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1.
The dynamics of larger interplanetary bodies is reviewed, with emphasis on evolutionary problems, interrelations, and open questions. Observational biases distinguishing the sample of known objects from the whole population are briefly discussed. A schematic division of the solar system into zones with different regimes of motion, and a rough taxonomy of orbit types are attempted. The role of individual major planets in controlling the dynamical evolution of interplanetary objects, in particular by stabilizing resonances and destabilizing close encounters, is compared. There are significant evolution asymmetries due to boundary conditions and preferential evolutionary paths; individual major displacements in the phase space of orbital elements conserve the Tisserand invariant with respect to the planet responsible, thus favouring certain evolutionary sequences against others. Very limited lifetimes of some orbit types imply a long-term balance between source and sink, and require a continuous supply of objects from other types of orbits. In this respect, the ultimate fate of extinct comets is of particular interest. Under very specific conditions, nongravitational effects of mass loss can result in stabilization of a formerly unstable orbit. Since the dividing line between the two basic interplanetary populations distinguished by origin and composition — the asteroids and the comets — is essentially that between stable and unstable motion, orbital data can be used to specify which of the known asteroid-like objects may be devolatilized cometary nuclei.Paper presented at the European Workshop on Planetary Sciences, organised by the Laboratorio di Astrofisica Spaziale di Frascati, and held between April 23–27, 1979, at the Accademia Nazionale del Lincei in Rome, Italy.  相似文献   

2.
Ignacio Ferrín 《Icarus》2006,185(2):523-543
We present the secular light curve (SLC) of 133P/Elst-Pizarro, and show ample and sufficient evidence to conclude that it is evolving into a dormant phase. The SLC provides a great deal of information to characterize the object, the most important being that it exhibits outburst-like activity without a corresponding detectable coma. 133P will return to perihelion in July of 2007 when some of our findings may be corroborated. The most significant findings of this investigation are: (1) We have compiled from 127 literature references, extensive databases of visual colors (37 comets), rotational periods and peak-to-valley amplitudes (64 comets). 2-Dimensional plots are created from these databases, which show that comets do not lie on a linear trend but in well defined areas of these phase spaces. When 133P is plotted in the above diagrams, its location is entirely compatible with those of comets. (2) A positive correlation is found between cometary rotational periods and diameters. One possible interpretation suggest the existence of rotational evolution predicted by several theoretical models. (3) A plot of the historical evolution of cometary nuclei density estimates shows no trend with time, suggesting that perhaps a consensus is being reached. We also find a mean bulk density for comets of 〈ρ〉=0.52±0.06 g/cm3. This value includes the recently determined spacecraft density of Comet 9P/Tempel 1, derived by the Deep Impact team. (4) We have derived values for over 18 physical parameters, listed in the SLC plots, Figs. 6-9. (5) The secular light curve of 133P/Elst-Pizarro exhibits a single outburst starting at +42±4 d (after perihelion), peaking at LAG=+155±10 d, duration 191±11 d, and amplitude 2.3±0.2 mag. These properties are compatible with those of other low activity comets. (6) To explain the large time delay in maximum brightness, LAG, two hypothesis are advanced: (a) the existence of a deep ice layer that the thermal wave has to reach before sublimation is possible, or (b) the existence of a sharp polar active region pointing to the Sun at time = LAG, that may take the form of a polar ice cap, a polar fissure or even a polar crater. The diameter of this zone is calculated at ∼1.8 km. (7) A new time-age is defined and it its found that T-AGE = 80 cy for 133P, a moderately old comet. (8) We propose that the object has its origin in the main belt of asteroids, thus being an asteroid-comet hybrid transition object, an asteroidal belt comet (ABC), proven by its large density. (9) Concerning the final evolutionary state of this object, to be a truly extinct comet the radius must be less than the thermal wave depth, which at 1 AU is ∼250 m (at the perihelion distance of 133P the thermal wave penetrates only ∼130 m). Comets with radius larger than this value cannot become extinct but dormant. Thus we conclude that 133P cannot evolve into a truly extinct comet because it has too large a diameter. Instead it is shown to be entering a dormant phase. (10) We predict the existence of truly extinct comets in the main belt of asteroids (MBA) beginning at absolute magnitude ∼21.5 (diameter smaller than ∼190 m). (11) The object demonstrates that a comet may have an outburst of ∼2.3 mag, and not show any detectable coma. (12) Departure from a photometric R+2 law is a more sensitive method (by a factor of 10) to detect activity than star profile fitting or spectroscopy. (13) Sufficient evidence is presented to conclude that 133P is the first member of a new class of objects, an old asteroidal belt comet, ABC, entering a dormant phase.  相似文献   

