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1.
We analyze the Centaur population as a group of objects with perihelion distances (q) of less than 30 AU and heliocentric distances outside the orbit of Jupiter, formed by objects entering this region from the Scattered Disk (SD). We perform a numerical integration of 95 real Scattered Disk Objects (SDOs) extracted from the Minor Planet Center database and of 905 synthetic SDOs compensating for observational biases. SDOs have in the Centaur zone a mean lifetime of 72 Myr, though this number falls with a decrease of q. After this incursion, 30% of them enter the zone interior to Jupiter's orbit. We find that the contribution to the Centaur population from the SD gives a total of ∼2.8×108 Centaurs with a radius R>1 km. We also propose a model for the intrinsic distribution of orbital elements of Centaurs and their distance and apparent magnitude distribution.  相似文献   

2.
P. Lamy  I. Toth 《Icarus》2009,201(2):674-713
We present new color results of cometary nuclei obtained with the Hubble Space Telescope (HST) whose superior resolution enables us to accurately isolate the nucleus signals from the surrounding comae. By combining with scrutinized available data obtained with ground-based telescopes, we accumulated a sample of 51 cometary nuclei, 44 ecliptic comets (ECs) and 7 nearly-isotropic comets (NICs) using the nomenclature of Levison [Levison, H.F., 1996. In: Rettig, T.W., Hahn, J.M. (Eds.), Completing the Inventory of the Solar System. In: ASP Conf. Ser., vol. 107, pp. 173-192]. We analyze color distributions and color-color correlations as well as correlations with other physical parameters. We present our compilation of colors of 232 outer Solar System objects—separately considering the different dynamical populations, classical KBOs in low and high-inclination orbits (respectively CKBO-LI and CKBO-HI), resonant KBOs (practically Plutinos), scattered-disk objects (SDOs) and Centaurs—of 12 candidate dead comets, and of 85 Trojans. We perform a systematic analysis of all color distributions, and conclude by synthesizing the implications of the dynamical evolution and of the colors for the origin of the minor bodies of the Solar System. We find that the color distributions are remarkably consistent with the scenarios of the formation of TNOs by Gomes [Gomes, R.S., 2003. Icarus 161, 404-418] generalized by the “Nice” model [Levison, H.F., Morbidelli, A., VanLaerhoven, Ch., Gomes, R., Tsiganis, L., 2008. Icarus 196, 258-273], and of the Trojans by Morbidelli et al. [Morbidelli, A., Levison, H.F., Tsiganis, K., Gomes, R., 2005. Nature 435, 462-465]. The color distributions of the Centaurs are globally similar to those of the CKBO-HI, the Plutinos and the SDOs. However the potential bimodality of their distributions allows to possibly distinguish two groups based on their (B−R) index: Centaur I with (B−R)>1.7 and Centaurs II with (B−R)<1.4. Centaurs I could be composed of TNOs (prominently CKBO-LI) and ultra red objects from a yet unstudied family. Centaurs II could consist in a population of evolved objects which have already visited the inner Solar System, and which has been scattered back beyond Jupiter. The diversity of colors of the ECs, in particular the existence of very red objects, is consistent with an origin in the Kuiper belt. Candidate dead comets represent an ultimate state of evolution as they appear more evolved than the Trojans and Centaurs II.  相似文献   

3.
We study the population of faint Jupiter family comets (JFCs) that approach the Earth (perihelion distances q<1.3 AU) by applying a debiasing technique to the observed sample. We found for the debiased cumulative luminosity function (CLF) of absolute total magnitudes H10 a bimodal distribution in which brighter comets (H10?9) follow a linear relation with a steep slope α=0.65±0.14, while fainter comets follow a much shallower slope α=0.25±0.06 down to H10∼18. The slope can be pushed up to α=0.35±0.09 if a second break in the H10 distribution to a much shallower slope is introduced at H10∼16. We estimate a population of about 103 faint JFCs with q<1.3 AU and 10<H10<15 (radii ∼0.1-0.5 km). The shallowness of the CLF for faint near-Earth JFCs may be explained either as: (i) the source population (the scattered disk) has an equally very shallow distribution in the considered size range, or (ii) the distribution is flattened by the disintegration of small objects before that they have a chance of being observed. The fact that the slope of the magnitude distribution of the faint active JFCs is very similar to that found for a sample of dormant JFCs candidates suggests that for a surviving (i.e., not disintegrated) object, the probability of becoming dormant versus keeping some activity is roughly size independent.  相似文献   

