منابع مشابه
Deep Sub-surface Exploration of Cometary Nuclei
The surface regions of cometary nuclei are expected to be extensively modified by cosmic radiation and solar insolation. Induced state changes and associated sublimation and phase-change boundaries are expected to propagate deep into the interior. In the current exploration program a reconnaissance of the highly evolved upper meter of the cometary surface is comprehensively covered. However, th...
متن کاملRotation of Cometary Nuclei
The current understanding of cometary rotation is reviewed from both theoretical and observational perspectives. Rigid-body dynamics for principal axis and non-principal-axis rotators are described in terms of an observer’s point of view. Mechanisms for spin-state changes, corresponding timescales, and spin evolution due to outgassing torques are discussed. Different observational techniques an...
متن کاملStructure and Density of Cometary Nuclei
We are still at a very primitive stage in our understanding of the structure and density of cometary nuclei. Much of the evidence at our disposal is fragmentary and often indirect. Nevertheless, a compelling picture is beginning to emerge of cometary nuclei as collisionally processed fractal aggregates, i.e., rubble piles. The evidence comes from observations of split and disrupted comets, in p...
متن کاملUsing Cometary Activity to Trace the Physical and Chemical Evolution of Cometary Nuclei
Historically, minor bodies are classified as comets based on observations of “activity,” which refers to the appearance of dust and gas around the nucleus. While cometary activity has been observed for centuries, at ever-increasing heliocentric distances, our understanding of the mechanisms for producing cometary activity and its heliocentric dependence has only recently been developed to the l...
متن کاملMorphological Structure and Chemical Composition of Cometary Nuclei and Dust
The chemical composition of comet nuclei derived from current data on interstellar dust ingredients and comet dust and coma molecules are shown to be substantially consistent with each other in both refractory and volatile components. When limited by relative cosmic abundances the water in comet nuclei is constrained to be close to 30% by mass and the refractory to volatile ratio is close to 1:...
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ژورنال
عنوان ژورنال: International Astronomical Union Colloquium
سال: 1991
ISSN: 0252-9211
DOI: 10.1017/s0252921100012719