3.
《Icarus》1987,69(1):33-50
Spectrophotometric data on groups of asteroids in different types of orbits reveal different distributions of spectral properties, depending on whether the orbits are cometary or noncometary. In a list of 10 asteroids frequently suggested on purely dynamical grounds to be extinct or dormant comets, all have properties suggestive of spectral classes D, P, or C. Preliminary IRAS albedo results support this. Objects in these classes are very dark, reddish-black to neutral-black, and prevalent among the Trojans and outer belt. Two comets observed at low activity (visible nuclei) also have properties more consistent with D asteroids than any other class (very low reported geometric albedos of 0.02 and red colors). Consistent with these results are very low albedos reported for materials in more than a dozen comets; they average 0.05. Also, sampled cometary dust particles appear to consist of dark carbonaceous materials. Dramatically different are a control group of 13 Aten/Apollo/Amor objects selected from noncometary orbits. Most are in moderate-albedo classes: 8 or 9 appear to be of class S, and only 1 is in a low-albedo class (C). These are probably mostly objects perturbed out of the inner asteroid belt. The preponderence of S's in the noncometary group, together with the preponderence of ordinary chondrites among meteorites, may be evidence that such meteorites came from S asteroids. The data indicate that extinct, dormant, inactive, and minimally active comet nuclei have low albedos (pv=a few percent) and very red to moderately red colors. As a group, their spectra are more similar to those of outer Solar System asteroids of classes D, P, and C, than to those of inner belt classes, though the observations are frequently not yet complete enough to assign definitively a spectral class. The results, taken together, support the view that dynamically identified “extinct comet candidates” are indeed outer Solar System objects probably of cometary origin. The results also support a scenario of Solar System formation in which dark carbonaceous dust dominated the spectrophotometric properties of planetesimals formed from about 2.7 AU out to at least the Trojan region at 5.2 AU. From 2.7 to at least 5.2 AU, and from class C to class D, the color of this dust reddens, apparently due to increasing amounts of red organic condensates. Comets are probably also colored to different degrees, by dust of this type, and may in some cases be even redder than D asteroids.  相似文献   

4.
Direct observations of the nuclear surfaces of comets have been difficult; however a growing number of studies are overcoming observational challenges and yielding new information on cometary surfaces. In this review, we focus on recent determinations of the albedos, reflectances, and thermal inertias of comet nuclei. There is not much diversity in the geometric albedo of the comet nuclei observed so far (a range of 0.025 to 0.06). There is a greater diversity of albedos among the Centaurs, and the sample of properly observed TNOs(2) is still too small. Based on their albedos and Tisser and invariants, Fernández et al. (2001) estimate that about 5% of the near-Earth asteroids have a cometary origin, and place an upper limit of 10%. The agreement between this estimate and two other independent methods provide the strongest constraint to date on the fraction of objects that comets contribute to the population of near-Earth asteroids. There is a diversity of visible colors among comets, extinct comet candidates, Centaurs and TNOs. Comet nuclei are clearly not as red as the reddest Centaurs and TNOs. What Jewitt (2002) calls ultra-red matter seems to be absent from the surfaces of comet nuclei. Rotationally resolved observations of both colors and albedos are needed to disentangle the effects of rotational variability from other intrinsic qualities. New constraints on thermal inertia of comets are consistent with previous independent estimates. The thermal inertia estimates for Centaurs 2060 Chiron and 8405 Asbolus are significantly lower than predicted by thermal models, and also lower than the few upper limits or constraints known for active, ordinary nuclei.  相似文献   

