Past Orbits Research Articles

한국의 고대 혜성 기록 분석

We have analyzed the comet records in the Korean history books: Samguksagi, Goryeosa, and Joseonwangjosillok. For a comparison, the Chinese and Japanese comet records collected by Kronk (1999) have also been analyzed. Power spectrum of the time series of the comet records is used to find periodic comets. Statistically significant periodicities in the power spectrum are detected at the periods of 38-40 years, about 76 years, and 300-400 years for all Korean, Chinese, and Japanese comet records. We have also calculated the past orbits of some comets that have been recently observed, to check whether or not they were recorded in the history books. We use a multistep method to numerically integrate the comet`s orbital motion backward in time to 51 B.C. The gravitational force due to the Sun and the nine planets, non-gravitational force, and the relativistic effects have been considered. Comparison of comet`s perihelion passage time and the position on the sky with the historical records shows that the comet Halley were recorded at every passage in both Goryeo and Joseon periods. The orbital motion of the comet Pons-Brooks has also been compared with the Korean records. For the comet Tempel-Tuttle, Swift-Tuttle, and Ikeya-Zhang, we have compared our calculation of the orbital motions with those of the previous studies.

Evidence for a Past High-Eccentricity Lunar Orbit

The large differences between the Moon's three principal moments of inertia have been a mystery since Laplace considered them in 1799. Here we present calculations that show how past high-eccentricity orbits can account for the moment differences, represented by the low-order lunar gravity field and libration parameters. One of our solutions is that the Moon may have once been in a 3:2 resonance of orbit period to spin period, similar to Mercury's present state. The possibility of past high-eccentricity orbits suggests a rich dynamical history and may influence our understanding of the early thermal evolution of the Moon.

Dynamical Evolution of the TW Hydrae Association

Using Galactic dynamics we have determined the age of the low-mass post-T Tauri stars in the TW Hya Association (TWA). To do so we applied the method of Ortega and coworkers to five stars of the association with Hipparcos-measured distances (TWA 1, TWA 4, TWA 9, TWA 11, and TWA 19). The method is based on the calculation of the past three-dimensional orbits of the stars. Of these stars, only TWA 9 presents a quite different orbit so that it does not appear to be a dynamical member of the TWA. The four remaining stars have their first maximum orbital confinement at the age of -8.3 ± 0.8 Myr, which is considered the dynamical age of the TWA. This confinement fixes the probable three-dimensional forming region of the TWA within a mean radius of 14.5 pc. This region is related to the older subgroups of the Sco-Cen OB association, Lower Centaurus Crux and Upper Centaurus Lupus, both with a mean age of about 18 Myr. This dynamical age of the TWA and that of the β Pic Moving Group, 11 Myr, also discussed here, introduce a more precise temporal scale for studies of disk evolution and planetary formation around some stars of these associations. Using the retraced orbit of the runaway star HIP 82868 we examine the possibility that the formation of the TWA was triggered by a supernova explosion. It is shown that for the four considered TWA stars, the expansion in volume is a factor of 5 from their origin to the present state. This is mainly due to the currently more distant star TWA 19.

The spin state of 433 Eros and its possible implications

In this paper, we show that Asteroid (433) Eros is currently residing in a spin–orbit resonance, with its spin axis undergoing a small-amplitude libration about the Cassini state 2 of the proper mode in the nonsingular orbital element sin I / 2 exp ( ı Ω ) , where I the orbital inclination and Ω the longitude of the node. The period of this libration is ≃53.4 kyr. By excluding these libration wiggles, we find that Eros' pole precesses with the proper orbital plane in inertial space with a period of ≃61.4 kyr. Eros' resonant state forces its obliquity to oscillate with a period of ≃53.4 kyr between ≃76° and ≃89.5°. The observed value of ≃89° places it near the latter extreme of this cycle. We have used these results to probe Eros' past orbit and spin evolution. Our computations suggest that Eros is unlikely to have achieved its current spin state by solar and planetary gravitational perturbations alone. We hypothesize that some dissipative process such as thermal torques (e.g., the so-called YORP effect) may be needed in our model to obtain a more satisfactory match with data. A detailed study of this problem is left for future work.

Assessing NEO hazard mitigation in terms of astrodynamics and propulsion systems requirements.