4.
Margaret Pan  Re'em Sari 《Icarus》2005,173(2):342-348
The observed size distribution of Kuiper belt objects (KBOs)—small icy and rocky Solar System bodies orbiting beyond Neptune—is well described by a power law at large KBO sizes. However, recent work by Bernstein et al. (2004, Astron. J. 128, 1364-1390) indicates that the size distribution breaks and becomes shallower for KBOs smaller than about 70 km in size. Here we show that we expect such a break at KBO radius ∼40 km since destructive collisions are frequent for smaller KBOs. Specifically, we assume that KBOs are gravity-dominated bodies with negligible material strength. This gives a power-law slope q?3 where the number N>r of KBOs larger than a size r is given by N>r∝r1−q; the break location follows from this slope through a self-consistent calculation. The existence of this break, the break's location, and the power-law slope we expect below the break are consistent with the findings of Bernstein et al. (2004, Astron. J. 128, 1364-1390). The agreement with observations indicates that KBOs as small as ∼40 km are effectively strengthless.  相似文献   

5.
Though optimized to discover and track fast moving Near-Earth Objects (NEOs), the Near-Earth Asteroid Tracking (NEAT) survey dataset can be mined to obtain information on the comet population observed serendipitously during the asteroid survey. We have completed analysis of over 400 CCD images of comets obtained during the autonomous operations of two 1.2-m telescopes: the first on the summit of Haleakala on the Hawaiian island of Maui and the second on Palomar Mountain in southern California. Photometric calibrations of each frame were derived using background catalog stars and the near-nucleus comet photometry measured. We measured dust production and normalized magnitudes for the coma and nucleus in order to explore cometary activity and comet size-frequency distributions. Our data over an approximately two-year time frame (2001 August-2003 February) include 52 comets: 12 periodic, 19 numbered, and 21 non-periodic, obtained over a wide range of viewing geometries and helio/geocentric distances. Nuclear magnitudes were estimated for a subset of comets observed. We found that for low-activity comets (Afρ<100 cm) our model gave reasonable estimates for nuclear size and magnitude. The slope of the cumulative luminosity function of our sample of low-activity comets was 0.33 ± 0.04, consistent with the slope we measured for the Jupiter-family cometary nuclei collected by Fernández et al. [Fernández, J.A., Tancredi, G., Rickman, H., Licandro, J., 1999. Astron. Astrophys. 392, 327-340] of 0.38 ± 0.02. Our slopes of the cumulative size distribution α=1.50±0.08 agree well with the slopes measured by Whitman et al. [Whitman, K., Morbidelli, A., Jedicke, R., 2006. Icarus 183, 101-114], Meech et al. [Meech, K.J., Hainaut, O.R., Marsden, B.G., 2004. Icarus 170, 463-491], Lowry et al. [Lowry, S.C., Fitzsimmons, A., Collander-Brown, S., 2003. Astron. Astrophys. 397, 329-343], and Weissman and Lowry [Weissman, P.R., Lowry, S.C., 2003. Lunar Planet. Sci. 34. Abstract 34].  相似文献   

