The galactic disk tidal field and the nonrandom distribution of observed Oort cloud comets

AbstractClose approaches of stars to the Solar System perturb comets from the Oort cloud so that they pass into the planetary system − the gravitational impulse changes the distribution of observable comets. This paper presents the results of calculations of the motion of stars in the solar neighbourhood in the past and future. The main results for each star are: the time of the encounter and the minimum distance between the Sun and the star. They are calculated using three different methods: a straight line motion model, a model with a Sun − star Keplerian interaction, and the numerical integration of the equations of motion with galactic perturbations included. In the last case, two models of the Galactic potential are used: a simplified potential of the Galactic disk and the more complex potential of the Galaxy by Dauphole and Colin. Coordinates and velocities of nearby stars are taken from several different catalogues: the Gliese catalogue, the Hipparcos catalogue, and the Barbier-Brossat catalogue of Radial Velocities.

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Dynamics of Comets: Recent Developments and New Challenges

Symposium - International Astronomical Union ◽

10.1017/s0074180900046568 ◽

1994 ◽

Vol 160 ◽

pp. 223-240

Author(s):

Julio A. Fernández

Keyword(s):

Solar System ◽

Inner Core ◽

Galactic Disk ◽

Kuiper Belt ◽

Oort Cloud ◽

Tidal Force ◽

Giant Molecular Clouds ◽

Recent Developments ◽

Large Telescopes ◽

Classical Picture

There is a broad consensus that long-period comets come from a huge reservoir surrounding the solar system, as proposed originally by Oort. Yet, the classical picture of the Oort cloud has substantially changed during the last decade. In addition to passing stars, the tidal force of the galactic disk and giant molecular clouds have also been identified as major perturbers of the Oort cloud. In particular, the latter may be responsible for limiting the size of the stable Oort cloud to no more than ≈ 104AU, i.e. about one tenth of the classical Oort's radius.Most comets are injected into the planetary region by the quasi-steady action of the tidal force of the galactic disk. The concentration of aphelion points of dynamically young comets toward mid-galactic latitudes is a consequence of its dominant influence. The frequency of comet passages into the inner planetary region could experience significant fluctuations with time as the Oort cloud meets random strong perturbers. The observed ordered pattern of most comet aphelia, associated with the galactic structure, argues against a recent strong perturbation of the Oort cloud.The origin of the Jupiter family has become another point of intense debate. Jupiter family comets may come from a transneptunian comet belt -the Kuiper belt- from where they can reach the planetary region through chaotic motion. The Kuiper belt has become accessible to large telescopes, as shown by the recent discoveries of 1992QB1 and 1993FW, possibly belt members. The major challenge will be to explore the region usually inaccessible to external perturbers that goes from ~30 AU to a few thousand AU. A significant mass may have been locked there from the beginnings of the solar system, giving rise to an inner core that feeds the outer or classical Oort cloud. Our aim will be to briefly discuss some of the topics summarized here.

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Mass Extinctions, Comet Impacts, and The Galaxy

Highlights of Astronomy ◽

10.1017/s1539299600020670 ◽

1998 ◽

Vol 11 (1) ◽

pp. 246-251

Author(s):

Michael R. Rampino ◽

Richard B. Stothers

Keyword(s):

Mass Extinction ◽

Galactic Plane ◽

Galactic Disk ◽

Oort Cloud ◽

Impact Craters ◽

Statistical Analyses ◽

Mass Extinctions ◽

The Galaxy ◽

Extinction Events ◽

Mass Extinction Events

Abstract The hypothesis relating mass extinctions of life on Earth to impacts of comets whose flux is partly modulated by the dynamics of the Milky Way Galaxy contains a number of postulates that can be tested by geologic evidence and statistical analyses. In an increasing number of cases, geologic evidence for impact (widespread impact debris and/or large impact craters) is found at times of mass extinction events, and the record of dated impact craters has been found to show a significant correlation with mass extinctions. Statistical analyses suggest that mass extinction events exhibit a periodic component of about 26 to 30 Myr, and periodicities of 30± 0.5 Myr and 35 ±2 Myr have been extracted from sets of well-dated impact craters. The evidence is consistent with periodic or quasi-periodic showers of impactors, probably Oort Cloud comets, with an approximately 30-Myr cycle. The best explanation for these proposed quasi-periodic comet showers involves the Sun’s vertical oscillation through the galactic disk, which may have a similar cycle time between crossings of the galactic plane.

