Comets and nongravitational forces. V

Marsden, B. G.; Sekanina, Z.; Yeomans, Donald K.

doi:10.1086/111402

Cited by 346 publications

(354 citation statements)

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“…Non-gravitational forces were studied using the model of Marsden et al (1973). The change in 1/a was found for hypothetical comets passing through the solar system on parabolic orbits with non-gravita tional accelerations similar to those measured for some real comets.…”

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confidence: 81%

Physical and Dynamical Evolution of Long-Period Comets

Weissman

1979

Symp. - Int. Astron. Union

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Oort (1950) first suggested that the source of the long-period comets is a large spherical cloud of comets surrounding the solar system and extending roughly halfway to the nearest stars. The obser vational evidence for this is the distribution of original inverse semi-major axes of the long-period comets which shows a large spike of comets at very small positive values of l/a , less than 10"^ AIT" . Attempts to model the evolution of these comets by Oort in his original paper, by Kendall (l96l), Shteins (l96l), and Whipple (1962) were suc cessful in recreating the general shape of the l/a 0 distribution. However in each case the authors were unable to match the observed ratio of new comets from the Oort cloud versus older comets evolving under the influence of planetary perturbations.The work described here is a further study of the problem using a new method, a Monte Carlo simulation of the evolution of the long-period comets under the influence of a combination of physical and dynamical processes. Models were derived for the perturbation of cometary orbits by the major planets, by non-gravitational forces, and by random passing stars. Physical loss of comets due to planetary collision, random dis ruption (splitting), and loss of all volatiles was also modeled. These processes were combined in a computer simulation program which followed large numbers of hypothetical comets as they evolved from the Oort cloud to their eventual end-states. By changing input parameters to the com puter program it was possible to vary the relative effect of each of the different processes.In the case of planetary perturbations 5 x 10 hypothetical comets were integrated through a model solar system consisting of Jupiter and Saturn. The results were tabulated and used to derive the probability density function for the total change in l/a per perihelion passage as a function of the perihelion distance and inclination of each comet. The density function was fit with a Gaussian distribution whose standard deviation was given by a second order polynomial expansion in q and cos i. For comets with perihelia uniformly distributed between 0.01 and k AU and with random inclinations, the standard deviation was 277 R. L. Duncombe (ed.J, Dynamics of the Solar System, 277-282.

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mentioning

confidence: 81%

Physical and Dynamical Evolution of Long-Period Comets

Weissman

1979

Symp. - Int. Astron. Union

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“…This model was later on improved by Marsden et al (1973), who assumed that the sublimation of water ice acts symmetrically with respect to perihelion on a fast-rotating nucleus. The nucleus is also assumed to be spherical, and the whole surface is assumed to be isotropically outgassing.…”

Section: Introductionmentioning

confidence: 99%

“…The nucleus is also assumed to be spherical, and the whole surface is assumed to be isotropically outgassing. Marsden et al (1973) introduced the dimensionless function g(r h ), which represents the variation in the sublimation rate as a function of the heliocentric distance r h of the comet: …”

Section: Introductionmentioning

confidence: 99%

CONGO, model of cometary non-gravitational forces combining astrometric and production rate data

Maquet

Colas

Jordá

et al. 2012

A&A

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The gravitational orbit of a comet is affected by the sublimation of water molecules by the nucleus when the comet approaches perihelion. This outgassing triggers a non-gravitational force (NGF) that significantly modifies the orbit of the comet. Up to now, modelling of this effect is mostly based on an empirical model defined in the early 70s that uses a simplified outgassing model. Attempts have been made to use advanced anisotropic thermal models both to calculate the NGF taking several observational constraints into account and to retrieve the nucleus's mass and density, but (i) this approach is restricted to a handful of cometary nuclei that are sufficiently well known to allow this type of modelling, and (ii) the authors usually do not fit the astrometric measurements directly but rather non-gravitational parameters calculated with the above-mentioned empirical model. We present a new model for non-gravitational forces with the aim of revisiting the problem of NGF calculation and nucleus density determination. Our model is closer to the nucleus outgassing physics with only a few free parameters. The amplitude of the perturbation depends on several parameters describing the comet activity that can be constrained by visible, infrared, and radio observations of the coma and the nucleus of the comet. It also depends on the nucleus mass, which can in turn be determined by modelling the effect of the NGF on the orbit of a comet. The method is based on the decomposition of the surface of the nucleus in several elements located at different latitudes. The contribution of each surface element to the overall NGF is fitted from the astrometric measurements, together with the density of the nucleus. This method is the only one available so far to estimate the density of cometary nuclei from ground-based observations. This method is tested on the well-known comet 19P/Borrelly. The density found for these comet is between 150 and 600 kg m −3 .

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“…If not otherwise indicated, only Newtonian gravitational forces (including those from the eight planets) were considered. MERCURY can also calculate nongravitational (ng) forces for comets by using the symmetrical standard model by Marsden et al (1973). We integrated in time the sample of NEJFCs (each body separately) over a period of 2000 yr centred on the discovery epoch.…”

Section: The Methodsmentioning

confidence: 99%

On the asymmetric evolution of the perihelion distances of near-Earth Jupiter family comets around the discovery time

Sosa

Fernández

Pais³

2012

A&A

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We study the dynamical evolution of the near-Earth Jupiter family comets (NEJFCs) that came close to or crossed the Earth's orbit at the epoch of their discovery (perihelion distances q disc < 1.3 AU). We found a minimum in the time evolution of the mean perihelion distanceq of the NEJFCs at the discovery time of each comet (taken as t = 0) and a past-future asymmetry ofq in an interval -1000 yr, +1000 yr centred on t = 0, confirming previous results. The asymmetry indicates that there are more comets with greater q in the past than in the future. For comparison purposes, we also analysed the population of near-Earth asteroids in cometary orbits (defined as those with aphelion distances Q > 4.5 AU) and with absolute magnitudes H < 18. We found some remarkable differences in the dynamical evolution of both populations that argue against a common origin. To further analyse the dynamical evolution of NEJFCs, we integrated in time a large sample of fictitious comets, cloned from the observed NEJFCs, over a 20 000 yr time interval and started the integration before the comet's discovery time, when it had a perihelion distance q > 2 AU. By assuming that NEJFCs are mostly discovered when they decrease their perihelion distances below a certain threshold q thre = 1.05 AU for the first time during their evolution, we were able to reproduce the main features of the observedq evolution in the interval [-1000, 1000] yr with respect to the discovery time. Our best fits indicate that ∼40% of the population of NEJFCs would be composed of young, fresh comets that entered the region q < 2 AU a few hundred years before decreasing their perihelion distances below q thre , while ∼60% would be composed of older, more evolved comets, discovered after spending at least ∼3000 yr in the q < 2 AU region before their perihelion distances drop below q thre . As a byproduct, we put some constraints on the physical lifetime τ phys of NEJFCs in the q < 2 AU region. We found a lower limit of a few hundreds of revolutions and an upper limit of about 10 000-12 000 yr, or about 1600-2000 revolutions, somewhat longer than some previous estimates. These constraints are consistent with other estimates of τ phys , based either on mass loss (sublimation, outbursts, splittings) or on the extinction rate of Jupiter family comets (JFCs).

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Comets and nongravitational forces. V

Cited by 346 publications

References 0 publications

Physical and Dynamical Evolution of Long-Period Comets

Physical and Dynamical Evolution of Long-Period Comets

CONGO, model of cometary non-gravitational forces combining astrometric and production rate data

On the asymmetric evolution of the perihelion distances of near-Earth Jupiter family comets around the discovery time

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