6.
The orbital and absolute magnitude distribution of the near-Earth objects (NEOs) is difficult to compute, partly because only a modest fraction of the entire NEO population has been discovered so far, but also because the known NEOs are biased by complicated observational selection effects. To circumvent these problems, we created a model NEO population which was fit to known NEOs discovered or accidentally rediscovered by Spacewatch. Our method was to numerically integrate thousands of test particles from five source regions that we believe provide most NEOs to the inner Solar System. Four of these source regions are in or adjacent to the main asteroid belt, while the fifth one is associated with the transneptunian disk. The nearly isotropic comets, which include the Halley-type comets and the long-period comets, were not included in our model. Test bodies from our source regions that passed into the NEO region (perihelia q<1.3 AU and aphelia Q≥0.983 AU) were tracked until they were eliminated by striking the Sun or a planet or were ejected out of the inner Solar System. These integrations were used to create five residence time probability distributions in semimajor axis, eccentricity, and inclination space (one for each source). These distributions show where NEOs from a given source are statistically most likely to be located. Combining these five residence time probability distributions with an NEO absolute magnitude distribution computed from previous work and a probability function representing the observational biases associated with the Spacewatch NEO survey, we produced an NEO model population that could be fit to 138 NEOs discovered or accidentally rediscovered by Spacewatch. By testing a range of possible source combinations, a best-fit NEO model was computed which (i) provided the debiased orbital and absolute magnitude distributions for the NEO population and (ii) indicated the relative importance of each NEO source region.Our best-fit model is consistent with 960±120 NEOs having H<18 and a<7.4 AU. Approximately 44% (as of December 2000) have been found so far. The limits on this estimate are conditional, since our model does not include nearly isotropic comets. Nearly isotropic comets are generally restricted to a Tisserand parameter (with respect to Jupiter) of T<2, such that few are believed to have a<7.4 AU. Our computed NEO orbital distribution, which is valid for bodies as faint as H<22, indicates that the Amor, Apollo, and Aten populations contain 32±1%, 62±1%, and 6±1% of the NEO population, respectively. We estimate that the population of objects completely inside Earth's orbit (IEOs) arising from our source regions is 2% the size of the NEO population. This value does not include the putative Vulcanoid population located inside Mercury's orbit. Overall, our model predicts that ∼61% of the NEO population comes from the inner main belt (a<2.5 AU), ∼24% comes from the central main belt (2.5<a<2.8 AU), ∼8% comes from the outer main belt (a>2.8 AU), and ∼6% comes from the Jupiter-family comet region (2<T?3). The steady-state population in each NEO source region, as well as the influx rates needed to replenish each region, were calculated as a by-product of our method. The population of extinct comets in the Jupiter-family comet region was also computed.  相似文献   

7.
Short-period comets with P 15 yr represent one of the most complete comet samples. The magnitude distribution of these comets was analysed using a maximum likelihood method. The brightness (magnitude) index for the comets with H 10 11 mag was estimated together with the large sample errors and found to be 0.62 ± 0.09. It was clear that many faint comets with H 10 > 11 mag remain to be discovered. Some of the faint, smaller comets have probably been removed from the distribution altogether.Observational selection was also apparent for the sample of comets with perihelia q < 1.5 AU. It was found that comets satisfying the combined criteria P 15 yr, H 10 11 mag, q < 1.5 AU probably represent the most complete set of comets available. The brightness index of this sample estimated by maximum likelihood was 0.69 ± 0.14. This translates into a mass distribution index s of 1.69 ± 0.14 indicating that most of the mass is contained in a few of the larger comets rather than spread throughout the smaller ones. This distribution, although modified by mass loss, is most likely to have been produced by a process of particle accretion.  相似文献   

8.
We present a new catalog of absolute nuclear magnitudes of Jupiter family (JF) comets, which is an updated version of our previous catalog [Tancredi, G., Fernández, J.A., Rickman, H., Licandro, J., 2000. Astron. Astrophys. Suppl. Ser. 146, 73-90]. From the new catalog we find a linear cumulative luminosity function (CLF) of slope 0.54±0.05 for JF comets with q?2.5 AU. By considering this CLF combined with the few measured geometric albedos with their respective uncertainties, and assuming a canonical albedo of 0.035±0.012 for those comets with undetermined albedos, we derive a cumulative size distribution that follows a power-law of index −2.7±0.3. The slope is similar to that derived from some theoretical collisional models and from some populations of Solar System bodies like the trans-neptunian objects. We also discuss and compare our size distribution with those by other authors that have recently appeared in the literature. Some striking differences in the computed slopes are explained in terms of biases in the studied samples, the different weights given to the brightest members of the samples, and discrepancies in the values of a few absolute nuclear magnitudes. We also compute sizes and fractions of active surface area of JF comets from their estimated absolute nuclear magnitudes and their water production rates. With the outgassing model that we use, about 60% of the computed fractions f of active surface area are found to be smaller than 0.2, with one case (28P/Neujmin 1) of no more than 0.001, which suggests that JF comets may transit through stages of very low activity, or even dormancy. There is an indication that JF comets with radii RN?3 km have active fractions f?0.01, which might be due to the rapid formation of insulating dust mantles on larger nuclei.  相似文献   

