Cometary Outbursts Research Articles

THE OUTBURST OF COMET 17P/HOLMES

Comet 17P/Holmes had a massive outburst at approximately 2007 October 23.8 and its total brightness reached maximum (from m = 17 to m = 2.5) around 2007 October 25, about 1.7 days (42 hr) after the event. Following the first report of this extraordinary cometary outburst, comprehensive observations were obtained at the Lulin Observatory until early 2008 January by using broadband filters and narrowband cometary filters. The separation velocity, as projected on the plane of the sky, between the nucleus and the coma blob produced by the outburst has been estimated to be 0.132 ± 0.004 km s −1 from October 25.8 to November 1.6. The expansion speed, also projected on the plane of the sky of the dust shell has been found to be constant at a rate of approximately 0.554 ± 0.005 km s −1 from October 25.8 to November 1.6. The color on December 10 is slightly redder than that of the Sun. Our narrowband observations provide information on the production rates of gas species on October 31: log Q (CN) = 27.103 and log Q (C2) = 27.349. The resulting abundance ratios show that the 17P can be classified as a typical comet in terms of composition.

Large cometary grains - their destruction and changes in the luminosity of comets

The catastrophic thermodynamic destruction of large cometary heterogeneous grains lying on the surface of a comet nucleus is examined. The core–mantle grain-structure model is assumed. Grain fragmentation as an explanation of sudden changes in cometary brightness is proposed. The approach presented to the problem of cometary outbursts is a development of a previous author's paper. The proposed mechanism is based on the idea of thermodynamical destruction of heterogeneous cometary grains. Numerical simulations have been carried out for a wide range of values of physical characteristics of cometary material. The results obtained are consistent with observational data. The main conclusion of this paper is that thermodynamical fragmentation of large grains can explain variations in brightness and also outbursts of comets.

Optical properties of dust from Jupiter family comets

To try to define specific physical properties of the dust of Jupiter-family comets (JFCs), we compare the light scattered by them. Amongst the more than 1000 JFCs, less than 200 are numbered, 40 of them being rather bright. In the present work we use data from the latter. In situ observations of three nuclei show low albedo surfaces. The albedo of the dust particles in the coma is low, with generally a red colour. The A( α) fρ product is a measure of cometary activity and secular changes. Images of different regions (jets and fans) give indications on the nucleus rotation and position of the emitting areas, as compared to the position of the rotation axis. Differences in physical properties between the particles in different regions are pointed out by differences in the linear polarization of the scattered light and by spectral variations in brightness and polarization. Jupiter family comets are considered as dust-poor comets. Tails and trails’ studies give an estimation of the size distribution of the particles. However the dust production rates depend on the largest particles (up to centimetre size), which are mainly observed in the trails where large dark compact particles are found. These dark particles are also responsible for the high polarization in the inner most coma of some comets. The meaning, in terms of physical properties, of the linear polarization is discussed through different examples such as 2P/Encke, 9P/Tempel 1 or the fragments of 73P/Schwassmann-Wachmann 3. Cometary outbursts and splitting events show that the properties of the dust ejected from the interior of the nucleus are similar to the ones of more active comets (new or with larger semi-major axis).

A mechanism for short-lived cometary outbursts at sunrise as observed by Deep Impact on 9P/Tempel 1

Abstract We explore a possible mechanism that may explain the outbursts observed by the Deep Impact mission on comet 9P/Tempel 1 that appear to occur near sunrise on a particular area. Assuming that the area is covered by a porous, poorly conducting dust layer, the heat wave generated by solar radiation at local noon propagates through the dust layer towards the ice-rich layer underneath it. The heated ice sublimates and the vapour flows towards the surface. However, by the time the heat wave reaches the ice, the spot has moved out of sunlight and its temperature has started dropping. As the vapour flows outwards, the surface has become so cold that it refreezes. Thus, at night some ice accumulates in the dust layer, very close to the surface. At sunrise, it immediately evaporates, producing a short-lived surge of activity. Numerical simulations of this mechanism provide the duration and water production of such outbursts, which are compatible with the 9P/Tempel 1 observations of small outbursts.