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The Galactic Disk Tidal Force: Simulating the Observed Oort Cloud Comets

International Astronomical Union Colloquium ◽

10.1017/s0252921100046479 ◽

1997 ◽

Vol 165 ◽

pp. 149-154

Author(s):

P. A. Dybczyński ◽

H. Prȩtka

Keyword(s):

Detailed Analysis ◽

Galactic Disk ◽

Equations Of Motion ◽

Threshold Value ◽

Oort Cloud ◽

Tidal Force ◽

Statistical Characteristics ◽

Perihelion Distance ◽

Osculating Elements ◽

Averaged Hamiltonian

In previous papers (Prȩtka and Dybczyński, 1994; Dybczyński and Prȩtka, 1996) we presented detailed analysis of selected examples of the long-term evolution of the orbit of Oort cloud comets under the influence of the galactic disk tidal force, as well as some statistical characteristics of the simulated observable comet population. This paper presents further improvements in our Monte Carlo simulation programme which allow us to represent in a better way the real processes of production of observable comets due to galactic perturbations.In our second paper (Dybczyński and Prȩtka, 1996), following some other authors (see for example Matese and Whitman, 1989), we treated a comet as observable when its osculating perihelion distance decreased below some adopted observability limit (5 AU in our case). Limiting the investigation to the evolution of osculating elements allowed us to use very fast and efficient averaged Hamiltonian equations of motion in our simulation. However, further detailed analysis of the problem showed that the adopted observability definition was insufficient: what makes a comet observable is not its osculating perihelion distance but its true distance from the Sun, smaller than some adopted threshold value. It may happen that when the osculating perihelion distance is at its smallest, the comet is around its aphelion distance.

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The Galactic Disk Tidal Force: Simulating the Observed Oort Cloud Comets

Dynamics and Astrometry of Natural and Artificial Celestial Bodies ◽

10.1007/978-94-011-5534-2_17 ◽

1997 ◽

pp. 149-154 ◽

Cited By ~ 6

Author(s):

P. A. Dybczyński ◽

H. Prȩtka

Keyword(s):

Galactic Disk ◽

Oort Cloud ◽

Tidal Force

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Variability of The Oort Cloud Comet Flux: Can It be Manifest in The Cratering Record?

Highlights of Astronomy ◽

10.1017/s1539299600020682 ◽

1998 ◽

Vol 11 (1) ◽

pp. 252-256

Author(s):

J.J. Matese ◽

P.G. Whitman ◽

K.A. Innanen ◽

M.J. Valtonen

Keyword(s):

Time Series ◽

Solar System ◽

Galactic Disk ◽

Accurate Determination ◽

Oscillation Period ◽

Oort Cloud ◽

Solar Oscillation ◽

Oscillation Phase ◽

Stellar Velocity ◽

Long Time

Abstract We consider the subject of time dependence of the Oort cloud comet flux. Over long time scales the flux is likely to be dominated by the adiabatic galactic tide. This tide is substantially modulated as the Solar System moves in its galactic orbit. If Shoemaker was correct in his estimate that virtually all terrestrial craters of diameter > 100 km are produced by long period comets, then the phase and plane crossing period of the Solar System about the galactic disk should be consistent. with the ages of accurately dated large craters. A time series analysis of these ages in which the Solar oscillation phase is fixed to be consistent with observations indicates a maximal correlation for a period of 36 ± 2 Myr. This period is well within observational limits. If improvements in stellar velocity dispersion studies continue, it is possible that a sufficiently accurate determination of the Solar oscillation period can be found to unambiguously answer the following questions. Is the Solar oscillation cycle correlated with the time series of ages for large craters? If so, can we reject the hypothesis that the correlation is an artifact that could likely be reproduced by a random distribution of ages? We present evidence which suggests that if it is found that the data requires a plane crossing period in the range 36 ± 2 Myr, the answer to both of these questions will be affirmative.

