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Luboš Neslušan - One of the best experts on this subject based on the ideXlab platform.
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Replenishment of the comet Oort Cloud during the outward migration of Uranus and Neptune
Planetary and Space Science, 2017Co-Authors: Luboš NeslušanAbstract:Abstract In the past, the formation process of the distant comet Oort Cloud was simulated assuming the ejecting giant planets in their current orbits and with their current masses. Today, it is however known that the planets formed in a tighter configuration and the comet Cloud could be replenished, mostly, in the era of their radial migration. We simulate the Oort-Cloud formation during the planetary migration in course to see if the formation efficiency is larger than that for the stable planetary orbits. As well, we try to answer the question if the ratio of the Oort-Cloud and scattered-disk populations is larger in the case of migration in course to alleviate the problem of too a low ratio in the past simulations. The formation efficiency in the simulations with migrating planets appears to be larger than in that with the planets in stable orbits, but only for the first 100 Myr. Later, it practically disappears. The simulations with the migrating planets result in a higher ratio of the Oort-Cloud and scattered-disk populations. However, this enhancement is only moderate and cannot explain the problem of too a low ratio of both populations.
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Notes on the outer-Oort-Cloud formation efficiency in the simulation of Oort Cloud formation
Astronomy & Astrophysics, 2009Co-Authors: Piotr A. Dybczyński, Giuseppe Leto, Marian Jakubik, T. Paulech, Luboš NeslušanAbstract:Aims. The formation efficiency of the outer Oort Cloud, obtained in the simulation performed in our previous work, appeared to be very low in a comparison with the corresponding results of other authors. Performing three other simulations, we attempt to find if any of three possible reasons can account for the discrepancy. Methods. The dynamical evolution of the particles is followed by numerical integration of their orbits. We consider the perturbations by four giant planets on their current orbits and with their current masses, in addition to perturbations by the Galactic tide and passing stars. Results. The omission of stellar perturbations causes only a small increase (about ≈10%) in the population size, because the erosion by stellar perturbations prevails upon the enrichment due to the same perturbations. As a result, our different model of them cannot result in any huge erosion of the comet Cloud. The relatively shorter border, up to which we followed the dynamics of the test particles in our previous simulation, causes a significant (about a factor of ≈2) underestimate of the outer-Oort-Cloud population. Nevertheless, it by itself cannot fully account for an order-of-magnitude difference in the formation-efficiency values. It seems that the difference could mainly stem from a large stochasticity of the comet-Cloud formation process. Our maximum efficiency can grow to more than three times the corresponding minimum value when using some subsets of test particles.
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The simulation of the outer Oort Cloud formation - The first giga-year of the evolution
Astronomy & Astrophysics, 2008Co-Authors: Piotr A. Dybczyński, Giuseppe Leto, Marian Jakubik, T. Paulech, Luboš NeslušanAbstract:Aims. Considering a model of an initial disk of planetesimals that consists of 10 038 test particles, we simulate the formation of distant-comet reservoirs for the first 1 Gyr. Since only the outer part of the Oort Cloud can be formed within this period, we analyse the efficiency of the formation process and describe approximately the structure of the part formed. Methods. The dynamical evolution of the particles is followed by numerical integration of their orbits. We consider the perturbations by four giant planets on their current orbits and with their current masses, in addition to perturbations by the Galactic tide and passing stars. Results. In our simulation, the population size of the outer Oort Cloud reaches its maximum value at about 210 Myr. After a subsequent, rapid decrease, it becomes almost stable (with only a moderate decrease) from about 500 Myr. At 1 Gyr, the population size decreases to about 40% of its maximum value. The efficiency of the formation is low. Only about 0.3% of the particles studied still reside in the outer Oort Cloud after 1 Gyr. The space density of particles in the comet Cloud, beyond the heliocentric distance, r ,o f 25 000 AU is proportional to r −s ,w heres = 4.08 ± 0.34. From about 50 Myr to the end of the simulation, the orbits of the Oort Cloud comets are not distributed randomly, but high galactic inclinations of the orbital planes are strongly dominant. Among all of the outer perturbers considered, this is most likely caused by the dominant, disk component of the Galactic tide.