A Model of the Early Evolution of the 2007 Outburst of Comet 17P/Holmes

We have conducted a morphological analysis of the dust features generated during the first 5 weeks after the 2007 October outburst of comet 17P/Holmes. We used a computer simulation technique to generate synthetic images of dust ejecta released from discrete sources on a rotating nucleus. We found that the main jets are caused by discrete sources located near the south pole of the nucleus, while particle ejection is otherwise produced on the whole sunlit southern hemisphere, causing the observed dust shell in the sunward direction. The rotational parameters we derived (Φ = 213° and I = 90°, or the north pole pointing to R.A. = 38.8°, decl. = +35.1°) indicate that the subsolar latitude was near –90° at the outburst time. Assuming the same dust distribution function everywhere on the comet surface, and the same particle size dependence on the velocity, the ejection velocities for particles forming the jets must be remarkably different, by a factor of ~5 slower, than the background hemispherical particle emission. Based on a comparison of synthetic images with cometary images obtained during the 1892 outburst, we show that the rotational parameters are remarkably consistent during both 1892 and 2007 apparitions.

Elementary? Comet outburst caught by the INT

Elementary? Comet outburst caught by the INT

Cometary outbursts - the post-Deep Impact outlook on collisions as possible causes

The possibility of impacts between comets belonging to the Jupiter Family and other small bodies orbiting in the main asteroid belt, and the consequences in relation to cometary activity are discussed. The probability of such events and the jumps in cometary brightness caused by impacts are examined. The results are compared with the results of the Deep Impact mission to Comet 9P/Tempel 1. The main conclusion of this paper is in agreement with previous findings, namely that an impact mechanism cannot be the main cause of the outburst activity of comets.

A model of cometary outbursts based on the idea of fragmentation of ice grains

Abstract In this Letter the mechanism of destruction of ice grains as the cause of cometary outbursts and variations of brightness is reviewed. Such destruction can arise from the combination of two causes: inclusions of chemical compounds that are much more volatile than water-ice placed inside cometary water-ice grains; and the influence of the solar wind on such heterogeneous grains. Numerical calculations have been carried out for a large range of values of probable physical characteristics of cometary material. This approach gives a simulated increase in the cometary brightness that is consistent with the observed one. It is concluded that this mechanism is a probable and real explanation of the sudden activity of comets at a wide range of heliocentric distances.

The search for a cometary outbursts mechanism: a comparison of various theories

AbstractIn the paper the potential sources of energy of cometary outbursts have been reviewed. Considerations focus on four probable sources of the outbursts' energy. These are the polymerization of hydrogen cyanide HCN, impacts with the meteoroids, destruction of cometary grains in the field of strong solar wind and the transformation of amorphous water Ice into the crystalline one. The values of released energy and jumps of cometary brightness caused by these mechanisms have been discussed. A modern approach to the problem of the thermodynamical evolution of the comet nucleus which includes amorphous water ice is considered as the starting point in the discussion presented in the paper. The main characteristics of an outburst of a hypothetical comet belonging to the Jupiter family comet are calculated. The obtained results are in a good agreement with the characteristics observed during the real outbursts of comets. The main conclusion of this paper confirms a general presumption that the cometary outbursts can have different causes. However, the hypothesis concerning the amorphous water ice transformation appears to be the most probable one. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Hypervelocity experiments of impact cratering and catastrophic disruption of targets representative of minor bodies of the Solar System

Impact processes influence the surface evolution of the solid bodies in the Solar System, as asteroids or comets. The better understanding of these phenomena can improve the interpretation of remote sensing data from forthcoming missions. In order to complement and to extend the available data on hypervelocity impacts on porous targets to ranges of velocity and physical conditions not yet explored, we focused our work on catastrophic fragmentation and cratering processes onto porous targets by means of high velocity impact experiments using a two-stage light-gas gun located at the impact facility of CISAS “G. Colombo” of the University of Padova. Tests have been performed on targets of different materials, e.g. glass ceramic foam, natural pumices, water ice, and different porosity (with density in the range from 0.35 to 1.07 g/cm 3 and porosity from 2% up to 65%). Results have been analysed and compared to published data. In particular, cratering morphology is studied as function of projectile velocity and density and then it is compared to empirical trend reported in Kadono [Kadono, T. Hypervelocity impact into low density material and cometary outburst. Planet. Space Sci., 47, 305–318, 1999.] with good agreement. Our tests results revealed that porosity seems to induce a rapid attenuation of the shock affecting energy propagation inside the target; craters generated by hypervelocity impacts on porous targets are smaller and much deeper than those of non porous targets. Fragments distribution resulting from disruption tests is analysed and the largest fragment mass has been studied as function of the collisional specific energy; results is compared to those of paper by Ryan et al. [Ryan, E.V., Davis, D.R., Giblin, I. A laboratory impact study of simulated edgeworth-Kuiper belt objects. Icarus 142, 56–62, 1999.]. Furthermore, numerical simulations have been performed by using Smooth Particle Hydrodynamics (SPH) and Lagrangian grid technique in order to test some available numerical models for a forthcoming more accurate numerical analysis that will be validated with the comparison with experimental results.

