New Model for the Kreutz Sungrazer System: Contact-Binary Parent and Upgraded Classification of Discrete Fragment Populations

The structure of the Kreutz system of sungrazing comets is shown to be much more complex than formerly believed. Marsden's (1989) division into three subgroups (I, II, IIa) is now greatly expanded, as new evidence is being offered on nine populations of fragments -- I, Ia, II, IIa, III, Pre-I, Pe (side branch of I), IIIa, and IV, incorporating carefully screened data sets from a collection of gravitational orbits for 1500 SOHO/STEREO dwarf Kreutz comets. Tight correlations between the nominal perihelion latitude and nominal longitude of the ascending node are the result of ignored effects of an outgassing-driven acceleration on the orbital motion. The average width of a gap between adjacent populations in the corrected nodal longitude is near 9 deg; the overall range equals 66 deg. A self-consistent model postulates (i) an initial breakup, in general proximity of aphelion, of a contact-binary parent (progenitor) into its two lobes and the neck (originally linking the lobes), giving birth to, respectively, Population I (Lobe I; the main residual mass C/1843 D1), Population II (Lobe II; C/1882 R1), and Population Ia (the neck); followed by (ii) progressive fragmentation of the lobes (primarily Lobe II), mostly (but not exclusively) far from perihelion, giving successively rise to the other populations and clusters of naked-eye Kreutz sungrazers and their debris. The separation velocities were a few meters per second. Massive fragments of Populations Pre-I, IIIa, and IV are yet to be discovered. Relations among the products of cascading fragmentation are depicted in a pedigree chart. The age of the Kreutz system is estimated at two millennia and a mean orbital period of Lobe I and its main residual mass at ~740 yr. The status is reviewed of the possible historical Kreutz comets seen in AD 1106, AD 363, and 372 BC.