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A model of the current stellar perturbations on the Oort Cloud
2007Co-Authors: Giuseppe Leto, Marian Jakubik, T. Paulech, Luboš NeslušanAbstract:In a study of the Oort-Cloud dynamics, stellar perturbations should be taken into account. A model of stellar passages around the solar system has to reflect both the frequency and perihelion distribution of passing stars at the same time. We provide such a model for a 1Gyr period assuming the same Galactic environment in a solar vicinity as it is nowadays for the entire period. The modelling includes the determination of a critical distance within which all stars of a given spectral type should be considered. The resultant data com- prise the dynamical characteristics of 41589 simulated stars passing the solar system over 1Gyr. These data are available in an electronic form at http://www.astro.sk/caosp/Eedition/FullTexts/vol37no3/pp161-172.dat/. Moreover, we demonstrate that the influence of the Galactic tide on the he- liocentric trajectories of the stars, when they perturb the Oort-Cloud comets, can reliably be neglected.
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The fading problem and the population of the Oort Cloud
Astronomy & Astrophysics, 2006Co-Authors: Luboš NeslušanAbstract:Context. The discovery efficiency of the dynamically new comets has been assumed to be approximately the same as that of all long-period (LP) comets when estimating the population of the Oort Cloud. On the other hand, studies of the so-called fading problem have implied a strong difference in the discovery efficiencies of both new and old comets. Some authors have attempted to explain this discrepancy by suggesting that old comets disappeared due to the extinction or disintegration of their nuclei. Aims. We attempt to answer the question of whether the absolute brightness of old comets steeply decreases in time or whether their nuclei become extinct, dormant, or disintegrated. Moreover, we analyse the impact of the highly different discovery efficiencies on an estimate of the Oort-Cloud population. Methods. The dominance of the fading over the extinction, dormant-phase, or disintegration is demonstrated with the help of the distributions of the reciprocal semi-major axes of the original orbits of the LP comets and a more moderate decrease in discoveries of new comets with increasing perihelion distance. The comet discoveries within the LINEAR sky survey are also used to support our conclusion. Results. The demonstrated dominance of the fading implies the relatively higher discovery efficiency of new comets. Its ignorance causes an overestimation of the actual intrinsic flux of new comets through the zone of visibility compared to the corresponding intrinsic flux of all LP comets. This overestimate is also documented by a significantly smaller amount of new comets with perihelia $q \loa 3\,$AU discovered within the LINEAR. Conclusions. The actual intrinsic flux of new comets must be about one order of magnitude lower than has been derived before. Its reduction implies a one-order-of-magnitude less numerous population for the Oort Cloud. Moreover, such the reduction also solves (or, at least, weakens) the problem of too high a mass of the comet Cloud, as well as the problem of too numerous a population of predicted Halley-type objects or too high a space density of interstellar comets.
Nathan A. Kaib - One of the best experts on this subject based on the ideXlab platform.
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Oort Cloud Formation Around a Migrating Sun
2011Co-Authors: Nathan A. Kaib, Rok Roškar, Thomas QuinnAbstract:Recent numerical simulations have demonstrated that the Sun's dynamical history within the Milky Way may be much more complex than that suggested by its current low peculiar velocity. In particular, the Sun may have radially migrated through the galactic disk by up to 5-6 kpc. This has important ramifications for the structure of the Oort Cloud, as it means that the solar system may have experienced tidal and stellar perturbations that were significantly different from its current galactic environment. To characterize these effects, we use direct numerical simulations to model the formation of the Oort Cloud around migrating stars that eventually attain solar-like galactic orbits within a simulated Milky Way analog. In general, we find that our stars tend to migrate outward over time, exposing the Oort Cloud to early perturbations that were more intense than those found in the current solar neighborhood. As a result, the Oort Cloud is usually more centrally condensed due to enhanced erosion of the outer Cloud as well as enhanced trapping within the inner Cloud. Due to exposure to stronger field star impulses, approximately 25% of our Oort Cloud simulations generate Sedna-like orbits as well, suggesting that this body's orbit may be a signature of our Sun's migration within the Milky Way.
