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Title - The comet 17P/Holmes 2007 outburst: the early motion of the outburst material
By - Montalto et al, 2008
Summary - Explosive fragmentation event : On Oct 24, 2007 the periodic comet 17P / Holmes underwent an astonishing outburst that increased its apparent total brightness from magnitude 17 up to 2.5 in roughly 2 days, which is equivalent to increase in brightness by a factor of one million (Hsieh et al. 2010). The bright comet core appeared well separated from the quickly expanding dust cloud in all the data. We observed a spherically symmetric dust cloud moving away from the comet nucleus with a mean projected constant velocity of 135 m/sec, while the dust cloud was expanding with a mean constant velocity of 200 m/sec. Our estimate for the expanding coma's mass was of the order of 10^{-2}-1 comet's mass implying a significant disintegration event. We interpreted our observations in the context of an explosive scenario which was more probably originated by some internal instability processes, rather than an impact with an asteroidal body. The periodic comet 17P/Holmes was discovered in Nov 1892 (5 months past perihelion), during an outstanding brightness increase, followed by another similar event on Jan, 1893, over 2 months later. The heliocentric distance of the object at the time of the 2 major events was around 2.39 AU (1892) and 2.44 AU (2007), and the orbital inclination remained substantially unaltered during this period (i ∼ 20◦). We derived for the coma’s mass a value of 10^12 − 10^14 kg, around 10−2 − 1 comet’s mass. Generally the separation velocities of the splitting components are of the order of a few m/s, while in this case we found a projected relative velocity around 2 orders of magnitude larger. The outburst itself represents the largest apparent brightness increase ever observed for a comet.
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Title - Outburst of Comet 17P/Holmes Observed With The Solar Mass Ejection Imager
By - Jing Li et al, 2010 (includes David Jewitt)
Summary - The maximum rate of brightening occurs some 1.2 days after the onset of activity & fades over the next 5 months. At the peak the scattering, cross-section grows at 1,070 km2/s while the model-dependent mass loss rates, inferred from the lightcurve, reach a maximum at 3×10^5 kg/s. The integrated mass in the coma lies in the range (2 to 90)×10^10 kg, corresponding to 0.2% to 10% of the nucleus mass. The particulate coma mass could be contained within a shell on the nucleus of thickness ∼1.5 to 60 m. The perihelion distance is a modest 2.05 AU, small enough to drive the production of a coma through the sublimation of near-surface water ice but large enough to prevent spectacular brightness, as seen from the Earth. ("near-surface water ice" proves these scientists are very weak in temperature physics & believe in the pseudoscience of sublimation driven comet activity. Pathetic !) 17P/Holmes is distinguished by having undergone 3 dramatic photometric outbursts, the first leading to its discovery in Nov 1892, followed by an outburst in mid-Jan 1893, and the most recent on Oct 2007. In the course of a day, the comet brightened from about 17th apparent magnitude up to naked-eye visibility, with concurrent expansion of an initially circular coma at a velocity of 550 m/s, at geocentric distance 1.6 AU. More extracts.
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Title - Evolution of the Dust Trail of Comet 17P/Holmes
By - Maria Gritsevich et al, 2022
Summary - A vast amount of dust particles and gas that were ejected from the comet’s coma during the outburst spread into elliptic orbits around the Sun. This phenomenon and solar radiation pressure effect on the particles were investigated by Lyytinen et al. (2013). The evolving cloud of particles widened, apparently vanishing at first. However, Lyytinen et al (2013) re-discovered this swarm of meteoroids, which converges again at the opposite side of the Sun around the mutual (southern) node of the orbits. In one revolution the particles re-converge again at the original outburst site (referred to in this study as the near-side common node or the northern node). To the best of our knowledge, this is first direct observation of the hourglass pattern formed by the particles in the trail of a comet. Non-gravitational forces acting on the particles in a comet trail are well explained in (Vaubaillon, Colas, and Jorda, 2005). The solar radiation pressure is the result of the electromagnetic radiation emitted by the Sun exerted upon the particles. Other active forces are the Poynting and the (diurnal) Yarkovsky-Radzievskii effects produced by the anisotropy of the thermal radiation from the particles. For the first time, the hourglass pattern of a comet trail has been observed, and modeling was used to explain it. We found that spherical symmetry of the ejected particles is responsible for producing the hourglass pattern (vs. a purely theoretical case when all particles are ejected towards the sun). The spherically symmetric outburst model is not able to explain the concentration of particles implied by the sharp increase in brightness of the trail near the outburst location in Feb 2015 observations.
