A dynamical analysis of the dust tail of Comet C/1995 O1 (Hale–Bopp) at high heliocentric distances

Abstract

Comet C/1995 O1 (Hale-Bopp) has provided an unprecedented opportunity to observe a bright comet over a wide range of heliocentric distances. We present here Spitzer Space Telescope observations of Hale-Bopp from 2005 and 2008 that show a distinct coma and tail, the presence of which is uncommon given its large heliocentric distance (21.6 AU and 27.2 AU, respectively). The morphology of the dust is compared to dynamical models to understand the activity of the comet. Our analysis shows that the shape of Hale-Bopp's dust tail in these images cannot be explained using the usual Finson-Probstein (solar gravity + solar radiation pressure) dynamical model. Several alternative explanations are explored. The analysis suggests that the most likely cause of the discrepancy is that the dust is being charged by the solar wind, then being affected by the interplanetary magnetic field via the Lorentz force. Though this effect has been explored previously, if correct, this seems to be the first time that the Lorentz force has been required to model a cometary dust tail. The analysis also suggests that Hale-Bopp was actively emitting particles when these images were taken, and the tail characteristics changed between observations. Section 1: Introduction, Background and MotivationA fundamental goal of astronomy is to understand the formation of Earth and our Solar System. Since it is impossible to observe our Solar System in its early stages, the next best thing is to study bodies that have been relatively preserved over the age of the Solar System. Comets have remained relatively unchanged since their birth as icy planetesimals in the early days of the Solar System, so they are a prime example of objects that can help us to understand the mechanics and chemistry of the planetary formation era. However, comets are not pristine; they have undergone physical and chemical alterations via various processes such as collisions (Farinella and Davis, 1996) and insolation (Huebner and Benkhoff, 1999). These changes require that we study cometary evolution to fully understand what the primordial comets were like. Section 1.1: BackgroundHale-Bopp was discovered in July of 1995, when it was inbound at a heliocentric distance of 7.2 AU. At this large distance it had already developed a coma, suggesting that activity was occurring on the nucleus at that time. It is rare to see such strong cometary activity beyond ~5 AU, so it became immediately clear that Hale-Bopp's behavior was different from that of other comets. The activity at this point was at least partially driven by the sublimation of CO (Biver et al. 1996), and transitioned to water driven activity at around 3 AU (Biver et al. 1997). When it reached its perihelion at 0.9 AU in 1997, its mass-loss rate was very high, (1.8 ± 0.4) x 10 6 kg s -1 , and the total mass loss while it was inside 3 AU was estimated to be ~ 3 x 10 13 kg (Lisse et al., 1997;Jewitt and Matthews, 1999). These extreme values were likely due to the fact that the nucleus is large (30 ± 10 km in radius and...

The Science of Sungrazers, Sunskirters, and Other Near-Sun Comets

“…Most sungrazers do not develop dust tails that can be resolved with current instrumentation, and of those that do, observations haven't yet revealed the influence of the Lorentz force on the dust (Sekanina 2000). That influence must however be significant, as the Lorentz force has to be invoked to explain some dust tails observed far from the Sun (Kramer et al 2014). Bright ordinary comets, such as C/2006 P1 McNaught, display extensive striated dust tails thought to be evidence of dust fragmentation.…”

Dynamics of HVECs emitted from comet C/2011 L4 as observed by STEREO

“…The orbital motions of supramicron particles may only be affected by extreme solar wind events, such as coronal mass ejections (CMEs) [Jones and Brandt, 2004;Jia et al, 2009]. Due to solar photon-driven photoelectric effect and solar wind sputtering, it is also expected that dust grains become charged and every low mass particle (< 0.1 μm) becomes susceptible to the effects of the HMF and the solar wind [e.g., Mendis and Horányi, 1991;Kramer et al, 2014]. C/2011 L4 (Panoramic Survey Telescope and Rapid Response System (Pan-STARRS); Figure 1), a nonperiodic comet, was discovered on 6 June 2011 at 7.9 AU heliocentric distance with an apparent magnitude of 19 [Wainscoat et al, 2011].…”

The Perihelion Emission of Comet C/2010 L5 (WISE)

“…That is, sublimation of these ices will occur beyond these heliocentric distances, just to a much lesser degree than within them (Cowan & A'Hearn 1979). We note, however, that while it is possible that cometary activity could occur at such large heliocentric distances, few comets have been observed to exhibit such behavior Szabó et al 2008Szabó et al , 2011Kramer et al 2014).…”