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Sedna and the Oort Cloud around a migrating Sun
Icarus, 2011Co-Authors: Nathan A. Kaib, Rok Roškar, Thomas R. QuinnAbstract:Abstract Recent numerical simulations have demonstrated that the Sun’s dynamical history within the Milky Way may be much more complex than that suggested by its current low peculiar velocity (Sellwood, J.A., Binney, J.J. [2002]. Mon. Not. R. Astron. Soc. 336, 785–796; Roskar, R., Debattista, V.P., Quinn, T.R., Stinson, G.S., Wadsley, J. [2008]. Astrophys. J. 684, L79–L82). In particular, the Sun may have radially migrated through the galactic disk by up to 5–6 kpc (Roskar, R., Debattista, V.P., Quinn, T.R., Stinson, G.S., Wadsley, J. [2008]. Astrophys. J. 684, L79–L82). This has important ramifications for the structure of the Oort Cloud, as it means that the Solar System may have experienced tidal and stellar perturbations that were significantly different from its current local galactic environment. To characterize the effects of solar migration within the Milky Way, we use direct numerical simulations to model the formation of an Oort Cloud around stars that end up on solar-type orbits in a galactic-scale simulation of a Milky Way-like disk formation. Surprisingly, our simulations indicate that Sedna’s orbit may belong to the classical Oort Cloud. Contrary to previous understanding, we show that field star encounters play a pivotal role in setting the Oort Cloud’s extreme inner edge, and due to their stochastic nature this inner edge sometimes extends to Sedna’s orbit. The Sun’s galactic migration heightens the chance of powerful stellar passages, and Sedna production occurs around ∼20–30% of the solar-like stars we study. Considering the entire Oort Cloud, we find its median distance depends on the minimum galactocentric distance attained during the Sun’s orbital history. The inner edge also shows a similar dependence but with increased scatter due to the effects of powerful stellar encounters. Both of these Oort Cloud parameters can vary by an order of magnitude and are usually overestimated by an Oort Cloud formation model that assumes a fixed galactic environment. In addition, the amount of material trapped in outer Oort Cloud orbits ( a > 20,000 AU) can be extremely low and may present difficulties for traditional models of Oort Cloud formation and long-period comet production.
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Oort Cloud formation at various Galactic distances
Astronomy and Astrophysics, 2010Co-Authors: Ramon Brasser, Arika Higuchi, Nathan A. KaibAbstract:In this study we present the results from numerical simulations of the formation of the Oort comet Cloud where we positioned the Sun in various parts of the disc of the Galaxy, starting at 2 kpc up to 20 kpc from the Galactic centre. All simulations were run for 4 Gyr. We report that the final trapping efficiency of comets in the Oort Cloud is approximately 4% and is almost independent of the solar distance from the Galactic centre. This efficiency is not enough to explain the flux of long-period comets and be consistent with the mass of the protoplanetary disc. In addition, the population ratio between the Oort Clouds and their corresponding scattered discs is at least two orders of magnitude lower than observed today. Solar migration from the inner regions of the Galaxy – where the initial trapping efficiency is higher – to farther regions – where the retention is higher – does not add enough of an effect to increase the efficiency to the necessary value of approximately 20%, so that other mechanisms for forming the Oort Cloud need to be investigated.
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2006 SQ372: A Likely Long-Period Comet from the Inner Oort Cloud
The Astrophysical Journal, 2009Co-Authors: Nathan A. Kaib, Andrew C. Becker, R. Lynne Jones, Andrew W. Puckett, Dmitry Bizyaev, Benjamin Dilday, Joshua A. Frieman, Daniel Oravetz, Kaike Pan, Thomas P. QuinnAbstract:We report the discovery of a minor planet (2006 SQ372) on an orbit with a perihelion of 24 AU and a semimajor axis of 796 AU. Dynamical simulations show that this is a transient orbit and is unstable on a timescale of ~200 Myr. Falling near the upper semimajor axis range of the scattered disk and the lower semimajor axis range of the Oort Cloud, previous membership in either class is possible. By modeling the production of similar orbits from the Oort Cloud as well as from the scattered disk, we find that the Oort Cloud produces 16 times as many objects on SQ372-like orbits as the scattered disk. Given this result, we believe this to be the most distant long-period comet (LPC) ever discovered. Furthermore, our simulation results also indicate that 2000 OO67 has had a similar dynamical history. Unaffected by the Jupiter-Saturn Barrier, these two objects are most likely LPCs from the inner Oort Cloud.
