Family Of Comets Research Articles

Centaurs from the Oort cloud and the origin of Jupiter-family comets

A numerical study of an ensemble of orbits based on observed objects in the near-Neptune high-eccentricity (NNHE) region, with perihelion distances q in the range 28 60 au being roughly an order of magnitude greater than that for a < 60 au, and therefore inconsistent with a source in the NNHE region, which is broadly similar to the so-called ‘Scattered Disc’. The observed distribution of Centaurs with a 60 au is also inconsistent with this source, although it is conceivable that in this region the discrepancies might be explained by factors such as out-gassing, splitting or varying albedo not included in our model. Thus, although Centaurs can be produced from the NNHE region, their numbers and orbital distributions are inconsistent with this region being the dominant source for all Centaurs. We conclude that there must be another source flux, especially for the longer period, more populous group, and suggest that the most likely source for these objects is the Oort cloud. Thus, there are two separate, but overlapping, dynamical classes of Centaurs, one originating from the Oort cloud and the other from the NNHE region. The two source regions produce roughly similar contributions to Centaurs with a 60 au and to the observed Jupiter family of comets.

Polarization studies of comet C/2000 WM1 (LINEAR)

Linear polarization observations were carried out on comet C/2000 WM1 with the 1.2m telescope at Mt. Abu Observatory during November 2001 and March 2002. The observations in November were at low phase angle ($<~22\degr$) when the polarization is negative and where the data for most of the comets are rather meager. The observations during March were made when the phase angle was $\sim$ 47\degr. Observations were conducted through the IHW narrow band and BVR broad band filters. Based on these polarization observations we infer that the comet C/2000 WM1 belongs to high polarization class i.e. the dusty comet family.

Sungrazing Comets Discovered with the SOHO/LASCO Coronagraphs 1996–1998

The Kreutz sungrazing family of comets is unique because of its small perihelion distance and because of the large number of known members of this family. SOHO/LASCO coronagraph observations beginning in 1996 have revealed an unprecedented number of Kreutz comets. These new coronagraph observations improve upon earlier observations because of a larger field-of-view, increased image cadence, and better photometric measurements. This paper presents the lightcurves of the 141 Kreutz family comets observed from 1996 through 1998. Throughout this period, the number of family members discovered each year is shown to be constant. None of the comets were detected postperihelion. The lightcurves show distinctive characteristics which reveal much about the properties of the nuclei. It is shown that the individual fragments can be related to one of two “standard candles,” which we call Universal Curves. The comets all reach a peak brightness at one of two characteristic distances (both near 12 R⊙) and that the comets fragment at another characteristic distance (about 7 R⊙). Also, evidence is seen for line emission, which varies with heliocentric distance.

The young long-period comet family of Saturn

The distributions of long-period comets with respect to the minimum distance Δ between their orbits and the orbit of Saturn or Jupiter, constructed by Konopleva using data up to 1972, exhibit a sharp peak at Δ<0.5 au for the Saturnian family, while being fairly monotonic for Jupiter. Hence, in view of the appreciable eccentricity of Saturn's orbit and the rotation of its perihelion longitude with a period of 47 kyr, the conclusion was drawn by Drobyshevski that the objects belonging to this peak are young (10 kyr). Similar distributions constructed using more recent data show less pronounced differences between one another. Analysis of the distributions for various epochs shows that the initially noted difference is due to observational selection, being inherent to brighter comets. Since on average the cometary activity fades with age, the conclusion that the Saturnian family comets, forming the peak at Δ<0.5 au, are young is all the more substantiated. The question concerning the origin of these comets, which in all likelihood were ejected over a period of a decade from deep inside the Saturnian sphere of influence, is still open. The only self-consistent hypothesis that we see now is that of their appearance as a result of an explosion of the electrolysed ice envelope of Titan. We encourage the development of other explanations.