Xenomict energy in cold solids in space

Minerals on earth whose crystalline order has been reduced by radioactive decay of contained atoms are termed "metamict." They are rare and few because in most crystalline solids, atoms and vacancies are relatively mobile at terrestrial temperatures, and radiation damage tends to be self-annealing. This is not the case in the extreme cold of deep space. Below roughly 100 K, reduced vacancy mobility allows cosmic ray and solar wind induced lattice defects to endure and accumulate for eons, reaching energy densities of up to MJ kg(-1) in some materials. We examine the possible effects of the release of energy stored in cold deep-space materials when solid-state defects recombine upon warming due to impacts, gravitational infall, or perihelion. Dimensional analysis suggests energetic defect recombination in radiation-damaged "xenomict" solids in comets, and planetesimals may, in some circumstances, raise internal temperatures enough to melt ice and volatilize frozen gases. We speculate that this may account for some cometary outbursts and Deep Impact experiment results. Calorimetric experiments on appropriately irradiated natural and synthetic materials are needed to further quantify these mechanisms.

New peculiarities of cometary outburst activity

The results of investigations of visual light curves, brightness outburst activity and photometrical evolution of some comets are presented. The peculiarities of brightness outbursts distribution on heliocentric distance, of temporal variations of outburst activity, outbursts correlation with sudden changes of power law coefficient and outbursts relation with precision positions of comets are discussed. The new phenomena found by authors must be taken into account when a mechanism of the cometary outburst activity is developed.

A large dust/ice ratio in the nucleus of comet 9P/Tempel 1

Comets spend most of their life in a low-temperature environment far from the Sun. They are therefore relatively unprocessed and maintain information about the formation conditions of the planetary system, but the structure and composition of their nuclei are poorly understood. Although in situ and remote measurements have derived the global properties of some cometary nuclei, little is known about their interiors. The Deep Impact mission shot a projectile into comet 9P/Tempel 1 in order to investigate its interior. Here we report the water vapour content (1.5 10(32) water molecules or 4.5 10(6) kg) and the cross-section of the dust (330 km2 assuming an albedo of 0.1) created by the impact. The corresponding dust/ice mass ratio is probably larger than one, suggesting that comets are 'icy dirtballs' rather than 'dirty snowballs' as commonly believed. High dust velocities (between 110 m s(-1) and 300 m s(-1)) imply acceleration in the comet's coma, probably by water molecules sublimated by solar radiation. We did not find evidence of enhanced activity of 9P/Tempel 1 in the days after the impact, suggesting that in general impacts of meteoroids are not the cause of cometary outbursts.

The source of energy of the comet 29P/Schwassmann-Wachmann 1 outburst activity: the test of the summary

The comet 29P/Schwassmann-Wachmann 1 is an exceptional comet as far as cometary outbursts are concerned. Despite its large distance from the Sun (about 6 au), it shows quasi-regular outburst activity, usually once or twice a year. Up to now there has not been a generally accepted model that explains this phenomenon. In the first part of this paper, the most well-known hypotheses that attempt to explain the outburst activity of this comet are presented and critically analysed. The main aim of this paper is to present a model for the outburst activity of this comet. The model is based on the global analysis of the internal structure and physical and chemical processes that take place in the cometary nucleus. Numerical calculations were carried out for reasonable assumed values of a large range of cometary characteristics. The obtained results are consistent with observational data.

