Finite Lifetime Fragment Model 2 for Synchronic Band Formation in Dust Tails of Comets

Nishioka, Kimihiko

doi:10.1006/icar.1998.5935

Cited by 7 publications

(6 citation statements)

References 12 publications

(4 reference statements)

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“…Since this ratio of SYORP timescales is less than 1, each successive generation of chunks will have a shorter lifetime than the previous generation, leading to a runaway cascade of fragmentation. Such a cascade is consistent with the modeling of Nishioka (1998) and Jones & Battams (2014) for the creation of dust necessary to explain striae.…”

Section: Step 4: Runaway Fragmentation Cascadesupporting

confidence: 89%

“…(3) as a relatively long--lived fragmentation cascade (Nishioka 1998, Jones & Battams 2014. Regardless of the exact details of (3), these three conditions ensure that the pre--stria materials arrive at the source location of a stria as a single unit, where the parent materials are then transformed into a daughter fragment size distribution that creates the narrow lineaments oriented towards the Sun via anti-sunward acceleration.…”

Section: Introductionmentioning

confidence: 99%

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The formation of striae within cometary dust tails by a sublimation-driven YORP-like effect

Steckloff

Jacobson

2016

Icarus

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Sublimating gas molecules scatter off of the surface of an icy body in the same manner as photons (Lambertian Scattering). This means that for every photon--driven body force, there should be a sublimation--driven analogue that affects icy bodies. Thermal photons emitted from the surfaces of asymmetrically shaped bodies in the Solar System generate net torques that change the spin rates of these bodies over time. The long--term averaging of this torque is called the YORP effect. Here we propose a sublimation--driven analogue to the YORP effect (Sublimation--YORP or SYORP), in which sublimating gas molecules emitted from the surfaces of icy bodies in the Solar System also generate net torques on the bodies. However, sublimating gas molecules carry ~10 4 --10 5 times more momentum away from the body than thermal photons, resulting in much greater body torques. Previous studies of sublimative torques focused on emissions from highly localized sources on the surfaces of Jupiter Family Comet nuclei, and have therefore required extensive empirical observations to predict the resulting behavior of the body. By contrast, SYORP applies to non--localized emissions across the entire body, which likely dominates sublimation--drive torques on small icy chunks and Dynamically Young Comets outside the Jupiter Family, and can therefore be applied without high--resolution spacecraft observations of their surfaces. Instead, we repurpose the well--tested mathematical machinery of the YORP effect to account for sublimation--driven torques. We show how an SYORP--driven mechanism best matches observations of the rarely observed, Sun--oriented linear features (striae) in the tails of comets, whose formation mechanism has remained enigmatic for decades. The SYORP effect naturally explains why striae tend to be observed between near--perihelion and ~1 AU from the Sun for comets with perihelia less than 0.6 AU, and solves longstanding problems with moving enough material into the cometary tail to form visible striae. We show that the SYORP mechanism can form striae that match the striae of Comet West, estimate the sizes of the stria--forming chunks, and produce a power--law fit to these parent chunks with a power law index of −1.4 !!.! !!.! . Lastly, we predict potential observables of this SYORP mechanism, which may appear as clouds or material that appear immediately prior to stria formation, or as a faint, wispy dust feature within the dust tail, between the nucleus and the striae.

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Section: Step 4: Runaway Fragmentation Cascadesupporting

confidence: 89%

Section: Introductionmentioning

confidence: 99%

The formation of striae within cometary dust tails by a sublimation-driven YORP-like effect

Steckloff

Jacobson

2016

Icarus

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“…Although Nishioka (1998) proposed that step (2) could be a continuous fragmentation cascade, rather than a discrete fragmentation (or dispersion) event, the general model of Sekanina and Farrell (1980) agrees well with observations of several comets (Sekanina and Farrell 1980;Sekenina and Pittichová 1997). The primary difference in later models of stria formation (Sekanina and Farrell 1980;Mendis 1980, 1981;Froehlich and Notni 1988;Kharchuk and Korsun 2010;Jones and Battams 2014;Steckloff and Jacobson 2016) is in the details of the first two steps.…”