9.
The photometric properties of the nucleus of Comet 9P/Tempel 1 are studied from the disk-resolved color images obtained by Deep Impact (DI). Comet Tempel 1 has typical photometric properties for comets and dark asteroids. The disk-integrated spectrum of the nucleus of Tempel 1 between 309 and 950 nm is linear without any features at the spectral resolution of the filtered images. At V-band, the red slope of the nucleus is 12.5±1% per 100 nm at 63° phase angle, translating to B-V=0.84±0.01, V-R=0.50±0.01, and R-I=0.49±0.02. No phase reddening is confirmed. The phase function of the nucleus of Tempel 1 is constructed from DI images and earlier ground-based observations found from the literature. The phase coefficient is determined to be β=0.046±0.007 mag/deg between 4° and 117° phase angle. Hapke's theoretical scattering model was used to model the photometric properties of this comet. Assuming a single Henyey-Greenstein function for the single-particle phase function, the asymmetry factor of Tempel 1 was fitted to be g=−0.49±0.02, and the corresponding single-scattering albedo (SSA) was modeled to be 0.039±0.005 at 550 nm wavelength. The SSA spectrum shows a similar linear slope to that of the disk-integrated spectrum. The roughness parameter is found to be 16°±8°, and independent of wavelength. The Minnaert k parameter is modeled to be 0.680±0.014. The photometric variations on Tempel 1 are relatively small compared to other comets and asteroids, with a ∼20% full width at half maximum of albedo variation histogram, and ∼3% for color. Roughness variations are evident in one small area, with a roughness parameter about twice the average and appearing to correlate with the complex morphological texture seen in high-resolution images.  相似文献   

10.
Two indices have been developed for the purpose of comparing the natures of various classes of comets. The first is the Activity Index (AI), measuring the inherent magnitude increase in brightness from great solar distances to maximum near perihelion. The second, or Volatility Index (VI), measures the variation in magnitude near perihelion. Tentative determinations of these two indices are derived from observations by Max Beyer over more than 30 years for long-period (L-P) and short-period (S-P) comets near perihelion and from other homogeneous sources. AI determinations are made for 32 long-period (L-P) comets and for 14 short-period (S-P). The range of values of AI is of the order of 3 to 10 magnitudes with a median about 6. An expected strong correlation with perihelion distance q, is found to vary as q –2.3. Residuals from a least-square solution (AI) are used for comparing comets of different orbital classes, the standard deviation of a single value of AI is only ±1m.1 for L-P comets and ±1m.2 for S-P comets.Among the L-P comets, 19 of period P larger than 104 years yield AI = 0m.27 ± 0m.25 compared to 0m.39 ± 0m.26 for 13 of period between 102 years and 104 years. This denies any fading with aging among the L-P comets. Also no systematic change with period occurs for the VI index, leading to the same conclusions. Weak correlations are found with the Gas/Dust ratio of comets. No correlations are found between the two indices, nor of either index with near-perihelion magnitudes or orbital inclination.The various data are consistent with a uniform origin for all types of comets, the nuclei being homogeneous on the large scale but quite diverse on a small scale (the order of a fraction of kilometer in extent). Small comets thus may sublimate away entirely, leaving no solid core, while huge comets may develop a less volatile core by radioactive heating and possibly become inactive like asteroids after many S-P revolutions about the Sun. When relatively new, huge comets may be quite active at great solar distances because of volatiles from the core that have refrozen in the outer layers.  相似文献   

