models ◽

Early Solar System ◽

Disk Model ◽

Distribution Of Elements

The Sun’s chemical and isotopic composition records the composition of the solar nebula from which the planets formed. If a piece of the Sun is cooled to 1,000 K at 1 mbar total pressure, a mineral assemblage is produced that is consistent with the minerals found in the least equilibrated (most chemically heterogeneous), oldest, and compositionally Sunlike (chondritic), hence most “primitive,” meteorites. This is an equilibrium or fractional condensation experiment. The result can be simulated by calculations using equations of state for hundreds of gaseous molecules, condensed mineral solids, and silicate liquids, the products of a century of experimental measurements and recent theoretical studies. Such calculations have revolutionized our understanding of the chemistry of the cosmos. The mid-20th century realization that meteorites are fossil records of the early solar system made chemistry central to understanding the origin of the Earth, Moon, and other bodies. Thus “condensation,” more generally the distribution of elements and isotopes between vapor and condensed solids and/or liquids at or approaching chemical equilibrium, came to deeply inform discussion of how meteoritic and cometary compositions bear on the origins of atmospheres and oceans and the differences in composition among the planets. This expansion of thinking has had profound effects upon our thinking about the origin and evolution of Earth and the other worlds of our solar system. Condensation calculations have also been more broadly applied to protoplanetary disks around young stars, to the mineral “rain” of mineral grains expected to form in cool dwarf star atmospheres, to the expanding circumstellar envelopes of giant stars, to the vapor plumes expected to form in giant planetary impacts, and to the chemically and isotopically distinct “shells” computed and observed to exist in supernovae. The beauty of equilibrium condensation calculations is that the distribution of elements between gaseous molecules, solids, and liquids is fixed by temperature, total pressure, and the overall elemental composition of the system. As with all sophisticated calculations, there are inherent caveats, subtleties, and computational difficulties. In particular, local equilibrium chemistry has yet to be consistently integrated into gridded, dynamical astrophysical simulations so that effects like the blocking of light and heat by grains (opacity), absorption and re-emission of light by grains (radiative transfer), and buffering of heat by grain evaporation/condensation are fed back into the physics at each node or instance of a gridded calculation over time. A deeper integration of thermochemical computations of chemistry with physical models makes the prospect of a general protoplanetary disk model as hopeful in the 2020s as a general circulation model for global climate may have been in the early 1970s.

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Laboratory and in-situ analysis of comet dust

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100102122 ◽

1988 ◽

Vol 46 ◽

pp. 8-9

Author(s):

D.E. Brownlee ◽

A.L. Albee

Keyword(s):

Electron Microscopy ◽

Solar System ◽

Laboratory Study ◽

Isotopic Analysis ◽

Building Blocks ◽

Sem Analysis ◽

Early Solar System ◽

Cometary Material ◽

Comet Dust

Comets are primitive, kilometer-sized bodies that formed in the outer regions of the solar system. Composed of ice and dust, comets are generally believed to be relic building blocks of the outer solar system that have been preserved at cryogenic temperatures since the formation of the Sun and planets. The analysis of cometary material is particularly important because the properties of cometary material provide direct information on the processes and environments that formed and influenced solid matter both in the early solar system and in the interstellar environments that preceded it.The first direct analyses of proven comet dust were made during the Soviet and European spacecraft encounters with Comet Halley in 1986. These missions carried time-of-flight mass spectrometers that measured mass spectra of individual micron and smaller particles. The Halley measurements were semi-quantitative but they showed that comet dust is a complex fine-grained mixture of silicates and organic material. A full understanding of comet dust will require detailed morphological, mineralogical, elemental and isotopic analysis at the finest possible scale. Electron microscopy and related microbeam techniques will play key roles in the analysis. The present and future of electron microscopy of comet samples involves laboratory study of micrometeorites collected in the stratosphere, in-situ SEM analysis of particles collected at a comet and laboratory study of samples collected from a comet and returned to the Earth for detailed study.

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