Uncertainties associated with assessing valid near-Earth object (NEO) threats and carrying out interception missions place unique and stringent burdens on designing mission architecture, astrodynamics, and spacecraft propulsion systems. A prime uncertainty is associated with the meaning of NEO orbit predictability regarding Earth impact. Analyses of past NEO orbits and impact probabilities indicate uncertainties in determining if a projected NEO threat will actually materialize within a given time frame. Other uncertainties regard estimated mass, composition, and structural integrity of the NEO body. At issue is if one can reliably estimate a NEO threat and its magnitude. Parameters that determine NEO deflection requirements within various time frames, including the terminal orbital pass before impact, and necessary energy payloads, are quantitatively discussed. Propulsion system requirements for extending space capabilities to rapidly interact with NEOs at ranges of up to about 1 AU (astronomical unit) from Earth are outlined. Such missions, without gravitational boosts, are deemed critical for a practical and effective response to mitigation. If an impact threat is confirmed on an immediate orbital pass, the option for interactive reconnaissance, and interception, and subsequent NEO orbit deflection must be promptly carried out. There also must be an option to abort the mitigation mission if the NEO is subsequently found not to be Earth threatening. These options require optimal decision latitude and operational possibilities for NEO threat removal while minimizing alarm. Acting too far in advance of the projected impact could induce perturbations that ultimately exacerbate the threat. Given the dilemmas, uncertainties, and limited options associated with timely NEO mitigation within a decision making framework, currently available propulsion technologies that appear most viable to carry out a NEO interception/mitigation mission within the greatest margin of control and reliability are those based on a combined (bimodal) nuclear thermal/nuclear electric propulsion platform. Elements of required and currently available performance characteristics for nuclear and electric propulsion systems are also discussed.

On the Kinematics of Tidal Debris from Omega Cen's Progenitor Galaxy

AbstractThe kinematic properties of tidal debris from an orbiting Galactic satellite is presented, on the assumption that its central part once contained the most massive Galactic globular cluster, ω Cen. We simulate dynamical evolution of a satellite galaxy that follows the present-day and likely past orbits of ω Cen, and analyse the kinematic nature of their tidal debris and randomly generated Galactic stars comprising spheroidal halo and flat disk components. It is found that the debris stars show a retrograde rotation at ∼–100 km s–1, which may accord with a recently discovered stellar stream at a radial velocity of ∼300 km s–1 towards the Galactic longitude of ∼270°. These stars also contribute, only in part, to a reported retrograde motion of the outer halo in the north Galactic pole direction, without significantly modifying local halo kinematics near the Sun. The prospects for future debris searches and the implications for the early evolution of the Galaxy are briefly presented.

Kinematics of Tidal Debris from Centauri's Progenitor Galaxy

We present the kinematic properties of a tidally disrupted dwarf galaxy in the Milky Way, based on the hypothesis that its central part once contained the most massive Galactic globular cluster, ω Cen. Dynamical evolution of a self-gravitating progenitor galaxy that follows the present-day and likely past orbits of ω Cen is calculated numerically and the kinematic nature of their tidal debris is analyzed, combined with randomly generated stars comprising spheroidal halo and flat disk components. We show that the retrograde rotation of the debris stars at ~-100 km s-1 accords with a recently discovered large radial velocity stream at ~300 km s-1 toward the Galactic longitude of ~270°. These stars also contribute, only in part, to a reported retrograde motion of the outer halo at the north Galactic pole. The prospects for future debris searches and the implications for the early evolution of the Galaxy are briefly presented.

Peculiar velocity reconstruction with the fast action method: tests on mock redshift surveys

We present extensive tests of the fast action method (FAM) for recovering the past orbits of mass tracers in an expanding universe from their redshift-space coordinates at the present epoch. The tests focus on the reconstruction of present-day peculiar velocities using mock catalogues extracted from high-resolution N-body simulations. The method allows for a self-consistent treatment of redshift-space distortions by direct minimization of a modified action for a cosmological gravitating system. When applied to ideal, volume-limited catalogues, FAM recovers unbiased peculiar velocities with a one-dimensional, 1σ error of ∼220 km s−1, if velocities are smoothed on a scale of 5 h−1 Mpc. Alternatively, when no smoothing is applied, FAM predicts nearly unbiased velocities for objects residing outside the highest density regions. In this second case the 1σ error decreases to a level of ∼150 km s−1. The correlation properties of the peculiar velocity fields are also correctly recovered on scales larger than 5 h−1 Mpc. Similar results are obtained when FAM is applied to flux-limited catalogues mimicking the IRAS PSCz survey. In this case FAM reconstructs peculiar velocities with similar intrinsic random errors, while velocity–velocity correlation properties are well reproduced beyond scales of ∼8 h−1 Mpc. We also show that FAM provides better velocity predictions than other, competing methods based on linear theory or the Zel'dovich approximation. These results indicate that FAM can be successfully applied to presently available galaxy redshift surveys such as IRAS PSCz.