11.
A numerical simulation of the Oort cloud is used to explain the observed orbital distributions and numbers of Jupiter-family (JF) and Halley-type (HT) short-period (SP) comets. Comets are given initial orbits with perihelion distances between 5 and 36 au, and evolve under planetary, stellar and Galactic perturbations for 4.5 Gyr. This process leads to the formation of an Oort cloud (which we define as the region of semimajor axes a > 1,000 au), and to a flux of cometary bodies from the Oort cloud returning to the planetary region at the present epoch. The results are consistent with the dynamical characteristics of SP comets and other observed cometary populations: the near-parabolic flux, Centaurs, and high-eccentricity trans-Neptunian objects. To achieve this consistency with observations, the model requires that the number of comets versus initial perihelion distance is concentrated towards the outer planetary region. Moreover, the mean physical lifetime of observable comets in the inner planetary region (q < 2.5 au) at the present epoch should be an increasing function of the comets’ initial perihelion distances. Virtually all observed HT comets and nearly half of observed JF comets come from the Oort cloud, and initially (4.5 Gyr ago) from orbits concentrated near the outer planetary region. Comets that have been in the Oort cloud also return to the Centaur (5 < q < 28 au, a < 1,000 au) and near-Neptune high-eccentricity regions. Such objects with perihelia near Neptune are hard to discover, but Centaurs with characteristics predicted by the model (e.g. large semimajor axes, above 60 au, or high inclinations, above 40°) are increasingly being found by observers. The model provides a unified picture for the origin of JF and HT comets. It predicts that the mean physical lifetime of all comets in the region q < 1.5 au is less than ～200 revolutions.  相似文献   

12.
Possibilities to explain the observed 1/a-distribution are discussed in the light of improved understanding of the dynamical evolution of long-period comets. It appears that the ‘fading problem’ applies both to single-injection and continuous-injection models. Although uncertainties due to nongravitational effects do not allow detailed results to be drawn from the observed 1/a-distribution at small perihelion distance q, that for q ? 1.5 AU shows that a constant fading probability cannot explain all the features of the observed distribution. Assuming that comets can reappear following a period of fading, values for the assumed constant fading and renewal probabilities, and the total cometary flux have been estimated for q > 1.5 AU.  相似文献   

13.
Six nights of R-band CCD observations of the classical Kuiper Belt Object (KBO) 20000 Varuna (2000 WR106) were obtained at the Palomar Mountain 60- and 200-in telescopes. The observations were scheduled to take advantage of a particularly favorable apparition which allowed us to sample down to extremely small solar phase angle (α=0.036°). After rotational lightcurve subtraction, we found that the KBO exhibited a strong opposition surge of ∼0.1 mag at phase angles α<0.1°. We modeled our composite solar phase curve of Varuna using both H-G parameterization and Hapke theory and concluded that similar opposition surges may be wide spread among KBOs and that the regolith of Varuna may be significantly more porous than a typical main-belt C-type asteroid. Wide-spread opposition surges lead to higher albedos than derived assuming linear phase behavior: on the whole KBOs may be brighter than previously assumed.  相似文献   