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2006 sq372 a likely long period comet from the inner Oort Cloud
arXiv: Earth and Planetary Astrophysics, 2009Co-Authors: Nathan A. Kaib, Andrew C. Becker, Andrew W. Puckett, Dmitry Bizyaev, Benjamin Dilday, Joshua A. Frieman, Lynne R Jones, Daniel OravetzAbstract:We report the discovery of a minor planet (2006 SQ372) on an orbit with a perihelion of 24 AU and a semimajor axis of 796 AU. Dynamical simulations show that this is a transient orbit and is unstable on a timescale of 200 Myrs. Falling near the upper semimajor axis range of the scattered disk and the lower semimajor axis range of the Oort Cloud, previous membership in either class is possible. By modeling the production of similar orbits from the Oort Cloud as well as from the scattered disk, we find that the Oort Cloud produces 16 times as many objects on SQ372-like orbits as the scattered disk. Given this result, we believe this to be the most distant long-period comet ever discovered. Furthermore, our simulation results also indicate that 2000 OO67 has had a similar dynamical history. Unaffected by the "Jupiter-Saturn Barrier," these two objects are most likely long-period comets from the inner Oort Cloud.
Paul R. Weissman - One of the best experts on this subject based on the ideXlab platform.
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Oort Cloud Formation and Dynamics
2004Co-Authors: Luke Dones, Paul R. Weissman, Harold F. Levison, Martin J. DuncanAbstract:The Oort Cloud is the primary source of the “nearly isotropic” comets, which include new and returning long-period comets and Halley-type comets. We focus on the following topics: (1) the orbital distribution of known comets and the cometary “fading” problem; (2) the population and mass of the Oort Cloud, including the hypothetical inner Oort Cloud; (3) the number of Oort Cloud comets that survive from the origin of the solar system to the present time, and the timescale for building the Oort Cloud; (4) the relative importance of different regions of the protoplanetary disk in populating the Oort Cloud; and (5) current constraints on the structure of the Oort Cloud and future prospects for learning more about its structure.
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The angular momentum of the Oort Cloud
Icarus, 2002Co-Authors: Paul R. WeissmanAbstract:Abstract Marochnik et al. (1988, Science 242, 547–550) estimated that the angular momentum of the Oort Cloud is between 5 × 10 52 and 2 × 10 53 g cm 2 sec −1 , two to three orders of magnitude greater than the total angular momentum of the planetary system. However, most of the angular momentum in the present-day Oort Cloud is the result of the action of external perturbers over the history of the solar system. In addition, some Oort Cloud parameters used by Marochnik et al. tend to be higher than current best estimates. It is shown that the total angular momentum of the current Oort Cloud is likely between 6.0 × 10 50 and 1.1 × 10 51 g cm 2 sec −1 , and the original angular momentum was likely a factor of 5 less than that.
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Rapid collisional evolution of comets during the formation of the Oort Cloud
Nature, 2001Co-Authors: S. Alan Stern, Paul R. WeissmanAbstract:The Oort Cloud1 of comets was formed by the ejection of icy planetesimals from the region of giant planets—Jupiter, Saturn, Uranus and Neptune—during their formation2. Dynamical simulations3,4 have previously shown that comets reach the Oort Cloud only after being perturbed into eccentric orbits that result in close encounters with the giant planets, which then eject them to distant orbits about 104 to 105 AU from the Sun (1 AU is the average Earth–Sun distance). All of the models constructed until now simulate formation of the Oort Cloud using only gravitational effects; these include the influence of the Sun, the planets and external perturbers such as passing stars and Galactic tides. Here we show that physical collisions between comets and small debris play a fundamental and hitherto unexplored role throughout most of the ejection process. For standard models of the protosolar nebula (starting with a minimum-mass nebula) we find that collisional evolution of comets is so severe that their erosional lifetimes are much shorter than the timescale for dynamical ejection. It therefore appears that collisions will prevent most comets escaping from most locations in the region of the giant planets until the disk mass there declines sufficiently that the dynamical ejection timescale is shorter than the collisional lifetime. One consequence is that the total mass of comets in the Oort Cloud may be less than currently believed.
