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With those of the mainstream grains (Fig. 5) except for the sub-population of the nova grains (Amari et al. 2001c Nittler and Hoppe 2005) which plot to the 30Si-rich side of the Si mainstream line. Besides novae for grains with very large 15N excesses, J-type carbon stars and born-again AGB stars have been proposed as potential stellar sources for the type A and B grains. Both types of stars are poorly understood at present. SiC X grains are very rare (about 1 of all presolar SiC grains). By...

DH Wooden

Originally published in the journal Space Science Reviews, Volume 138, Nos 1-4. DOI 10.1007 s11214-008-9424-2 Springer Science+Business Media B.V. 2008 Abstract Comets are heterogeneous mixtures of interstellar and nebular materials. The degree of mixing of interstellar sources and nebular sources at different nuclear size scales holds the promise of revealing how cometary particles, cometesimals, and cometary nuclei accreted. We can ascribe cometary materials to interstellar and nebular...

Origins of Cometary Materials

Comet Size Distribution

Originally published in the journal Space Science Reviews, Volume 138, Nos 1-4. DOI 10.1007 s11214-007-9299-7 Springer Science+Business Media B.V. 2008 Abstract In this introductory presentation, material is categorized according to our state of knowledge What do we know, what do we think we know but don't know certainly, and what do we not know but often describe it as if it were a well-established fact about comets, their nuclei, their composition, and processes within comets and their...

Discussion Interstellar Molecules in Comets

The cometary characteristics discussed here, when taken individually, present a puzzling picture and appear to indicate that comets contain materials from very different chemical Fig. 6 Equilibrium ortho para ratios in water, ammonia and formaldehyde as a function of temperature. The observed values are plotted for water and ammonia in ten comets. In two cases, the water OPR is gt 3, larger than the equilibrium ratio at any temperature. However, the error bars on these measurements are...

Introduction

Comet dust grain properties provide insights into physical conditions and processes in our protoplanetary disk, not only in the regions where nuclei accreted but also in the warmer regions of the disk inside the water snow line. The insights arise when we undertake four ventures 1 distinguish between 'interstellar' and 'nebular' sources for cometary refractory grains 2 identify the presence of cometary-like refractory grains in chondritic asteroidal materials 3 understand in detail how...