14.
We present the characteristics of the dust comae of two comets, 126P/IRAS, a member of the Halley family (a near-isotropic comet), and 2P/Encke, an ecliptic comet. We have primarily used mid- and far-infrared data obtained by the ISOPHOT instrument aboard the Infrared Space Observatory (ISO) in 1996 and 1997, and mid-infrared data obtained by the SPIRIT III instrument aboard the Midcourse Space Experiment (MSX) in 1996. We find that the dust grains emitted by the two comets have markedly different thermal and physical properties. P/IRAS's dust grain size distribution appears to be similar to that of fellow family member 1P/Halley, with grains smaller than 5 microns dominating by surface area, whereas P/Encke emits a much higher fraction of big (20 μm and higher) grains, with the grain mass distribution being similar to that which is inferred for the interplanetary dust population. P/Encke's dearth of micron-scale grains accounts for its visible-wavelength classification as a “gassy” comet. These conclusions are based on analyses of both imaging and spectrophotometry of the two comets; this combination provides a powerful way to constrain cometary dust properties. Specifically, P/IRAS was observed preperihelion while 1.71 AU from the Sun, and seen to have a 15-arcmin long mid-infrared dust tail pointing in the antisolar direction. No sunward spike was seen despite the vantage point being nearly in the comet's orbital plane. The tail's total mass at the time was about 8×109 kg. The spectral energy distribution (SED) is best fit by a modified greybody with temperature T=265±15 K and emissivity ε proportional to a steep power law in wavelength λ: ε∝λ−α, where α=0.50±0.20(2σ). This temperature is elevated with respect to the expected equilibrium temperature for this heliocentric distance. The dust mass loss rate was between 150-600 kg/s (95% confidence), the dust-to-gas mass loss ratio was about 3.3, and the albedo of the dust was 0.15±0.03. Carbonaceous material is depleted in the comet's dust by a factor of 2-3, paralleling the C2 depletion in P/IRAS's gas coma. P/Encke, on the other hand, observed while 1.17 AU from the Sun, had an SED that is best fit by a Planck function with T=270±15 K and no emissivity falloff. The dust mass loss rate was 70-280 kg/s (95% confidence), the dust-to-gas mass loss ratio was about 2.3, and the albedo of the dust was about 0.06±0.02. These conclusions are consistent with the strongly curved dust tail and bright dust trail seen by Reach et al. (2000; Icarus 148, 80) in their ISO 12-μm imaging of P/Encke. The observed differences in the P/IRAS and P/Encke dust are most likely due to the less evolved and insolated state of the P/IRAS nuclear surface. If the dust emission behavior of P/Encke is typical of other ecliptic comets, then comets are the major supplier of the interplanetary dust cloud.  相似文献   

15.
The Wide Field Camera (WFC) on the Hubble Space Telescope and the Low Resolution Imaging Spectrograph (LRIS) on the Keck II telescope have been used to image 21 distant dynamically new, long-period (LP) and short-period (SP) Jupiter-family (JF) comet nuclei (near aphelion), as part of a long-term program to search for physical differences between short-period comets and Oort cloud comets. WFC data were obtained on Comets C/1987 H1 (Shoemaker) and C/1984 K1 (Shoemaker) during Cycle 5 (1995 December) and on C/1988 B1 (Shoemaker), C/1987 F1 (Torres), and C/1983 O1 (?ernis) during Cycle 6 (1997 April, May, and June). The HST comets were at heliocentric distances 20.4 < r[AU] < 29.5. Each comet observation was allocated 7 orbits, for ≈3.6 hrs of integration. The most difficult part of the image reduction was the removal of cosmic rays. We present our scheme for cosmic ray removal. None of the HST comet nuclei was detected to the 3-σ level at mR∼27. The inferred upper limits to the nucleus radii are . The SP comets range in radius between , with a median value of RN∼1.61 km. The LP comets ranged in size between <4.0-56 km. Over a range of radii between 1-10 km, the nuclei can be fit with a cumulative distribution N(>RN)∝RN−α with α=1.45±0.05, and for nuclei in the range 2-5 km, α=1.91±0.06. Statistical analysis and modeling shows that the slopes of the observed TNO and JF comet distributions are not compatible, suggesting that the intrinsic distribution of JF comet nuclei is a differential a−3.5 power law truncated at small nucleus radii between 0.3 and 2.0 km.  相似文献   