5.
We have examined the effects of vaporization from the nucleus of a comet and show that a latitude dependence of vaporization can, in some cases, explain asymmetries in cometary light curves. We also find that a non-uniform distribution of solar radiation over a comet can considerably shorten the vaporization lifetime compared to the results normally obtained by assuming that the nuclear surface is isothermal.Independent of any latitude effects, comets with CO2-dominated nuclei and with perihelion distances less than 0.5 AU have vaporization lifetimes less than or comparable to their dynamical ejection times. This may explain the observed deficit of comets with small perihelion distances. Similarly comets with CO2-dominated nuclei and perihelia near Jupiter's orbit have vaporization lifetimes that are shorter than the time for capture into short-period orbits. We suggest, therefore, that at least some new comets are composed in large part of CO2, while only H2O-dominated comets, with lower vaporization rates, can survive to be captured into short-period orbits.  相似文献   

6.
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.  相似文献   

7.
Abstract— Absolute and relative cratering rates on the terrestrial planets have been calculated using the same asteroidal collision model and Monte Carlo program used for previous studies of the terrestrial meteorite flux, the steady-state number of Apollo-Amor objects, and the orbital distribution of both meteorites and Apollo-Amor objects. The most straightforward result is that projectiles from the asteroid belt appear to provide about one-third the observed present-day production of terrestrial craters larger than 10 km in diameter. When uncertainties in the calculations and observations are included, it cannot be excluded that the entire terrestrial cratering flux is asteroidal. On the other hand, assumption of an additional Apollo-Amor source of extinct comets, in the same quantity permitted by Apollo-Amor observations, provides better agreement with the observed cratering rate. In addition, a significant (e.g., ～30%) terrestrial contribution from active long and short period comets is acceptable within the uncertainties of the assumptions required. The ratios of the cratering rates on the different terrestrial planets are somewhat sensitive to the assumed source. A purely asteroidal source predicts a martian cratering rate per unit area about four times that on Earth, whereas the difference is reduced to about a factor of two for the mixed asteroid-extinct comet source. The opposite effect is found for Mercury. As discussed by previous authors, the predicted lunar cratering rate is significantly higher than that observed. It is not clear whether this is a result of scaling to impacts on a body considerably smaller than Earth, or if it indicates an increase in the cratering flux during the Phanerozoic.  相似文献   

8.
《Icarus》1987,70(2):269-288
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.  相似文献   

9.
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.  相似文献   

10.
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.  相似文献   

11.
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.  相似文献   

12.
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.  相似文献   

13.
《Icarus》1986,65(1):37-50
In the planet X model periodic comet showers are associated with passages of the planet's perihelion and aphelion points through a primordial disk of comets believed to lie beyond the orbit of Neptune. A strong feature of this model is that the required orbital elements and mass of planet X are consistent with independently predicted values based on the residuals in the motions of Uranus and Neptune. Here we present a more extensive analysis of the model taking into account the fact that only those comets scattered directly into the zones of influence of Saturn and Jupiter can contribute to a shower whose duration is consistent with observation (≲ 15 myr). These requirements impose a minimum planetary inclination of ≈25°, which in turn restricts the semimajor axis to be ≲100 AU. A fraction of the comets scattered directly into the zones of influence of Uranus and Neptune will evolve on time scales of ∼108 years into the steady state flux of short-period comets. We find that the absolute numbers of shower and steady state are comparable and compatible with the known terrestrial cratering rate, assuming the existence of long-lived extinct comet cores. Canonical planet X model parameters, deduced in part from the scattering dynamics analysis, are: semimajor axis ≈80 AU, eccentricity ≈0.3, inclination ≈45°, and mass ≈5m⊕. An analysis is given which suggests that planet X, in its present orbit, can create the requisite density gradient of comets near perihelion and aphelion during the lifetime of the Solar System. The required inclination of planet X's orbit (≳25°) may explain the failure of previous surveys to discover the planet as its present latitude is not likely to be near the ecliptic. It it exists, the best immediate hope of finding planet X is the ongoing IRAS search in the 100-μm band and the full sky optical survey by Shoemaker and Shoemaker. Independent of the question of periodic comet showers, the existence of planet X and the comet disk can readily explain the origin of the steady state flux of short-period comets over a wide range of parameters.  相似文献   