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Stellar Encounters with the Oort Cloud Based on Hipparcos Data
The Astronomical Journal, 1999Co-Authors: Joan García-sanchez, Paul R. Weissman, Robert A. Preston, Dayton L. Jones, Jean-francois Lestrade, David W. Latham, Robert P. StefanikAbstract:We have combined Hipparcos proper-motion and parallax data for nearby stars with ground-based radial velocity measurements to —nd stars that may have passed (or will pass) close enough to the Sun to perturb the Oort Cloud. Close stellar encounters could de—ect large numbers of comets into the inner solar system, which would increase the impact hazard at Earth. We —nd that the rate of close approaches by star systems (single or multiple stars) within a distance D (in parsecs) from the Sun is given by N \ 3.5D2.12 Myr~1, less than the number predicted by a simple stellar dynamics model. However, this value is clearly a lower limit because of observational incompleteness in the Hipparcos data set. One star, Gliese 710, is estimated to have a closest approach of less than 0.4 pc 1.4 Myr in the future, and several stars come within 1 pc during a ^10 Myr interval. We have performed dynamical simulations that show that none of the passing stars perturb the Oort Cloud sufficiently to create a sub- stantial increase in the long-period comet —ux at Earths orbit.
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The Oort Cloud.
Scientific American, 1998Co-Authors: Paul R. WeissmanAbstract:Although the outermost planet, Pluto, is 6 x 10 to the 9th km from the sun, the sun's gravitational sphere of influence extends much further, out to about 2 x 10 to the 13th km. This space is occupied by the Oort Cloud, comprising 10 to the 12th-10 to the 13th cometary nuclei, formed in the primordial solar nebula. Observations and computer modeling have contributed to a detailed understanding of the structure and dynamics of the Cloud, which is thought to be the source of the long-period comets and possibly comet showers.
Hans Rickman - One of the best experts on this subject based on the ideXlab platform.
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The destruction of an Oort Cloud in a rich stellar cluster
Astronomy & Astrophysics, 2017Co-Authors: Thomas Nordlander, Hans Rickman, Bengt GustafssonAbstract:Context. It is possible that the formation of the Oort Cloud dates back to the earliest epochs of solar system history. At that time, the Sun was almost certainly a member of the stellar cluster wh ...
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The Oort Cloud and long-period comets
Meteoritics & Planetary Science, 2013Co-Authors: Hans RickmanAbstract:This review starts with a brief historical overview of the subject, after which some recent papers attempting to improve the understanding of comet injection from the Oort Cloud and the origin of new comets are discussed. Special attention is paid to the importance of nongravitational effects in comet orbit determination, the synergy between stellar encounters and the galactic tides for the injection dynamics, and the role of planetary perturbations. The field is thus shown to be advancing rapidly, and brief comments on possible implications for studying the origin of the Cloud are made.
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Planetary perturbations on Oort Cloud comets: a progress report
2011Co-Authors: Marc Fouchard, Hans Rickman, Christiane Froeschlé, Giovanni ValsecchiAbstract:We have modeled planetary perturbations on a sample of 106 Oort Cloud comets for a maximum of 1000 perihelion passages. All the four giant planets are taken into account. In order to speed up the computation of each planetary kick, the planet orbits are circular, centred onto the Sun and coplanar. The first simulations were dedicated to the definition of the heliocentric distance rs from which the numerical integration required for the computation of each kick should start, and also below which perihelion distance qs a planetary kick should be computed. It appears that rs=100 au, and qs=37 au are suitable values for our goal. Then the transparency factor of our Solar System was investigated. It appears that it is above 80% only for perihelion distance q smaller than 5 au.For q > 10 au, it drops to value smaller than 10%. Our solar system seems to be more transparent that it is usually thought. Then we have studied the evolution of a sample of 1 Million of comets with perihelion in the planetary region of the Solar system affected by the planetary perturbations only. It appears that for q10 au, many comets support more than 1000 planetary kicks without being ejected from the Oort Cloud.