16.
We analyze the dynamical evolution of Jupiter-family (JF) comets and near-Earth asteroids (NEAs) with aphelion distances Q>3.5 AU, paying special attention to the problem of mixing of both populations, such that inactive comets may be disguised as NEAs. From numerical integrations for 2×106 years we find that the half lifetime (where the lifetime is defined against hyperbolic ejection or collision with the Sun or the planets) of near-Earth JF comets (perihelion distances q<1.3 AU) is about 1.5×105 years but that they spend only a small fraction of this time (∼ a few 103 years) with q<1.3 AU. From numerical integrations for 5×106 years we find that the half lifetime of NEAs in “cometary” orbits (defined as those with aphelion distances Q>4.5 AU, i.e., that approach or cross Jupiter's orbit) is 4.2×105 years, i.e., about three times longer than that for near-Earth JF comets. We also analyze the problem of decoupling JF comets from Jupiter to produce Encke-type comets. To this end we simulate the dynamical evolution of the sample of observed JF comets with the inclusion of nongravitational forces. While decoupling occurs very seldom when a purely gravitational motion is considered, the action of nongravitational forces (as strong as or greater than those acting on Encke) can produce a few Enckes. Furthermore, a few JF comets are transferred to low-eccentricity orbits entirely within the main asteroid belt (Q<4 AU and q>2 AU). The population of NEAs in cometary orbits is found to be adequately replenished with NEAs of smaller Q's diffusing outward, from which we can set an upper limit of ∼20% for the putative component of deactivated JF comets needed to maintain such a population in steady state. From this analysis, the upper limit for the average time that a JF comet in near-Earth orbit can spend as a dormant, asteroid-looking body can be estimated to be about 40% of the time spent as an active comet. More likely, JF comets in near-Earth orbits will disintegrate once (or shortly after) they end their active phases.  相似文献   

17.
Using the N-body dynamical model that includes the sun, the 8 planets, Pluto, UB313 and massless particles, we simulate the orbital evolution of 551 Kuiper Belt Objects (KBOs) with known parameters. The initial conditions of the simulations are the currently observed orbital parameters. The integration backtracks from now to -10×108 yr. The results show that about 10×108 years ago, more than 1/3 of the presently observed KBOs resided in the region of the present Kuiper main belt, a few were located inside the Neptune orbit, and the rest were beyond 50AU; and that about 4.5×108 years ago, all the objects in the Kuiper main belt exhibited a rather good normal distribution, without so many objects concentrated in the Neptune's 3:2 resonance region, as at present time.  相似文献   

18.
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.  相似文献   

19.
Y.J. Choi  N. Brosch 《Icarus》2003,165(1):101-111
We describe observations of the scattered Kuiper Belt object (29981) 1999 TD10 performed during five observing runs at two observatories, over 370 days from 2000 September to 2001 September. They show significant brightness variations that fit a double-peaked lightcurve with period 15.448±0.012 h in V and R bands. The phase effect in V band, 0.09±0.01 mag deg−1, is smaller than that of Pluto but larger than that of several KBOs, while in R band it is 0.030±0.005 mag deg−1. We find color variation between the two bands, which implies a non-homogeneous albedo distribution on the surface. Evidence of surface activity near perihelion in the form of a coma/tail is presented using radial image profiles and a 2D contour map.  相似文献   

20.
This study analyzes the evolution of 2 × 105 orbits with initial parameters corresponding to the orbits of comets of the Oort cloud under the action of planetary, galactic, and stellar perturbations over 2 × 109 years. The dynamical evolution of comets of the outer (orbital semimajor axes a > 104 AU) and inner (5 × 103 < a (AU) < 104) parts of the comet cloud is analyzed separately. The estimates of the flux of “new” and long-period comets for all perihelion distances q in the planetary region are reported. The flux of comets with a > 104 AU in the interval 15 AU < q < 31 AU is several times higher than the flux of comets in the region q < 15 AU. We point out the increased concentration of the perihelia of orbits of comets from the outer cloud, which have passed several times through the planetary system, in the Saturn-Uranus region. The maxima in the distribution of the perihelia of the orbits of comets of the inner Oort cloud are located in the Uranus-Neptune region. “New” comets moving in orbits with a < 2 × 104 AU and arriving at the outside of the planetary system (q > 25 AU) subsequently have a greater number of returns to the region q < 35 AU. The perihelia of the orbits of these comets gradually drift toward the interior of the Solar System and accumulate beyond the orbit of Saturn. The distribution of the perihelia of long-period comets beyond the orbit of Saturn exhibits a peak. We discuss the problem of replenishing the outer Oort cloud by comets from the inner part and their subsequent dynamical evolution. The annual rate of passages of comets of the inner cloud, which replenish the outer cloud, in the region q < 1 AU in orbits with a > 104 AU (～ 5.0 × 10?14 yr?1) is one order of magnitude lower than the rate of passage of comets from the outer Oort cloud (～ 9.1 × 10?13 yr?1).  相似文献   

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