Cometary dust streams at Mars: Preliminary predictions from meteor streams at Earth and from periodic comets

Spacecraft are at risk from impacts of interplanetary dust particles, and those particles are concentrated near the orbits of comets and of meteor streams, which are (for the most part) inferred to derive from comets. To explore potential dangers to Mars‐orbiting spacecraft from cometary dust, we screened known comets and meteor showers for those with orbits that closely approach Mars' orbit. Of the 135 periodic Mars‐crossing comets, the orbits of 50 approach within 0.1 AU of Mars and so are potential current sources of dust and meteor streams at Mars. Among these, IP/Halley, IP/Tempel 1, and 1991D1 P/Hermann seem the most promising targets for further study. Past orbits of all Mars‐crossing comets might also yield meteor streams at Mars. Among known meteor streams, the daytime Arietids and Geminids could produce significant numbers of meteors at Mars but have not produced (so far) meteor storms that could present significant dangers to spacecraft.

On the least action principle in cosmology

Given the present distribution of mass tracing objects in an expanding universe, we develop and test a fast method for recovering their past orbits using the least action principle. In this method, termed FAM for fast action minimization, the orbits are expanded in a set of orthogonal time basis functions satisfying the appropriate boundary conditions at the initial and final times. The conjugate gradient method is applied to locate the extremum of the action in the space of the expansion coefficients of the orbits. The treecode gravity solver routine is used for computing the gravitational field appearing in the action and the potential field appearing in the gradient of the action. The time integration of the Lagrangian is done using Gaussian quadratures. FAM allows us to increase the number of galaxies over previous numerical action principle implementations by more than one order of magnitude. For example, orbits for the similar to 15 000 IRAS PSCz galaxies can be recovered in similar to 12 000 CPU seconds on a 400-MHz DEC-Alpha machine. FAM can recover the present peculiar velocities of particles and the initial fluctuations field. It successfully recovers the flow field down to cluster scales, where deviations of the flow from the Zel'dovich solution are significant. We also show how to recover orbits from the present distribution of objects in redshift space by direct minimization of a modified action, without iterating the solution between real and redshift spaces.

A new tidal model of the Magellanic Stream

view Abstract Citations (29) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A New Tidal Model of the Magellanic Stream Shuter, W. L. H. Abstract This model was devised in an attempt to resolve the discrepancy found between the values for the mass of the Galaxy determined from distant satellites and from the Magellanic Stream. In contrast to previous tidal models, the past orbit of the Magellanic Clouds is not bound to the Galaxy. Instead, they set out in a Hubble flow together with M31 and the Galaxy, were subsequently attracted to M31, and suffered a close (<~60 kpc) collision with it ~6 Gyr ago. The tidal accelerations in this collision projected them back toward the Galaxy and also produced the velocity differentials required to establish the Stream. An attractive feature of this model, which was designed to be compatible with the M31- Galaxy timing argument, is that it provides an explanation for the fact that the plane containing the Galaxy, the Magellanic Clouds, and M31 is close (~24^deg^x) to that of the Magellanic Stream. It also accounts naturally for the high angular momentum of the Magellanic Clouds with respect to the Galaxy. Publication: The Astrophysical Journal Pub Date: February 1992 DOI: 10.1086/170996 Bibcode: 1992ApJ...386..101S Keywords: Astronomical Models; Galactic Mass; Magellanic Clouds; Milky Way Galaxy; Andromeda Galaxy; Galactic Structure; Tides; Astrophysics; CELESTIAL MECHANICS; STELLAR DYNAMICS; GALAXIES: DISTANCES AND REDSHIFTS; GALAXIES: LOCAL GROUP; GALAXIES: MAGELLANIC CLOUDS full text sources ADS | data products SIMBAD (5) NED (3)

The interacting Magellanic System

The Magellanic System is viewed focusing on the global interactions in the System. These give insight into its history and structure. The past orbits of the Magellanic Clouds (MCs) are examined. A tidal encounter between the Large and Small Magellanic Clouds (LMC, SMC) has almost certainly occurred within the last 109 yrs. This hypothesis is supported by the observed structure of the Magellanic System, and so is accepted. The Magellanic Stream is an indirect result of the tidal encounter which is crucial to understanding the Magellanic System. It is a complex interacting gas feature, bifurcated along its entire length with many anomalous velocity H I clouds alongside. The possible models for the Magellanic Stream are examined and here I propose that its origin is due to the collision of a multi-phase halo with the vast region of gas between the LMC and the SMC. In this respect the polar subsystem around our Galaxy is seen to be particularly important. The popular tidal model for the origin of the Magellanic Stream fails to satisfy key observational features, and is thus rejected.

The influence of our Galaxy on the evolution of the Magellanic Clouds

Building upon the assumption of the existence of a hot gaseous corona around the Milky Way Galaxy and a calculation of possible past orbits of the Magellanic Clouds in the gravitational potential of the Galaxy, the question as to whether significant interchange of material could have occurred with the Large Magellanic Cloud is examined. It is estimated that, indeed, the LMC could have exchanged a nontrivial fraction, of the order of 30 percent, of its mass with the corona, over an assumed 10 to the 10th yr of interaction. It therefore follows that, if the Clouds were bound to the Galaxy during the past 10 to the 10th yr, their chemical and dynamical histories would have been strongly influenced by those of the Galaxy itself. It is concluded that either (1) the Clouds have not been bound to the Galaxy over most of its 10 to the 10th yr lifetime, or (2) it is not possible to treat their evolutions as those of isolated systems. 32 refs.