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Long‐term evolution of Oort Cloud comets: capture of comets
Monthly Notices of the Royal Astronomical Society, 2002Co-Authors: Pasi Nurmi, Mauri Valtonen, J. Q. Zheng, Hans RickmanAbstract:ABSTRA C T We test different possibilities for the origin of short-period comets captured from the Oort Cloud. We use an efficient Monte Carlo simulation method that takes into account nongravitational forces, Galactic perturbations, observational selection effects, physical evolution and tidal splittings of comets. We confirm previous results and conclude that the Jupiter family comets cannot originate in the spherically distributed Oort Cloud, since there is no physically possible model of how these comets can be captured from the Oort Cloud flux and produce the observed inclination and Tisserand constant distributions. The extended model of the Oort Cloud predicted by the planetesimal theory consisting of a non-randomly distributed inner core and a classical Oort Cloud also cannot explain the observed distributions of Jupiter family comets. The number of comets captured from the outer region of the Solar system are too high compared with the observations if the inclination distribution of Jupiter family comets is matched with the observed distribution. It is very likely that the Halley-type comets are captured mainly from the classical Oort Cloud, since the distributions in inclination and Tisserand value can be fitted to the observed distributions with very high confidence. Also the expected number of comets is in agreement with the observations when physical evolution of the comets is included. However, the solution is not unique, and other more complicated models can also explain the observed properties of Halley-type comets. The existence of Jupiter family comets can be explained only if they are captured from the extended disc of comets with semimajor axes of the comets a , 5000 au. The original flattened distribution of comets is conserved as the cometary orbits evolve from the outer Solar system era to the observed region.
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Orbits of Short Period Comets Captured from the Oort Cloud
Earth Moon and Planets, 1996Co-Authors: J. Q. Zheng, Mauri Valtonen, Seppo Mikkola, M. Korpi, Hans RickmanAbstract:Oort Cloud comets occasionally obtain orbits which take them through the planetary region. The perturbations by the planets are likely to change the orbit of the comet. We model this process by using a Monte Carlo method and cross sections for orbital changes, i.e. changes in energy, inclination and perihelion distance, in a single planet-comet encounter. The influence of all major planets is considered. We study the distributions of orbital parameters of observable comets, i.e. those which have perihelion distance smaller than a given value. We find that enough comets are captured from the Oort Cloud in order to explain the present populations of short period comets. The median value of cos i for the Jupiter family is 0.985 while it is 0.27 for the Halley types. The results may explain the orbital features of short period comets, assuming that the active lifetime of a comet is not much greater than 400 orbital revolutions.
Piotr A. Dybczyński - One of the best experts on this subject based on the ideXlab platform.
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Notes on the outer-Oort-Cloud formation efficiency in the simulation of Oort Cloud formation
Astronomy & Astrophysics, 2009Co-Authors: Piotr A. Dybczyński, Giuseppe Leto, Marian Jakubik, T. Paulech, Luboš NeslušanAbstract:Aims. The formation efficiency of the outer Oort Cloud, obtained in the simulation performed in our previous work, appeared to be very low in a comparison with the corresponding results of other authors. Performing three other simulations, we attempt to find if any of three possible reasons can account for the discrepancy. Methods. The dynamical evolution of the particles is followed by numerical integration of their orbits. We consider the perturbations by four giant planets on their current orbits and with their current masses, in addition to perturbations by the Galactic tide and passing stars. Results. The omission of stellar perturbations causes only a small increase (about ≈10%) in the population size, because the erosion by stellar perturbations prevails upon the enrichment due to the same perturbations. As a result, our different model of them cannot result in any huge erosion of the comet Cloud. The relatively shorter border, up to which we followed the dynamics of the test particles in our previous simulation, causes a significant (about a factor of ≈2) underestimate of the outer-Oort-Cloud population. Nevertheless, it by itself cannot fully account for an order-of-magnitude difference in the formation-efficiency values. It seems that the difference could mainly stem from a large stochasticity of the comet-Cloud formation process. Our maximum efficiency can grow to more than three times the corresponding minimum value when using some subsets of test particles.