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Structure in the radiation of the galactic disk

Symposium - International Astronomical Union ◽

10.1017/s0074180900101184 ◽

1967 ◽

Vol 31 ◽

pp. 355-356

Author(s):

R. D. Davies

Keyword(s):

Magnetic Field ◽

Galactic Disk ◽

Galactic Magnetic Field ◽

Measured Polarization

Observations at various frequencies between 136 and 1400 MHz indicate a considerable amount of structure in the galactic disk. This result appears consistent both with measured polarization percentages and with considerations of the strength of the galactic magnetic field.

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Dynamics of comets in the collapsing protosolar nebula

International Astronomical Union Colloquium ◽

10.1017/s0252921100031225 ◽

1999 ◽

Vol 173 ◽

pp. 45-50

Author(s):

L. Neslušan

Keyword(s):

Solar System ◽

Velocity Distribution ◽

Oort Cloud ◽

Interstellar Clouds ◽

Protosolar Nebula ◽

Moving Bodies

AbstractComets are created in the cool, dense regions of interstellar clouds. These macroscopic bodies take place in the collapse of protostar cloud as mechanically moving bodies in contrast to the gas and miscroscopic dust holding the laws of hydrodynamics. In the presented contribution, there is given an evidence concerning the Solar system comets: if the velocity distribution of comets before the collapse was similar to that in the Oort cloud at the present, then the comets remained at large cloud-centric distances. Hence, the comets in the solar Oort cloud represent a relict of the nebular stage of the Solar system.

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From the Oort cloud to Halley-type comets

International Astronomical Union Colloquium ◽

10.1017/s0252921100031638 ◽

1999 ◽

Vol 173 ◽

pp. 327-338 ◽

Cited By ~ 5

Author(s):

J.A. Fernández ◽

T. Gallardo

Keyword(s):

Total Population ◽

Complex Function ◽

Dynamical Evolution ◽

Oort Cloud ◽

Capture Process ◽

Influx Rate ◽

Short Period ◽

Dynamical Properties ◽

Orbital Periods ◽

Probability Of Capture

AbstractThe Oort cloud probably is the source of Halley-type (HT) comets and perhaps of some Jupiter-family (JF) comets. The process of capture of Oort cloud comets into HT comets by planetary perturbations and its efficiency are very important problems in comet ary dynamics. A small fraction of comets coming from the Oort cloud − of about 10−2− are found to become HT comets (orbital periods < 200 yr). The steady-state population of HT comets is a complex function of the influx rate of new comets, the probability of capture and their physical lifetimes. From the discovery rate of active HT comets, their total population can be estimated to be of a few hundreds for perihelion distancesq <2 AU. Randomly-oriented LP comets captured into short-period orbits (orbital periods < 20 yr) show dynamical properties that do not match the observed properties of JF comets, in particular the distribution of their orbital inclinations, so Oort cloud comets can be ruled out as a suitable source for most JF comets. The scope of this presentation is to review the capture process of new comets into HT and short-period orbits, including the possibility that some of them may become sungrazers during their dynamical evolution.

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How Horror Works, II

10.1093/oso/9780190666507.003.0004 ◽

2017 ◽

Author(s):

Mathias Clasen

Keyword(s):

Evolutionary History ◽

Emotional Responses ◽

Emotional Contagion ◽

Adaptive Mechanism ◽

Environmental Features ◽

Moral Disgust ◽

Nonrandom Distribution ◽

Horror Fiction

The most effective monsters of horror fiction mirror ancestral dangers to exploit evolved fears. For most of human evolutionary history, we have faced threats in the domains of predation, conspecific violence, contagion, status loss, and dangerous nonliving environmental features. We thus very easily acquire fears directed toward threats from these domains. This chapter argues that the nonrandom distribution of human fears is reflected in horror, which features stimuli that mirror evolved fears, often in incarnations that are exaggerated and/or counterintuitive for increased salience, including giant spiders, supernormal monsters such as evil clowns, and physics-violating ghosts. Many monsters are also equipped with contagion cues, thus exploiting an evolved disgust mechanism. Some monsters evoke moral disgust through their violation of norms. To strengthen audiences’ emotional responses to such monsters, horror artists often provide descriptions of characters’ reactions which are mirrored by the audience through an adaptive mechanism enabling emotional contagion.

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