The Dynamics of Objects in Orbits Resembling That of P/Encke

The overall orbital evolution of bodies resembling that of P/Encke is studied by numerical integration. Dynamical paths are found that connect orbits of this type to their possible sources, i.e., the asteroidal main belt and the Jupiter family of comets. Possible end-states for these orbits include ejection from the region of the inner planets, due to close encounters with Jupiter, and collision with the Sun. We find a purely gravitational dynamical path (i.e., one not involving nongravitational forces) connecting the orbit of P/Encke to the orbits of the rest of the Jupiter family of comets on a timescale of several times 105 years, somewhat longer than typical cometary physical lifetimes. The hypothesis of a genetic relationship among some or all of the bodies currently in Encke-like orbits is not supported by our results. The existence of dynamical channels linking these orbits to asteroidal and cometary sources explains why both types of objects are present in the Taurid complex and points to the presence of both high-density and low-density material in the related meteoroid population.

Statistical trends in cometary magnitude data

The brightness distributions of long-period comets with P > 200 years, and those short-period comets with P < 15 years (Jupiter family of comets) were modelled by Pareto power-law distributions. The models were fitted using maximum likelihood methods and analysed by a new trend analysis approach. The long-period comets were divided into a number of physical parameter ranges, notably by perihelion, inverse semi-major axis and discovery date, and examined for appropriate physical trends. Similarly, the short-period comets were examined for trends and compared with the long-period comets. Overwhelming evidence was found that the brightness indices increase with discovery date for the long-period comets. There was no statistical evidence that the brightness distribution of the long-period comets significantly altered as the 1/ a values decreased. No trends were apparent in the brightness of long-period comets in terms of their perihelion distance for perihelia less than 2.5 a.u.

Comets (Existing Populations)

The definition, population, extent, origin and evolution of the individual subsystems of comets and transitions between them are discussed, together with presentation of the relevant statistical data and their changes with time. The largest outer subsystems are unobservable, but their existence is documented by the necessity of progressive replenishment of the observable populations, with limited survival times. There is persuasive evidence for two different evolutionary paths, one from the Oort cloud and another from the Kuiper belt. While the extent and accuracy of the data available is increasing rapidly, the Jupiter family of comets is the only one for which the evolutionary time scales do not exceed by many orders of magnitude the history of astronomical observations. The individual comet populations differ from one another not only by the distribution of orbits, but also by the size distribution and aging rate of their members. Their dynamical evolution is coupled with disintegration processes, which make it questionable whether the present state can be interpreted as a long-term average.

Mass and orbit estimation of Planet X via a family of comets

The crucial assumption of this paper is, that the observed clustering of aphelion distances of intermediate-period comets in the 70–90 AU range is due to the influence of a tenth planet, called Planet X. We contribute to the search for Planet X a new and extended evaluation of a family of comets assumed to be Planet X's family of comets.

Cometary impacts, molecular clouds, and the motion of the Sun perpendicular to the galactic plane

Raup and Sepkoski1 have presented evidence from marine fossils for a 26-Myr periodicity in the occurrence of mass extinctions. Using the same data Rampino and Stothers2 obtained a different period, 30±1 Myr, which agrees with the 33±3-Myr half-period for the vertical oscillation of the Solar System about the plane of the galaxy3. To explain this agreement they suggest2 that encounters with molecular clouds perturb the Sun's family of comets, causing many to enter the inner Solar System where one or more collide with the Earth; the cloud encounter rate is modulated at twice the oscillation frequency, because the number density of clouds peaks at the galactic plane at the midpoint of the solar oscillation crossed by the Solar System twice per period. Notwithstanding an apparent objection to this that the most recent extinctions are not in phase with the solar oscillation4, their model, given its stochastic nature, can accommodate a few events with large phase discrepancies. The degree of modulation is crucial: it depends on the scale height of the population of molecular clouds relative to the amplitude of the solar motion and tends to zero if this ratio is large and encounters are entirely random. Here we present data from CO surveys of molecular clouds both within and beyond the solar circle, which permit explicit calculation of the strength of the modulation. The cloud layer near the Sun is too extended and, as a consequence, the modulation of cloud encounters is too weak for a statistically significant period to be extracted from the nine extinctions analysed by Rampino and Stothers.

