On the hypothesis of the genetic connection of comets with Pluto and the transneptunian object 2003 UB 313

The hypothesis suggested by Guliev on transneptunian objects as sources of comets is considered. The motion equations for 137 near-parabolic comets over a time interval of 5000 years were numerically integrated. No interaction between 78 comets and the transneptunian object 2003 UB 313 has been revealed: the comets were farther than 3 AU from it. It has been shown that 59 comets—candidates to Pluto’s family-approached Pluto at a distance larger than 0.7 AU. The fulfilled analysis allows us to conclude that Guliev’s hypothesis on transneptunian objects as sources of comets is groundless.     

Collision with meteoroids as one of the possible mechanisms for the splitting of cometary nuclei

Results are presented of a statistical analysis of dynamic parameters for 114 comets with split nuclei. A list of the objects includes actually split comets, fragments of cometary pairs, lost comets with designation D, and comets with large-scale atmospheric features. Some aspects of the hypothesis that splitting is caused by collisions of cometary nuclei with meteoroid swarms are investigated. To verify the hypothesis, an analysis is conducted of the positions of split comets’ orbits relative to 58 meteor streams from Cook’s catalogue. The calculations give the number (N) of orbital nodes of split comets relative to the plane of each swarm within a distance of 0.001, 0.005, 0.01, 0.05, and 0.1 AU from each swarm. A special algorithm is proposed for determining the degree of redundancy of N by finding the expected value and dispersion for the number of the nodes. The comparison of N with the expected value, together with the consideration of the dispersion, reveals a redundancy of N in 29 cases. Therefore, collisions of comets with meteoroid swarms can be considered as one of the possible causes of comet splitting. A similar testing is conducted for the asteroid belt and Kuiper belt as potential sources of a vast number of sporadic meteoroids. Based on the results of the calculations, the former may be considered as the most effective region of splitting of periodic comets.     

On the hypothesis of the eruption origin of near-parabolic comets

The hypothesis on the genetic connection of near-parabolic comets with Jupiter, Saturn, and the transPlutonian region (5–3000 AU) proposed by E.M. Drobyshevskii is considered. It has been shown that, on average, 5.6 comets per an area of 10⁶ AU² passed through the transPlutonian region during the whole history of observations. Six-hundred nineteen comets crossed the ecliptic at heliocentric distances ranging from 0 to 2 AU. As has been shown, from the total number of 945 near-parabolic comets, eight comets closely approached Jupiter and five closely approached Saturn. The Kreutz comets, 1277 objects, did not approach Jupiter closer than 3 AU. Their minimal distance to Saturn was 5.5 AU. The minimal distance of the Kreutz comets from the edge of the transPlutonian region was 28.8 AU. The analysis led to the conclusion that the concept on the origin of the near-parabolic comets suggested by Drobyshevskii is groundless.     

On the actual existence of the periodic and long-period comet families of Uranus

Aphelion distances of the known periodic comets in the range 12–26 AU are analyzed. The aphelia of 12 of the 38 known comets are found to be concentrated at 19.23–20.91 AU, i.e., near the heliocentric distance of Uranus, which seems unlikely to be a coincidence. It is shown by testing that there is also a significant redundancy of distant nodes of the periodic comets’ orbits in the region of motion of Uranus. This is confirmed by the analysis of the MOIDs in the comet-Uranus system. The values of the Tisserand constant for some of the comets exhibit less dispersion relative to Uranus than to Saturn, Jupiter, and the Earth. We selected 20 long-period comets with distant nodes near the region of motion of Uranus. It is shown that, given a uniform spatial distribution, there must be 12 such nodes. Considering the distant nodes and the MOIDs, the planet is likely to have a dynamical connection with the selected group of comets. The distant nodes and perihelia of both periodic and long-period comets are found to be redundant in the directions 76° and 256°, which is qualitatively consistent with the hypothesis of eruptive origin of comets.     