14.
We present new visible and near-infrared spectroscopic measurements for 252 near-Earth (NEO) and Mars-crossing (MC) objects observed from 1994 through 2002 as a complement to the Small Main-Belt Asteroid Spectroscopic Survey (SMASS, http://smass.mit.edu/). Combined with previously published SMASS results, we have an internally consistent data set of more than 400 of these objects for investigating trends related to size, orbits, and dynamical history. These data also provide the basis for producing a bias-corrected estimate for the total NEO population (Stuart and Binzel, 2004, Icarus 170, 295-311). We find 25 of the 26 Bus (1999, PhD thesis) taxonomic types are represented, with nearly 90% of the objects falling within the broad S-, Q-, X-, and C-complexes. Rare A- and E-types are more common in the MC than NEO population (about 5% compared to <1%) and may be direct evidence of slow diffusion into MC orbits from the Flora and Hungaria regions, respectively. A possible family of MC objects (C-types) may reside at the edge of the 5:2 jovian resonance. Distinct signatures are revealed for the relative contributions of different taxonomic types to the NEO population through different source regions. E-types show an origin signature from the inner belt, C-types from the mid to outer belt, and P-types from the outer belt. S- and Q-types have effectively identical main-belt source region profiles, as would be expected if they have related origins. A lack of V-types among Mars-crossers suggests entry into NEO space via rapid transport through the ν6 and 3:1 resonances from low eccentricity main-belt orbits, consistent with a Vesta origin. D-types show the strongest signature from Jupiter family comets (JFC), with a strong JFC component also seen among the X-types. A distinct taxonomic difference is found with respect to the jovian Tisserand parameter T, where C-, D-, and X-type (most likely low albedo P-class) objects predominate for T?3. These objects, which may be extinct comets, comprise 4% of our observed sample, but their low albedos makes this magnitude limited fraction under-representative of the true value. With our taxonomy statistics providing a strong component to the diameter limited bias correction analysis of Stuart (2003, PhD thesis), we estimate 10-18% of the NEO population above any given diameter may be extinct comets, taking into account asteroids scattered into T<3 orbits and comets scattered into T>3 orbits. In terms of possible space weathering effects, we see a size-dependent transition from ordinary chondrite-like (Q-type) objects to S-type asteroids over the size range of 0.1 to 5 km, where the transition is effectively complete at 5 km. A match between the average surface age of 5 km asteroids and the rate of space weathering could constrain models for both processes. However, space weathering may proceed at a very rapid rate compared with collisional timescales. In this case, the presence or absence of a regolith may be the determining factor for whether or not an object appears “space weathered.” Thus 0.1 to 5 km appears to be a critical size range for understanding the processes, timescales, and conditions under which a regolith conducive to space weathering is generated, retained, and refreshed.  相似文献   