Terrestrial mass extinctions, cometary impacts and the Sun's motion perpendicular to the galactic plane

Episodes of mass extinctions on the Earth are now strongly suspected to be cyclical1. We report here that our analysis of the data of Raup and Sepkoski1 suggests that the dominant cyclicity in major marine mass extinctions during at least the past 250 Myr is 30 ± 1 Myr, with the standard deviation of an individual episode being ±9 Myr. We find this terrestrial cycle to be strongly correlated with the time needed for the Solar System to oscillate vertically about the plane of the Galaxy, which is 33 ± 3 Myr according to the best current astronomical evidence. It is argued that galactic triggering or forcing of terrestrial biological crises may arise as a result of collisions (or close encounters) of the Solar System with intermediate-sized to large-sized interstellar clouds of gas and dust, which are sufficiently concentrated towards the galactic plane to produce the observed cyclicity and its scatter. Among other consequences, a nearby interstellar cloud would gravitationally perturb the Solar System's family of comets and thereby increase the flux of comets and comet-derived bodies near the Earth, leading to large-body impacts. We find a dominant cyclicity of 31 ± 1 Myr in the observed age distribution of impact craters on Earth, the phase of this cycle agreeing with that shown by the major biological crises. Our galactic hypothesis can thus simultaneously account for the mean interval between major terrestrial crises and for the 50% scatter of the time intervals about their mean value.

Families of Periodic Planetary-Type Orbits in the N-Body Problem and Their Application to the Solar System

AbstractA new approach to the study of the Solar System and planetary systems in general is proposed, through the use of periodic planetary-type orbits of the general N-body problem. In such an orbit, one body (called Sun) has a large mass and the rest N-l bodies (called planets) have small but not negligible masses and it can be proved that monoparametric families of periodic orbits of the N-body problem exist in a rotating frame of reference, all being of the planetary type.Two cases are studied in detail, N=3 and N=4. In N=3, apart from a general discussion, we present a detailed analysis of the Sun-Jupiter-Saturn system and a study is made on which configurations with the masses of these two planets, or a multiple of them, are stable or unstable. Also, part of a family is shown to represent the Jupiter family of comets. It was found that commensurabilities are not in general associated with instabilities. For N=4 we present three families of periodic orbits. The motion corresponding to a branch of one of the above families has many similarities with the actual motion of the three inner satellites of Jupiter.It is shown that there exist many commensurable cases in the obtained periodic orbits and that the resonant orbits increase as the number of bodies increases. Based on these results, an attempt is made to explain the existence of commensurabilities in the Solar System.Finally, it is mentioned that a periodic motion of the planetary type can be used as a reference orbit for accurate computations for the actual motions of the planets or satellites of the Solar System. In this way the small divisor difficulties existing in the classical approach will not appear.

The capture of comets

The expression: “Capture of a comet” may lead thoughts primarily to the single encounter mechanism, when a comet happens to pass very close to Jupiter and is at once “captured” into Jupiter’s family of comets, getting an aphelion just outside Jupiter’s orbit, but I would rather suggest that any evolution from a long-period orbit far from the Sun to a short-period orbit, making use of different kinds of perturbations, may be termed a “capture process”, and it is evident that single encounters must play a rather limited role in such evolutions.

Photographic Search for Comets During 12 November Solar Eclispe.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photographic Search for Comets During 12 November Solar Eclispe. Courten, Henry C. ; Genberg, Richard W. Abstract Under NASA grant to Adelphi University a four- man team set up and operated a ground-based photographic station in Bage' in southern Brazil at the centerline of the eclipse path. Specially modified aerial cameras with coverage out to 40 solar radii were used with interference filters and 8 X 10 in. glass plates to search for small bright comets proximate to the sun. Although a high thin atmospheric haze resulted in a rather high level of sky background, star images to mag + 7 were recorded, along with excellent images of the coronal structure. The comet search equipment is a follow-on to the initial search conducted by Dr. B. Donn and Dr. Francois Dossin during the 1963 total eclipse. The most recent effort was enhanced by direct cooperation with Wesleyan University (Van Vleck Observatory) which, under NASA grant, supported an airborne observer with identical photographic equipment. This brief report describes the techniques and equipment used by the Adelphi group. Projection slides exhibit the filter characteristics as matched to the camera lens transmission curve, the equipment erected and ready for field operation, and several sample photographs showing coronal detail. Because of the practical difficulties inherent in reproducing very fine star and comet images artifi- cially enhanced slides of the original negatives are shown. Complete reduction and analysis of the plates is expected to take several more weeks; therefore conclusions on the existence of the family of comets predicted by Dr. P Swings cannot be drawn at this time. Comparison of very recent star plates with those exposed during the eclipse will be accomplished within the next few weeks. Since the earlier stellar images are too faint for blink comparison the simple, yet effective, techniques which are being employed in the analysis are described. Publication: The Astronomical Journal Pub Date: October 1967 DOI: 10.1086/110483 Bibcode: 1967AJ.....72R.791C full text sources ADS |