Transneptunian object 2003 UB 313 as a source of comets

The possibility of interrelation between long-period comets and 2003 UB 313, a recently discovered large Kuiper Belt body, is investigated. For this purpose, 78 objects crossing the plane of motion of this body at distances from 37.8 to 97.6 AU have been selected from 860 long-period comets. The overpopulation of comets with this characteristic is also considered. The plane of motion of 2003 UB 313 is compared with the orbital planes of other objects in number of comet crossings in the specified distance interval or in some parts of it. A statistically significant overpopulation of elliptic and intermediate comets with the corresponding orbital nodes has been established. Recently discovered and absolutely faint comets show the best effect in this sense. The same is also true for comets with osculating eccentricities e < 1. A similar result is also obtained for comets with “original” a ^?1 > 0.010000. It is hypothesized that the 2003 UB 313 family is present among the 78 comets. Four of them have aphelion distances from 37.8 to 97.6 AU. An ellipticity is traceable in the distribution of some of the 78 distant nodes. This may be considered as a further argument for the suggested hypothesis. Generally, the body 2003 UB 313 may be assumed to play a prominent role in injecting observable comets from the transneptunian region     

The origin of the CN radical in comets: A review from observations and models

The origin of CN radicals in comets is not completely understood so far. We present a study of CN and HCN production rates and CN Haser scale lengths showing that: (1) at heliocentric distances larger than 3 AU, CN radicals could be entirely produced by HCN photolysis; (2) closer to the Sun, for a fraction of comets CN production rates are higher than HCN ones whereas (3) in the others, CN distribution cannot be explained by the HCN photolysis although CN and HCN production rates seem to be similar. Thus, when the comets are closer than 3 AU to the Sun, an additional process to the HCN photolysis seems to be required to explain the CN density in some comets.The photolysis of HC₃N or C₂N₂ could explain the CN origin. But the HC₃N production rate is probably too low to reproduce CN density profile, even if uncertainties on its photolysis leave the place for all possible conclusions. The presence of C₂N₂ in comets is a reliable hypothesis to explain the CN origin; thus, its detection is a challenging issue. Since C₂N₂ is very difficult to detect from ground-based observations, only in situ measurements or space observations could determine the contribution of this compound in the CN origin.Another hypothesis is a direct production of CN radicals by the photo- or thermal degradation of complex refractory organic compounds present on cometary grains. This process could explain the spatial profile of CN inside jets and the discrepancy noted in the isotopic ratio ¹⁴N/¹⁵N between CN and HCN. Laboratory studies of the thermal and UV-induced degradation of solid nitrogenated compounds are required to model and validate this hypothesis.     

Comets – A Vehicle for Panspermia

Arguments are given for life being a cosmic phenomenon. The physical and chemical conditions associated with comets favour the hypothesis that comets carry, amplify and disperse life throughout the universe. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Does a continuous solid nucleus exist in comets

The implication of actual cometary observations for the physical nature of comets is briefly reviewed and brings out the complete conflict with observation of the ice-dust solid nucleus model put forward in recent years as representing the fundamental structure of comets. That under increasing solar heat the nucleus develops an expanding atmosphere is incosistent with the well-established phenomenon that the comacontracts with decreasing distance from the Sun. Several comets remaining always beyond Mars have nevertheless been strongly active and produced fine tails. The some comets show at times a star-like point of light is readily explicable on the dust-cloud structure and by no means establishes that a solid nucleus exists. With the nucleus-area corresponding not to a small solid mass but to an optical phenomenon, there would be no reason to expect that it would describe a precise dynamical orbit. On the hypothesis of a nucleus, it is necessary to postulate further some internal jet-propulsion mechanism to account for the orbital deviations.In planning a space-mission to a comet, and if search for a nucleus is included, it will be of the highest importance for its success to ensure beforehand that the equipment carried with not fail to discover a kilometric-sized body if one is present, otherwise a null result could be interpreted simply as a failure of this part of the mission and not a proving the absence of any nucleus.     

An examination of an interstellar hypothesis for the source of comets

The Sun's gravity tends to pull in nearby an excess of low-energy particles, as compared with the distribution of energies at infinity. The size of this effect is calculated in an attempt to determine if it is large enough to lend support to the hypothesis of an interstellar origin for comets. The effect appears to be too small; the greatest possible reduction of observed mean energy below intrinsic mean energy is a factor $\text{1}\text{2}$, if the true velocity distribution of the particles (comets) at infinity is Maxwellian. Non-Maxwellian distributions, however, could violate this restriction.     

