2008 Annual Science Report

University of Hawaii, Manoa Reporting  |  JUL 2007 – JUN 2008

Amorphization of Crystalline Water Ice in the Solar System

Project Summary

Our laboratory simulations show that crystalline water ice can never be completely turned into amorphous ice by cosmic rays or solar wind at temperature over 50K. Temperatures of most icy objects in the Solar System, including Jovian satellites, Saturnian satellites, and Kuiper Belt Objects, are equal to or above 50 K; this explains why water ice detected on those objects is mostly crystalline.

4 Institutions
3 Teams
0 Publications
0 Field Sites
Field Sites

Project Progress

We conducted a systematic experimental study to investigate the amorphization of crystalline water ice via ionizing radiation irradiation in the 10-50 K temperature range at doses of up to 140 ± 20 eV per molecule. We found that crystalline water ice can be converted only partially to amorphous ice by electron irradiation. The experiments showed explicitly that a fraction of the 1.65 μm band, which is characteristic for crystalline water ice, survived the irradiation, to a degree that strongly depends on the temperature.

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Quantitative kinetic fits of the temporal evolution of the 1.65 μm band clearly demonstrate for the very first time that there is a balance between thermal recrystallization and irradiation-induced amorphization, with thermal recrystallizaton dominant at higher temperatures. At 50 K, the recrystallization due to thermal effects is strong, and most of the crystalline ice survived. These results have crucial implications to the Solar System. Temperatures of most icy objects in the Solar System, including Jovian satellites, Saturnian satellites, and Kuiper Belt Objects, are equal to or above 50 K; this explains why water ice detected on those objects is mostly crystalline.

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  • PROJECT INVESTIGATORS:
    David Jewitt David Jewitt
    Project Investigator
    Weijun Zheng Weijun Zheng
    Project Investigator
    Ralf Kaiser
    Co-Investigator
  • RELATED OBJECTIVES:
    Objective 2.2
    Outer Solar System exploration