Gas-Dust Interaction in the Accretion of Interstellar Dust by the Sun.

view Abstract Citations References (4) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Gas-Dust Interaction in the Accretion of Interstellar Dust by the Sun. Stephenson, Charles B. Abstract As is well known, the suggestion that the sun's family of comets was acquired by accretion of dust from the interstellar medium encounters a difficulty in the form of the interaction between dust and radiation pressure. If the general nature of the dust is correctly characterized by current views, the solar radiation pressure upon a particle exceeds the gravitational force for a large fraction of the total population of particles. Hence it is of interest to investigate the possibility that the dust can nevertheless be accreted through interaction with the interstellar gas. Approximate calculations have been made to ascertain the behavior of dust particles of the order of 10- cm in diameter, for which p 1.0, in the radiation field of the sun and subject to viscosity effects in the interstellar gas. It is concluded that interaction between gas and such dust particles cannot compensatefor the influence of radiation pressure for a gas density in the unperturbed cloud < 10 atoms/cm3 and for relative velocities of the order of 5 km/sec between star and cloud Much lower velocities favor dust capture more than do the velocities discussed here, but they involve excessive accretion of gas by the sun. Publication: The Astrophysical Journal Pub Date: July 1957 DOI: 10.1086/146385 Bibcode: 1957ApJ...126..195S full text sources ADS |

Comets and Problems of Cosmogony

THE presidential address at the British Astronomical Association was delivered on October 27 by the Rev. Dr. M. Davidson. He discussed comets, especially in connexion with the light that they throw on problems of cosmogony. Considering that comets move in orbits of such a diverse nature, direct and retrograde orbits being nearly equal in number, taking comets on the whole, he showed that there are difficulties in reconciling this fact with the tidal theory of the origin of the solar system. He referred to the families of comets which are associated with the major planets, stating that it is quite impossible to explain these on the capture theory. There is, he considers, some basis for the view that they were expelled by the planets, though there are certain objections here also. Various theories for the origin of both the short-period and long-period comets were dealt with in turn ; but, Dr. Davidson pointed out, none of these can be considered satisfactory. Bobrovinokoff's conjecture that the sun captured comets when it was passing through diffuse clouds of obscuring matter less than a million years ago would appear to be mere speculation, and great difficulties arise when we inquire how bodies of such diverse sizes as are found in the nuclei of comets should appear in diffuse clouds of obscuring matter. The whole subject is full of difficulties, and Dr. Davidson contented himself with expressing the hope that posterity would be able to solve the problem. At the close of his address, he presented the Walter Goodacre Gold Medal and Gift to Dr. A. C. D. Crommelin, whom the Council selected this year for this award, in consideration of the very valuable work that he has done for the Association, more especially in connexion with comets and minor planets, on which he is a recognized authority.

Our Astronomical Column

THE “CAPTURE THEORY” OF COMETS.—A memoir by M. O. Callandreau, on the capture theory of periodic comets, has recently been published (Annales de l'Observatoire de Paris , vol. xx.). It is generally known that the periodic comets are distributed in groups which depend in some manner on the major planets. Jupiter's family of comets is at least fifteen in number, and all the members of it have direct motion, orbits only slightly inclined to the orbit of Jupiter, and aphelion points near Jupiter's aphelion; what is more—one of the two points where each of them intersects the plane of Jupiter's orbit is generally very near to the trajectory of this planet. The theory which best explains such distribution is that which regards the comets of which the groups are composed as having come under the perturbing influence of the major planet to which they are re spectively related. If a comet arrives from interstellar space into the solar system with a sensible parabolic velocity, and passes near a major planet, the velocity will be either diminished or increased. In the former case, the parabolic orbit would be transformed into an elliptical one, and the comet would be, as it were, incorporated into our system-captured by the planet. If, on the other hand, the velocity is accelerated, the orbit becomes hyperbolic, and the comet moves away from our system, never to return. The results of a research on this subject were given by M. Tisserand a few months ago (Bulletin Astronomique, July 1889, and NATURE, vol. xlii. p. 31).