Periodic variation of Oort Cloud flux and cometary impacts on the Earth and Jupiter

Time variation in impact probability is studied by assuming that the periodic flux of the Oort Cloud comets within 15 au arises from the motion of the Sun with respect to the Galactic mid-plane. The periodic flux clearly shows up in the impact rate of the captured Oort Cloud cometary population, with a phase shift caused by the orbital evolution. Depending on the assumed flux of comets and the size distribution of comets, the impact rate of the Oort Cloud comets of 1 km in diameter or greater is from 5 to 700 impacts Myr⁻¹ on the Earth and from 0.5 to 70 impacts per 1000 yr on Jupiter. The relative fractions of impacts are 0.09, 0.11, 0.26 and 0.54 for long-period comets, Halley type comets, Jupiter family comets and near-Earth objects, respectively. For Jupiter, the corresponding fractions in the first three categories are 0.18, 0.31 and 0.51. If we consider physical fading of comet activity that is compatible with the observations, then the impact rates of active comets are two orders of magnitude smaller than the total impact rates by all kinds of comets and cometary asteroids of size 1 km or greater.     

Long-term evolution of Oort Cloud comets: capture of comets

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 non-gravitational 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.     

Relationship of comets and planets

We analyze our earlier data on the numerical integration of the equations of motion for 274 short-period comets (with the period P<200 yr) on a time interval of 6000 yr. As many as 54 comets had no close approaches to planets, 13 comets passed through the Saturnian sphere of action, and one comet passed through the Uranian sphere of action. The orbital elements of these 68 comets changed by no more than ±3 percent in a space of 6000 yr. As many as 206 comets passed close to Jupiter. We confirm Everhart’s conclusion that Jupiter can capture long-period comets with q = 4–6 AU and i < 9° into short-period orbits. We show that nearly parabolic comets cross the solar system mainly in the zone of terrestrial planets. No relationship of nearly parabolic comets and terrestrial planets was found for the epoch of the latest apparition of comets. Guliev’s conjecture about two trans-Plutonian planets is based on the illusory excess of cometary nodes at large heliocentric distances. The existence of cometary nodes at the solar system periphery turns out to be a solely geometrical effect.     

On the absence of an interrelation between cometary orbits and Pluto

A hypothesis on the origin of comets in the system of Pluto has been considered. It has been shown that none of the 59 near-parabolic comets—candidates for Pluto’s family—passed through the sphere of its influence in the time interval from 2000 to −3000.     

Capture of comets from the Oort cloud into Halley-type and Jupiter-family orbits

This paper analyzes the capture of comets into Halley-type and Jupiter-family orbits from the nearparabolic flux of the Oort cloud. Two types of capture into Halley-type orbits are found. The first type is the evolution of near-parabolic orbits into short-period orbits (with heliocentric orbital periods P < 200 years) as a result of close encounters with giant planets. This process is followed by a very slow drift of cometary orbits into the inner part of the Solar System. Only those comets may pass from short-period orbits into Halley-type and Jupiter-family orbits, which move in orbits with perihelion distances q < 13 au. In the second type of capture, the perihelion distances of cometary orbits become rather small (< 1.5 au) during the first stage of dynamic evolution under the action of perturbations from the Galaxy, and then their semimajor axes decrease as a result of diffusion. The capture takes place, on average, in 500 revolutions of the comet about the Sun, whereas in the first case, the comet is captured, on average, after 12500 revolutions. The region of initial orbital perihelion distances q > 4 au is found to be at least as important a source of Halley-type comets as the region of perihelion distances q < 4 au. More than half of the Halley-type comets are captured from the nearly parabolic flux with q > 4 au. The analysis of the dynamic evolution of objects moving in short-period orbits shows that the distribution of Centaurs orbits agrees well with the observed distribution corrected for observational selection effects. Hence, the hypothesis associating the origin of Centaurs with the Edgeworth-Kuiper belt and the trans-Neptunian region exclusively should be rejected.     

From the Oort cloud to observable short-period comets – I. The initial stage of cometary capture

We investigate the first stage of the dynamical evolution of Oort cloud comets entering the planetary region for the first time. To this purpose, we integrate numerically the motions of a large number of fictitious comets pertaining to two samples, both with perihelion distances up to 5.7 au and random inclinations; the first sample is composed of comets whose orbits have at least one node close to 5.2 au, while the second is not subject to this constraint. We examine the orbits when the comets come to aphelion after their first perihelion passage within the planetary region, and find that there is a clear statistical dependence of the energy perturbations on the Tisserand parameter. There appear to be two main processes, of comparable importance, governing the shortening of semimajor axes to values of less than 1000 au, i.e. planetary close encounters, especially with Jupiter, and indirect perturbations due to the shifting of the motion from barycentric to heliocentric and back; the former process mostly affects comets crossing the ecliptic at about 5.2 au, or on low-inclination orbits, while the latter mostly affects comets of small perihelion distance. This last result may help to understand the relative paucity of Halley-type comets with perihelion distances larger than about 1.5 au.     