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The simulation of the outer Oort Cloud formation - The first giga-year of the evolution
Astronomy & Astrophysics, 2008Co-Authors: Piotr A. Dybczyński, Giuseppe Leto, Marian Jakubik, T. Paulech, Luboš NeslušanAbstract:Aims. Considering a model of an initial disk of planetesimals that consists of 10 038 test particles, we simulate the formation of distant-comet reservoirs for the first 1 Gyr. Since only the outer part of the Oort Cloud can be formed within this period, we analyse the efficiency of the formation process and describe approximately the structure of the part formed. Methods. The dynamical evolution of the particles is followed by numerical integration of their orbits. We consider the perturbations by four giant planets on their current orbits and with their current masses, in addition to perturbations by the Galactic tide and passing stars. Results. In our simulation, the population size of the outer Oort Cloud reaches its maximum value at about 210 Myr. After a subsequent, rapid decrease, it becomes almost stable (with only a moderate decrease) from about 500 Myr. At 1 Gyr, the population size decreases to about 40% of its maximum value. The efficiency of the formation is low. Only about 0.3% of the particles studied still reside in the outer Oort Cloud after 1 Gyr. The space density of particles in the comet Cloud, beyond the heliocentric distance, r ,o f 25 000 AU is proportional to r −s ,w heres = 4.08 ± 0.34. From about 50 Myr to the end of the simulation, the orbits of the Oort Cloud comets are not distributed randomly, but high galactic inclinations of the orbital planes are strongly dominant. Among all of the outer perturbers considered, this is most likely caused by the dominant, disk component of the Galactic tide.
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Simulating observable comets. III. Real stellar perturbers of the Oort Cloud and their output
Astronomy & Astrophysics, 2006Co-Authors: Piotr A. DybczyńskiAbstract:Context. This is the third of a series of papers on simulating the mechanisms acting currently on the Oort Cloud and producing the observed long-period comets. Aims. In this paper we investigate the influence of current stellar perturbers on the Oort Cloud of comets under the simultaneous galactic disk tide. We also analyse the past motion of the observed long-period comets under the same dynamical model to verify the widely used definition of dynamically new comets. Methods. The action of nearby stars and the galactic disk tide on the Oort Cloud was simulated. The original orbital elements of all 386 long-period comets of quality classes 1 and 2 were calculated, and their motion was followed numerically for one orbital revolution into the past, down to the previous perihelion. We also simulated the output of the close future pass of GJ 710 through the Oort Cloud. Results. The simulated flux of the observable comets resulting from the current stellar and galactic perturbations, as well as the distribution of perihelion direction, was obtained. The same data are presented for the future passage of GJ 710. A detailed description is given of the past evolution of aphelion and perihelion distances of the observed long-period comets. Conclusions. We obtained no fingerprints of the stellar perturbations in the simulated flux and its directional structure. The mechanisms producing observable comets are highly dominated by galactic disk tide because all current stellar perturbers are too weak. Also the effect of the close passage of the star GJ 710 is very difficult to recognise on the background of the Galactic-driven observable comets. For the observed comets we found only 45 to be really dynamically “new” according to our definition based on the previous perihelion distance value.
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The statistical effects of galactic tides on the Oort Cloud
Earth Moon and Planets, 1996Co-Authors: Piotr A. Dybczyński, H. PretkaAbstract:This report is a comment on two papers by Matese and Whitman (1989, 1992). We discuss here the applicability of uniform probability densities for the orbital parameters of the Oort Cloud comets.