05/00685 Co-provision in sustainable energy systems: the case of micro-generation

We propose a mechanism based on the rubble-pile hypothesis of the cometary nucleus (Weissman 1986, Nature320, 242–244) to explain the catastrophic breakup of comet LINEAR (C/1999 S4) observed during July–August 2000. We suggest that a solid nucleus made up of 10–100 m “cometesimals” (Weidenschilling 1997, Icarus127, 290–306) contains a network of interconnected voids in the intercometesimal regions. The production of super-volatile (i.e., species more volatile than water) gasses into these voids occurs as a result of the thermal wave propagating through the nucleus and associated phase transitions of water ice. The network of voids provides an efficient pathway for rapid propagation of these gasses within the nucleus resulting in gas pressure caused stresses over a wide regime of the nucleus. This provides a mechanism for catastrophic breakups of small cometary nuclei such as comet LINEAR (C/1999 S4) as well as for some observed cometary outbursts including those that occur at large heliocentric distances (e.g., West et al. 1991, Astron. Astrophys.246, L77–L80). We emphasize the importance of techniques such as radar reflection tomography and radiowave transmission tomography (e.g., Kofman et al. 1998, Adv. Space Res. 21, 1589–1598) aboard cometary missions to determine the three-dimensional structure of the nucleus, in particular the extent of large-scale voids.

Cometary outbursts: re-discussion of collision causes - the application to the comet 29P/Schwassmann-Wachmann 1

In this paper, a source of cometary outbursts is examined. As a potential cause of some outbursts, impacts of a comet with meteoroids are considered. The probabilities and consequences of such events have been investigated in relation to the case of the Comet 29P/Schwassmann–Wachmann 1 outbursts. This paper focuses on two problems. The first one concerns the changes in brightness of the comet after the impact of a meteoroid into its nucleus. It is shown that impacts of comets with even metre‐sized solid impactors give an immediate considerable jump in their brightness consistent with that observed during real outbursts. The second problem is to estimate how real such events are. It is concluded that the probability of impacts with metre‐sized projectiles in relation to the Comet 29P/Schwassmann–Wachmann 1 is very low – practically negligible. The possibility of self‐bombardment of this comet by pieces of cometary material ejected earlier from its nucleus was also discussed. It is shown that the probability of such events is also hardly probable. That is why the main conclusion of this paper is that the impact mechanism could not trigger the outburst activity of the considered comet.

Are the cometary outbursts caused by impacts with interplanetary vagabonds probable?

AbstractThe possibility of impacts and their results in relation to the cometary outbursts between comets and other small bodies in the solar system has been investigated. Taking into consideration certain physical features of cometary nuclei and impacting bodies, the probability of impacts of small bodies moving in the main asteroid belt with hypothetical comets which represent three types: Jupiter family comets, Halley family comets and long period comets has been computed. The probability of impacts between comets and meteoroids at large heliocentric distances has also been estimated. Potential consequences of these events in relation to outbursts of the cometary brightness have been discussed. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

SOHO/LASCO observation of an outburst of Comet 2P/Encke at its 2000 perihelion passage

Comet 2P/Encke was observed with the SOHO/LASCO C2 and C3 coronagraphs over a time interval of 11 days, starting 4 days before its September 2000 perihelion passage and through several broadband visible filters. The lightcurve reveals an outburst which started 4.9 days after perihelion, with the brightness of the coma increasing by 1.5 mag in just a few hours and progressively decreasing thereafter, probably going back to its original state in about 9 days. The color information indicates that an approximately solar color continuum was detected, implying that the observed signals were dominated by solar light scattered off submillimetric dust grains. We propose that the rapid migration of the subsolar point over the southern hemisphere during the perihelion passage activates one or several new active regions enriched in submillimetric grains, with the observed outburst corresponding to the initial blow-off of their mantle. This scenario is consistent with other observations and implies that the south polar region of the nucleus of 2P/Encke has very distinct properties.

Peculiarities of Cometary Light Curves and Outburst Activity

We give an overview of the main results of our works on the revision of cometary light curves and on the search for new patterns and features in the evolution of the integrated brightness of comets as they move in circumsolar space. These works revealed several new, previously unknown phenomena in the integrated-brightness variations and outburst activity of comets. Our results supplement and expand the body of observational data that provides a basis for constructing a model of the cometary nucleus and developing a theory of the cometary evolution.

Outbursts of comets—the case of 1P/Halley

Possible mechanisms that were the reason of the unexpected strong outburst of 1P/Halley observed on February 12, 1991 at 14.3 AU heliocentric distance have been considered. As a plausible mechanism, a combination of the polymerization of HCN with the amorphous water–ice transformation has been proposed. Probably, the electrostatic destruction of cometary grains in the cometary coma also took place. Calculations have been carried out for a large range of cometary parameters and it has been shown that the proposed scenario of the outburst gives a jump in the comet brightness which is consistent with the real jump observed during the 1P/Halley outburst.