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Micrometer-sized Water Ice Particles for Planetary Science Experiments: Influence of Surface Structure on Collisional Properties

Gärtner, S.; Gundlach, B.; Headen, T. F.; Ratte, J.; Oesert, J.; Gorb, S. N.; Youngs, T. G. A.; Bowron, D. T.; Blum, J. and Fraser, H. J. (2017). Micrometer-sized Water Ice Particles for Planetary Science Experiments: Influence of Surface Structure on Collisional Properties. The Astrophysical Journal, 848(2), article no. 96.

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Models and observations suggest that ice-particle aggregation at and beyond the snowline dominates the earliest stages of planet formation, which therefore is subject to many laboratory studies. However, the pressure–temperature gradients in protoplanetary disks mean that the ices are constantly processed, undergoing phase changes between different solid phases and the gas phase. Open questions remain as to whether the properties of the icy particles themselves dictate collision outcomes and therefore how effectively collision experiments reproduce conditions in protoplanetary environments. Previous experiments often yielded apparently contradictory results on collision outcomes, only agreeing in a temperature dependence setting in above ≈210 K. By exploiting the unique capabilities of the NIMROD neutron scattering instrument, we characterized the bulk and surface structure of icy particles used in collision experiments, and studied how these structures alter as a function of temperature at a constant pressure of around 30 mbar. Our icy grains, formed under liquid nitrogen, undergo changes in the crystalline ice-phase, sublimation, sintering and surface pre-melting as they are heated from 103 to 247 K. An increase in the thickness of the diffuse surface layer from ≈10 to ≈30 Å (≈2.5 to 12 bilayers) proves increased molecular mobility at temperatures above ≈210 K. Because none of the other changes tie-in with the temperature trends in collisional outcomes, we conclude that the surface pre-melting phenomenon plays a key role in collision experiments at these temperatures. Consequently, the pressure–temperature environment, may have a larger influence on collision outcomes than previously thought.

Item Type: Journal Item
Copyright Holders: 2017 The American Astronomical Society
ISSN: 1538-4357
Project Funding Details:
Funded Project NameProject IDFunding Body
Not SetNot SetThe Open University (OU)
Linking Solid-State Astronomical Observations and Gas-Grain Models to Laboratory DataST/M007790/1STFC (Science & Technology Facilities Council)
(Aurora Project) Icy Grain Aggregation: Building Comets and Asteroids as a Harbour for Pre-Biotic ChemistryST/M003051/1UK Space Agency (UKSA)
60 Second Adventures in MicrogravityST/N006488/1UKSA UK Space Agency
Science in the StadiumST/N005775/1STFC (Science & Technology Facilities Council)
Not SetST/ L000776/1STFC (Science & Technology Facilities Council)
International Exchange AwardIE/14/3Royal Society
Keywords: accretion, accretion disks; methods: laboratory: solid state; planets and satellites: formation
Academic Unit/School: Faculty of Science, Technology, Engineering and Mathematics (STEM) > Physical Sciences
Faculty of Science, Technology, Engineering and Mathematics (STEM)
Item ID: 54982
Depositing User: ORO Import
Date Deposited: 09 May 2018 10:38
Last Modified: 03 May 2019 11:07
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