Processing of Cometary Nuclei by Cosmic Rays
Abstract
Comets are considered as mostly unaltered samples of the proto-solar nebula containing the most pristine material of the solar system. However, they are constantly bombarded by particles like the Galactic Cosmic Rays (GCRs) and solar particles (the solar wind and more energetic particles from solar eruptions). We model the energy deposition of cosmic rays as a function of depth using a Geant4 application modified to account for the isotope creation process and use results from laboratory experiments to assess the impact of this energy deposition on cometary nuclei. We show that only GCR are energetic enough and deposit energy over long enough time periods to significantly alter the nucleus in depth. We show that GCRs do not significantly modify the isotopic composition of cometary material. However, they significantly change its chemical composition down to depths of the order of several tens of meters. Furthermore, cosmic rays alter the cometary ice structure in the first tens of meters inside the nucleus, turning it into compact amorphous ice regardless of the initial type of ice. A consequence of comet irradiation is that the outer part of their nucleus cannot be considered as pristine solar nebula material. It also implies that dynamically `new' comets, i.e. comets that have entered the solar system recently, should release material with different composition and flux compared to dynamically `old´ comets shedding unprocessed material from the inner part of their nuclei, as they lost their altered outer layers on previous perihelion passes.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.P54A..04M
- Keywords:
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- 5109 Magnetic and electrical properties;
- PHYSICAL PROPERTIES OF ROCKS;
- 5194 Instruments and techniques;
- PHYSICAL PROPERTIES OF ROCKS;
- 6297 Instruments and techniques;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS;
- 6969 Remote sensing;
- RADIO SCIENCE