Earth's 2006 encounter with comet 73P/Schwassmann-Wachmann: Products of nucleus fragmentation seen in closeup

Abstract

Abstract. The large numbers of nucleus fragments observed are a spectacular illustration of the process of cascading fragmentation in progress, a concept introduced to interpret the properties of the Kreutz system of sungrazers and comet D/1993 F2. The objective is to describe the fragmentation sequence and hierarchy of comet 73P, the nature of the fragmentation process and observed events, and the expected future evolution of this comet. The orbital arc populated by the fragments refers to an interval of 3.74 days in the perihelion time. This result suggests that they all could be products (but not necessarily first-generation fragments) of two 1995 events, in early September (involving an enormous outburst) and at the beginning of November. The interval of perihelion times is equivalent to a range of about 2.5 m/s in separation velocity or 0.00012 the Sun's attraction in nongravitational deceleration. Their combined effect suggests minor orbital momentum changes acquired during fragmentation and decelerations compatible with survival over two revolutions about the Sun. Fragment B is a likely first-generation product of one of the 1995 events. From the behavior of the primary fragment C, 73P is not a dying comet, even though fragment B and others were episodically breaking up into many pieces. Each episode began with the sudden appearance of a starlike nucleus condensation and a rapidly expanding outburst, followed by a development of jets, and a gradual tailward extension of the fading condensation, until the discrete masses embedded in it could be resolved. In April-May, this debris traveled first to the southwest, but models show their eventual motion toward the projected orbit. Fainter fragments were imaged over limited time, apparently because of their erratic activity (interspersed with periods of dormancy) rather than improptu disintegration. A dust trail joining the fragments and reminiscent of comet 141P/Machholz suggests that cascading fragmentation exerts itself profoundly over an extremely broad mass range of particulate debris.

2006 Fragmentation of Comet 73P/Schwassmann-Wachmann 3B observed with Subaru/Suprime-Cam

“…Similar evidence was found for the broken comet C/1999 S4 (LINEAR): Weaver et al (2001) estimated the separation time from the dynamical properties of 100-m mini-fragments and found that their results indicated an earlier time than the commonly accepted disruption time of C/LINEAR. In addition to the outburst on 1 April, Sekanina (2007) argued that successive outbursts occurred on 24 April and 2 May, although, in Fig. 8, we cannot find evidence for an outburst on 24 April.…”

“…Therefore, we can argue that most of minicomets in the southwest were released by an outburst occurring in late March or early April. The onset time of 26 March is earlier than the generally described outburst time of 1 April (Sekanina, 2007). This small discrepancy may imply that these mini-fragments were active and progressive during the early stage of the ejection and became inactive over a one-month period.…”

“…We found that the stellar profile was similar to the (3 May). 1, 2, and 3 denote the times of the three outbursts described by Sekanina (2007). The solid line was obtained by fitting the data between À150 days and À65 days before the perihelion passage, H D = 12.7 + 15.0 log10(r h ).…”

The Volatile Composition of the Split Ecliptic comet 73P/Schwassmann-Wachmann 3: A Comparison of Fragments C and B

“…In 1995 while reaching perihelion, SW3 brightened greatly between September 5 and 8 (Crovisier et al 1996), and the first breakup occurred approximately 6 weeks later (Sekanina 1996). Three brightness condensations were found (Boenhardt & Kaufl 1995) in images taken on December 12-13, and several others were found thereafter.…”

Coma morphology of Jupiter-family comets

“…The 2006/2007 apparition was particularly favorable, however, because the comet approached to within 0.08 AU of the Earth when it was near perihelion. During this encounter, the comet was observed to experience multiple cascading fragmentation events (Sekanina, 2007), which were observed by numerous observers worldwide. These observations will provide useful information about the exposure of fresh material, as well as providing constraints on the size distribution of the cometesimals that comprised the nucleus, and the dynamics involved in their breakup.…”