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By - Yoshiharu Shinnaka et al, 2018
Summary - Dust grains of crystalline silicate, which are rarely present in interstellar space, were found in cometary nuclei. These crystalline silicates are thought to have formed by annealing of amorphous silicate grains or direct condensation of gaseous materials near the Sun in the solar nebula, and incorporated into cometary nuclei in the cold comet-forming regions after radial transportation of grains in the solar nebula. Abundances of the crystalline silicate dust grains were therefore expected to be smaller farther from the Sun.
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Title - Transient Fragments in Outbursting Comet 17P/Holmes
By - Rachel Stevenson, Jan Kleyna, David Jewitt, 2010
Summary - Using image-processing techniques we probe inside the spherical dust coma and find 16 fragments having both spatial distribution and kinematics consistent with isotropic ejection from the nucleus. Photometry of the fragments is inconsistent with scattering from monolithic, inert bodies. Instead, each detected fragment appears to be an active cometesimal producing its own dust coma. By scaling from the coma of the primary nucleus of 17P/Holmes, assumed to be 1.7 km in radius (3.4 km diameter), we infer that the 16 fragments have maximum effective radii between 10 m and 100 m on UT 2007 Nov 6 (20 m & 200 m diameter). The fragments subsequently fade at a common rate of ~ 0.2 mag/day, consistent with steady depletion of ices from these bodies in the heat of the Sun. Our characterization of the fragments supports the hypothesis that a large piece of material broke away from the nucleus and crumbled, expelling smaller, icy shards into the larger dust coma around the nucleus.
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Title - A novel mechanism for outbursts of Comet 17P/Holmes and other short-period comets
By - Richard Miles, 2007
Summary - A mechanism is proposed to explain the outburst of comet 17P/Holmes based on : (a) oxidation of water within the porous surface of the comet nucleus to form hydrogen peroxide (H2O2) through exposure to UV radiation, to energetic solar-wind particles and to cosmic radiation, (b) concentration of the H2O2 component through solid-, liquid- and gas-phase processes involving sublimation, evaporation, fractional crystallization, diffusion, supercooling, capillary wetting and migration in voids within the nucleus, and (c) rapid exothermic decomposition of aqueous H2O2 liberating oxygen gas via a surface catalytic reaction through interaction with finely-dispersed transition metals, metal compounds and minerals, in particular those containing Fe, localised within a differentiated multi-component comet nucleus. An accelerated release of gaseous oxygen, concomitant self-heating and volatilisation of hydrocarbons within the nucleus results in its explosive disruption. This mechanism may also explain the observation of a repeat outburst of this comet in 1893.
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Title - Explosion of Comet 17P/Holmes as revealed by the Spitzer Space Telescope
By - William Reach et al, 2010
Summary - An explosion on comet 17P/Holmes occurred on 2007 Oct 23, projecting particulate debris of a wide range of sizes into the interplanetary medium. The orientation of the leading edge of the ejecta shell and the ejecta blob, relative to the nucleus, do not change as the orientation of the Sun changes; instead, the configuration was imprinted by the orientation of the initial explosion. The kinetic energy of the ejecta is greater than the gravitational binding energy of the nucleus. We model the explosion as being due to crystallization and release of volatiles from interior amorphous ice within a subsurface cavity; once the pressure in the cavity exceeded the surface strength, the material above the cavity was propelled from the comet. The size of the cavity and the tensile strength of the upper layer of the nucleus are constrained by the observed properties of the ejecta; tensile strengths on >10 m scale must be greater than 10 kPa. The appearance of the 2007 outburst is similar to that witnessed in 1892, but the 1892 explosion was less energetic by a factor of about 20. More extracts.
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