Star passages through the Oort cloud

Stars passing through the Oort cloud eject comets to interstellar space and initiate showers of comets into the planetary region. Monte Carlo simulations of such passages are performed on a representative distribution of cometary orbits. Ejected comets generally lie along a narrow tunnel “drilled” by the star through the cloud. However, shower comets come from the entire cloud, and do not give a strong signature of the star's passage, except in the inverse semimajor axis distribution for the shower comets. The planetary system is likely not experiencing a cometary shower at this time.     

Young Meteor Swarms Near the Sun: I. Statistical Correlation of Meteors with Families of Short-Perihelion Comets

We examine the hypothesis about the formation of meteor streams near the Sun. Families of short-perihelion orbit comets, many of which pass just a few radii from the solar surface at perihelion and have high dust production efficiencies, are assumed to be candidates for the parent bodies of these meteor streams. Our statistical analysis of orbital and kinematic parameters for short-perihelion meteoric particles recorded at the Earth and comets from the Kreutz family and the Marsden, Kracht, and Meyer groups led us to certain conclusions regarding the proposed hypothesis. We found a correlation between the ecliptic longitude of perihelion for comet and meteor orbits and the perihelion distance. This correlation may be suggestive of either a genetic connection between the objects of these two classes or the result of an as yet unknown mechanism that equally acts on short-perihelion comet and meteor orbits. A reliable conclusion about this genetic connection can be reached for the meteors that belong to the Arietids stream and the Marsden comet group.     

Long-Period Comets and the Oort Cloud

Long-period (LP) comets, Halley-type (HT) comets, and even some comets of the Jupiter family, probably come from the Oort cloud, a huge reservoir of icy bodies that surrounds the solar system. Therefore, these comets become important probes to learn about the distant Oort cloud population. We review the fundamental dynamical properties of LP comets, and what is our current understanding of the dynamical mechanisms that bring these bodies from the distant Oort cloud region to the inner planetary region. Most new comets have original reciprocal semimajor axes in the range2 × 10^-5 < 1/a_orig < 5 × 10^-5AU^-1. Yet, this cannot be taken to represent the actual space distribution of Oort cloud comets, but only the region in the energy space in which external perturbers have the greatest efficiency in bringing comets to the inner planetary region. The flux of Oort cloud comets in the outer planetary region is found to be at least several tens times greater than the flux in the inner planetary region. The sharp decrease closer to the Sun is due to the powerful gravitational fields of Jupiter and Saturn that prevent most Oort cloud comets from reaching the Earth’s neighborhood (they act as a dynamical barrier). A small fraction of ～10^-2 Oort cloud comets become Halley type (orbital periods P < 200 yr), and some of them can reach short-period orbits with P < 20 yr. We analyze whether we can distinguish the latter, very ‘old” LP comets, from comets of the Jupier family coming from the Edgeworth-Kuiper belt.     

The frequency and intensity of comet showers from the Oort cloud

We simulate the Oort comet cloud to study the rate and properties of new comets and the intensity and frequency of comet showers. An ensemble of ∼10⁶ comets is perturbed at random times by a population of main sequence stars and white dwarfs that is described by the Bahcall-Soneira Galaxy model. A cloning procedure allows us to model a large ensemble of comets efficiently, without wasting computer time following a large number of low eccentricity orbits. For comets at semimajor axis a = 20,000 AU, about every 100 myr a star with mass in the range 1M_⊙−2M_⊙ passes within ∼10,000 AU of the Sun and triggers a shower that enhances the flux of new comets by more than a factor of 10. The time-integrated flux is dominated by the showers for comets with semimajor axes less than ∼30,000 AU. For semimajor axes greater than ∼30,000 AU the comet loss rate is roughly constant and strong showers do not occur. In some of our simulations, comets are also perturbed by the Galactic tidal field. The inclusion of tidal effects increases the loss rate of comets with semimajor axes between 10,000 and 20,000 AU by about a factor of 4. Thus the Galactic tide, rather than individual stellar perturbations, is the dominant mechanism which drives the evolution of the Oort cloud.