Section: Dust Dynamics and Resultant Tail Structuressupporting

confidence: 65%

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

et al. 2017

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This review addresses our current understanding of comets that venture close to the Sun, and are hence exposed to much more extreme conditions than comets that are typically studied from Earth. The extreme solar heating and plasma environments that these objects encounter change many aspects of their behaviour, thus yielding valuable information on both the comets themselves that complements other data we have on primitive solar system bodies, as well as on the near-solar environment which they traverse. We propose clear definitions for these comets: We use the term near-Sun comets to encompass all ob- jects that pass sunward of the perihelion distance of planet Mercury (0.307 AU). Sunskirters are defined as objects that pass within 33 solar radii of the Sun's centre, equal to half of Mercury's perihelion distance, and the commonly-used phrase sungrazers to be objects that reach perihelion within 3.45 solar radii, i.e. the fluid Roche limit. Finally, comets with orbits that intersect the solar photosphere are termed sundivers. We summarize past studies of these objects, as well as the instruments and facilities used to study them, including space-based platforms that have led to a recent revolution in the quantity and quality of relevant observations. Relevant comet populations are described, including the Kreutz, Marsden, Kracht, and Meyer groups, near-Sun asteroids, and a brief discussion of their origins. The importance of light curves and the clues they provide on cometary composition are emphasized, together with what information has been gleaned about nucleus parameters, including the sizes and masses of objects and their families, and their tensile strengths. The physical processes occurring at these objects are considered in some detail, including the disruption of nuclei, sublimation, and ionisation, and we consider the mass, momentum, and energy loss of comets in the corona and those that venture to lower altitudes. The different components of comae and tails are described, including dust, neutral and ionised gases, their chemical reactions, and their contributions to the near-Sun environment. Comet-solar wind interactions are discussed, including the use of comets as probes of solar wind and coronal conditions in their vicinities. We address the relevance of work on comets near the Sun to similar objects orbiting other stars, and conclude with a discussion of future directions for the field and the planned ground-and space-based facilities that will allow us to address those science topics.

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“…Whether the submicron particles are emitted directly from the nucleus surface or are instead the product of a subsequent dust fragmentation process that occurs at the beginning of the striae (cf. the models of Sekanina and Farrell [], Pittichová et al [], and Nishioka []) is not clear—although the STEREO imagery would suggest the latter as a real possibility. Since the striae are typically only seen in very dusty comets at small heliocentric distances, we can posit the existence of a population of fractal, porous dust grains in these comets held together by materials that disrupts after a period of exposure to solar radiation and the solar wind, releasing a distribution of smaller grains that go on to form the clumps and the striae.…”

Section: Discussionmentioning

confidence: 99%

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

et al. 2015

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High-quality white-light images from the Sun-Earth Connection Coronal and Heliospheric Investigation (SECCHI) HI-1 telescope on board STEREO-B reveal high-velocity evanescent clumps (HVECs) expelled from the coma of the C/2011 L4 (Pan-STARRS) comet. The observations were recorded around the comet's perihelion (i.e., ∼0.3 AU) during the period 9-16 March 2013. Animated images provide evidence of highly dynamic ejecta moving near radially in the antisunward direction. The bulk speed of the clumps at their initial detection in the HI1-B images range from 200 to 400 km s −1 followed by an appreciable acceleration up to speeds of 450-600 km s −1 , which are typical of slow to intermediate solar wind speeds. The clump velocities do not exceed these limiting values and seem to reach a plateau. The images also show that the clumps do not expand as they propagate. The white-light images do not provide direct insight into the composition of the expelled clumps, which could potentially be composed of fine, submicron dust particles, neutral atoms and molecules, and/or ionized atomic/molecular cometary species. Although solar radiation pressure plays a role in accelerating and size sorting of small dust grains, it cannot accelerate them to velocities >200 km s −1 in the observed time interval of a few hours and distance of <10 6 km. Further, order of magnitude calculations show that ionized single atoms or molecules accelerate too quickly compared to observations, while dust grains micron sized or larger accelerate too slowly. We find that neutral Na, Li, K, or Ca atoms with > 50 could possibly fit the observations. Just as likely, we find that an interaction with the solar wind and the heliospheric magnetic field can cause the observed clump dynamical evolution, accelerating them quickly up to solar wind velocities. We thus speculate that the HVECs are composed of charged particles (dust particles) or neutral atoms accelerated by radiation pressure at > 50 values. In addition, the data suggest that clump ejecta initially move along near-radial, bright structures, which then separate into HVECs and larger dust grains that steadily bend backward relative to the comet's orbital motion due to the effects of solar radiation and gravity. These structures gradually form new striae in the dust tail. The near-periodic spacing of the striae may be indicative of outgassing activity modulation due to the comet nucleus' rotation. It is, however, unclear whether all striae are formed as a result of this process.

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Finite Lifetime Fragment Model 2 for Synchronic Band Formation in Dust Tails of Comets

Cited by 7 publications

References 12 publications

The formation of striae within cometary dust tails by a sublimation-driven YORP-like effect

The formation of striae within cometary dust tails by a sublimation-driven YORP-like effect

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

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

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