15.
We present results of polarimetric and photometric observations of bright comet C/1995 O1 (Hale-Bopp) obtained at the 0.7 m telescope of Kharkov University Observatory from June 18, 1996 to April 24, 1997. The IHW and HB comet filters were used. The C2 and C3 production rates for Hale-Bopp are more than one order of magnitude larger and the dust production rates are more than two orders of magnitude larger than the Halley ones at comparable distances. Hence, Hale-Bopp was one of the most dusty comets. The average UC-BC and BC-RC colours of the dust were −0.02 and 0.13 mag, respectively. The polarization of comet Hale-Bopp at small phase angles of 4.8–13.0° was in good agreement with the date for comet P1/Halley at the same phase angles in spite of the fact that the heliocentric distances of comments differed nearly twice. However, at intermediate phase angles of 34–49° the polarization of comet Hale-Bopp was significantly larger than the polarization of the other dusty comets. It is the first case of such a large difference found in the continuum polarization of comets. The wavelength dependence of polarization for Hale-Bopp was steeper than for other dusty comets. The observed degree of polarization for the anti-sunward side of the coma was permanently higher than that for the sunward shell side. The polarization phase dependence of Hale-Bopp is discussed and compared with the polarization curves for other dusty comets. The peculiar polarimetric properties of comet Hale-Bopp are most likely caused by an over-abundance of small or/and absorbing dust particles in the coma. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

16.
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17.
Effects of collisions with interplanetary particles are investigated. To this purpose, collision probabilities for comets with different orbital elements are computed. It is found that collisions may have a non-negligible effect on the physical evolution of comets. In this connection, it is shown that under certain conditions collisional lifetimes may be shorter than dynamical or vaporization lifetimes. In particular, collisional lifetimes are on average shorter for comets in retrograde orbits than those for direct ones. It is further suggested that catastrophic collisions may contribute to prevent long-period comets in retrograde orbits from reaching short-period orbits by orbital diffusion. Collisions may also produce irregularities of the nucleus brightness by leaving exposed regions of fresh volatile material and may in this way lead to a rejuvenation of old dusty short-period comets. Catastrophic collision probabilities are too low to account for the observed comet splittings, so other trigger mechanisms should be at work. However, it is shown that collisional mini-bursts (increases in brightness of one magnitude or so) caused by decimeter-sized bodies may occur rather frequently on short-period comets when they pass through the asteroid belt. The burst observed in comet Tempel-2 at 3 AU in December, 1978 could be an example of such collisional mini-bursts. The systematic observation of periodic comets when they pass through the asteroid belt could give valuable information about the spatial density of decimeter and meter-sized bodies. In particular, collisional effects for comet Halley, for which a continuous surveillance is planned, are evaluated.  相似文献   

18.
《Icarus》1987,71(1):46-56
The effect of close stellar encounters in modulating the influx rate of Oort cloud comets is investigated. In particular, it is shown that comet showers intense enough to be reflected in crater statistics can be produced at intervals of 80 million years or so, provided we are dealing with an Oort cloud consisting of a heavy core of comets. In this case, there is found a strong predominance of incoming comets from the sky zone where the perturbing star makes its closest approach. We have also performed numerical simulations of the time evolution of comet showers or bursts. From this numerical study, a long tail of residual shower comets is found to follow the major event with an intensity (as compared with the intensity of the shower as its peak) of ∼10−2 after 20—30 million years. Our results thus suggest that residual shower comets may be clustered mainly on certain sky areas and observable at practically any time given the lasting effects of a shower. This might explain some of the observed clustering of aphelion points of long-period comets.  相似文献   

19.
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.  相似文献   

20.
We observed 34 comets using the 24 μm camera on the Spitzer Space Telescope. Each image contains the nucleus and covers at least 106 km of each comet's orbit. Debris trails due to mm-sized or larger particles were found along the orbits of 27 comets; 4 comets had small-particle dust tails and a viewing geometry that made debris trails impossible to distinguish; and only 3 had no debris trail despite favorable observing conditions. There are now 30 Jupiter-family comets with known debris trails, of which 22 are reported in this paper for the first time. The detection rate is >80%, indicating that debris trails are a generic feature of short-period comets. By comparison to orbital calculations for particles of a range of sizes ejected over 2 yr prior to observation, we find that particles comprising 4 debris trails are typically mm-sized while the remainder of the debris trails require particles larger than this. The lower-limit masses of the debris trails are typically 1011 g, and the median mass loss rate is 2 kg/s. The mass-loss rate in trail particles is comparable to that inferred from OH production rates and larger than that inferred from visible-light scattering in comae.  相似文献   

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