The axial rotation of planets and transfer of mass and angular momentum from a satellite system to its primary

The main topic of this paper is to investigate the exchange of mass and angular momentum between a satellite or planetary system and its primary, and the effects of this exchange to axial rotations and satellite orbits. Various applications on the calculation of axial rotations, present and past satellite masses and orbits and other implications of the theory are presented.

Tidal dissipation in a viscoelastic planet

The rates of energy dissipation in tidally distorted Kelvin‐Voigt, Maxwell, and standard linear solid (SLS) viscoelastic moon models are calculated for a hypothetical past lunar orbit with semimajor axis 34.2 earth radii and obliquity = 49°. Viscosities of 1014 and 1018 Pa s for the Kelvin‐Voigt and Maxwell rheologies, respectively, are needed to match the dissipation rate calculated using the Q approach with a quality factor Q = 100. The SLS model requires a short time viscosity of 3×1017 Pa s to match the Q = 100 dissipation rate independent of the model's relaxation strength. Since Q = 100 is considered a representative value for the interiors of terrestrial planets, the derived viscosities should characterize planetary materials. Neither the Kelvin‐Voigt nor SLS models simulate the behavior of real planetary materials on long timescales. Therefore the significance of the viscosities inferred for these models is unclear. The Maxwell model behaves realistically on both long and short timescales. The inferred Maxwell viscosity, corresponding to a timescale of days, is several orders of magnitude smaller than the longer timescale (≥ 104 years) viscosity of the earth's mantle.

The past orbit of comet Halley and its meteor stream

AbstractThe present paper studies the structural features of the meteor streams associated with Comet Halley deduced from the observations of its meteor showers, as check points of orbital elements in a deeper history of the comet orbit. Libration of the argument of perihelion of the comet and the corresponding displacement of the nodes, as recognized in the distribution of condensations within the stream, allows to estimate the maximum lifetime of the comet in the inner Solar System at about 2 × 105 years.

The Magellanic Stream and its Related Problems

A brief survey is made of recent 21-cm and optical observations of the Magellanic Stream(MS). The space orientation of the Magellanic Clouds is touched upon in relation to modelling the MS. After summarizing a variety of models for the MS, we show that if our Galaxy is massive with a huge dark halo, a tidal model is most suitable for reproducing its characteristic structure and high-negative radial velocity. Past orbits of the Large and the Small Magellanic Cloud (LMC and SMC) are determined uniquely for the last 2×109 yr, if we postulate that the LMC and SMC are bound together for 1010 yr: Highly-noncircular motion of the SMC around the LMC could give a clue to understand some peculiar features associated with the Magellanic Clouds.

The Magellanic Stream: theoretical considerations

The tidal and the primordial theories for the Magellanic Stream are examined in a frame of test-particle simulation for the interacting triple system of the Galaxy, the Large and Small Magellanic Clouds (LMC and SMC). Difficulties of the radial velocity of the Stream still beset these two theories. Several new models for the Stream and the Clouds are briefly discussed in relation to the bending of the galactic disk, the past binary orbits of the LMC and SMC and also the Local Group and the Local Supercluster of galaxies.

Past and future orbit of 1977 UB, object Chiron

Past and future orbit of 1977 UB, object Chiron

A quantitative model of the magnetospheric magnetic field

Quantitative representations of the magnetic fields associated with the magnetopause currents and the distributed currents (tail and quiet time ring currents) have been developed. These fields are used together with a dipole representation of the main field of the earth to model the total vector magnetospheric magnetic field. The model is based on quiet time data averaged over all ‘tilt angle’ values. The weak field in the equatorial region of the inner magnetosphere and the tail field structure are included in the model. The depressed field region in the inner magnetosphere is especially important for the accurate modeling of several observed particle and magnetic field phenomena. The field representation is analytic and is given in Cartesian coordinates with power series and exponential terms. It is valid from the subsolar magnetosphere to beyond lunar orbit. This series expansion allows the magnetic field to be modeled accurately over an extended region of the magnetosphere and permits the representation of the field in the same region as that of its source currents. The model has been tested by using it to calculate several observed magnetospheric particle and field properties. The latitude cutoffs for solar cosmic rays and the trapping boundary of low-energy particles computed from the model agree well with observations. Model calculations also yield field line shapes in agreement with barium cloud observations. A simplified version of the model that can be used out past geosynchronous orbit is also presented.