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1.
Comet C/2001 A2 experienced several splitting events duringits 2001 perihelion passage. The first break-upevent was observed in March 2001 (IAUC 7616).In this paper we report the first results of ourextensive imaging and spectroscopic monitoring campaignwith ESO telescopes over several weeks before andafter the perihelion passage on May 25 2001.  相似文献   

2.
We present observations of the extended dust structures near the orbits of three short-period comets: 2P/Encke, 22P/Kopff, and 65P/Gunn. The dust trails were originally discovered by the Infrared Astronomical Satellite (IRAS). Our observations were made using wide-field optical CCD cameras on the University of Hawaii 2.24-m telescope, the Canada-France-Hawaii 3.6-m telescope, and the Kiso 1.05-m Schmidt telescope. We compared the observed images with models and found that the extended structures seen around 2P/Encke and 22P/Kopff before perihelion passage were most likely “dust trails,” whereas images taken after perihelion passage show a high contamination by recently released particles (i.e., particles in Neck-Line structures are visible). We could not confirm the existence of a dust trail from 65P/Gunn within the field of view of the camera used. The effective sizes of the particles responsible for the scattered light were estimated at 1-100 mm (2P/Encke), 1-10 mm (22P/Kopff), and 100 μm-1 mm (65P/Gunn), respectively, which is consistent with previous studies of dust trails made with infrared space telescopes and optical telescopes. We evaluated the mass loss rates of these comets, averaged over their orbits, as reaching (2P/Encke), (22P/Kopff), and (65P/Gunn). These values are consistent with previous work. Therefore, the total amount of material ejected from these three comets is , which would contribute a considerable fraction of the lost within 1 AU that needs to be replaced if the zodiacal cloud is to be maintained in a steady state. We also found that the particles in the dust structures are significantly redder than the Sun and the zodiacal light, and might be redder than the average short-period comet nuclei. Specifically, the reflectivity gradients of 2P/Encke, 22P/Kopff, and 65P/Gunn are 13±7 (% 103 Å−1), 20±5 (% 103 Å−1), and 15±4 (% 103 Å−1), respectively. We examined the change in color with distance from the nucleus. No clear correlation was detected for 2P/Encke or 22P/Kopff to an accuracy of 3-11%, while the 65P/Gunn tail did show color variation, becoming redder with increasing distance from the nucleus. This dark red material, consisting of particles of sand-cobble size, has marginally escaped from the nuclei and will evolve into finer-grained interplanetary dust particles after subsequent collisions.  相似文献   

3.
Near-simultaneous R- and J-band photometric measurements of the short-period Comets 2P/Encke and the Deep Impact mission target 9P/Tempel 1 were obtained. The resulting R-J colors are +0.82±0.08 mag and +1.46±0.13 mag for Encke and Tempel 1, respectively. Tempel 1's color is redder than the solar R-J color index of +0.76. The Tempel 1 observations directly detected the nucleus while the Encke observations likely suffered from coma contamination.  相似文献   

4.
On the origin of the unusual orbit of Comet 2P/Encke   总被引：1，自引：0，他引：1  
The orbit of Comet 2P/Encke is difficult to understand because it is decoupled from Jupiter—its aphelion distance is only 4.1 AU. We present a series of orbital integrations designed to determine whether the orbit of Comet 2P/Encke can simply be the result of gravitational interactions between Jupiter-family comets and the terrestrial planets. To accomplish this, we integrated the orbits of a large number of objects from the trans-neptunian region, through the realm of the giant planets, and into the inner Solar System. We find that at any one time, our model predicts that there should be roughly 12 objects in Encke-like orbits. However, it takes roughly 200 times longer to evolve onto an orbit like this than the typical cometary physical lifetime. Thus, we suggest that (i) 2P/Encke became dormant soon after it was kicked inward by Jupiter, (ii) it spent a significant amount of time inactive while rattling around the inner Solar System, and (iii) it only became active again as the ν6 secular resonance drove down its perihelion distance.  相似文献   

5.
Photoelectric observations of Comet P/Encke during its 1980 apparition are combined with other published data to relate molecular production rates to the visual lightcurve. In addition to a substantial asymmetry about perihelion which is already well known, there are shorter-term variations in specific molecules which have not been duplicated by models. The most dramatic of these fluctuations is a rapid decrease by more than a factor of 3 in the production of OH at 0.75 AU preperihelion.  相似文献   

6.
We analyzed the visible broadband photometric data of comets 1P/Halley and 4P/Faye, obtained during their perihelion passages of 1986 and 1991, respectively at the Sanglokh Observatory (Tajikistan) and the European Southern Observatory (Chile). Applying the Lomb-Scargle periodogram in the V-band magnitudes and B-V color index, we find that the most probable periodicities are 79 ± 6 and 7.36 ± 0.04 days for 1P, and 6.1 ± 0.3 days for 4P. After comparing results of color and magnitude periodograms, we argue there is a systematic difference in the number of signals identified and the level of confidence of the same periodicity in the periodograms. Our results suggest the quest for periodicities in the color of the coma of active comets should be complementary to ones in magnitudes. We have verified that the distribution of the color B-V of Faye’s coma was invariable during and after the possible occurrence of a post-perihelion outburst. We verify a symmetry in the pre- and post-perihelion H0 photoelectric absolute magnitude of the comet Halley. The same issues were not observed in the B-V color index. We verify that the absolute magnitude H0 of the comet Halley differs from each other when calculated from the visual or photoelectric magnitudes, due to the section of the coma used to estimate these magnitudes. We also verified that this difference in the photometric aperture can compromise comparisons of B-V color distributions between active comets.  相似文献   

7.
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   

8.
A supposition about the common origin of some cometary and asteroidal members of the Taurid complex is analyzed on the basis of their orbital evolution. It is shown that moments, in which the longitudes of perihelion of comet P/Encke, object (2201) Oljato and six other near-Earth asteroids amount to the value of longitude of perihelion of comet 1967 II Rudnicki, are close to the moment of previous perihelion passage of this long-period comet. Although the conjecture about the membership of comet Rudnicki in the Taurid complex is controversial one, nevertheless the presented results seem to be interesting in itself, and yield a contribution in favour of the hypothesis of the breakup of a giant comet some 104 – 105 years ago in the inner Solar System.  相似文献   

9.
Comet C/2009 P1 (Garradd) was observed by imaging polarimetry for nearly 5 months from October 2011 to March 2012, over an intermediate phase angle range (28°–35°). Two months before perihelion and one month after, dust particles seem to be ejected all around the optocenter and jets extend to distances greater than 40,000 km. An increase of activity is noticed in intensity and polarization after perihelion. Two months before perihelion and one month after, the dust emission seems to be all around the optocenter. Two and three months after perihelion the jets are mainly toward the solar direction with an extension of more than 20,000 km projected on the sky. The values of the aperture polarization are comparable to those of other comets. On the polarization maps in October 2011 and January 2012 the higher polarization zones extend in large regions perpendicularly to the solar direction where jets are also observed. In February and March 2012, the polarization in the jets is larger in the solar direction than in the surrounding coma. By its activity visible on intensity images and polarization maps at large distances from the nucleus, comet Garradd probably belongs to the high‐Pmax class of comets.  相似文献   

10.
Comet 81P/Wild 2 was observed in the thermal infrared over 6 months during its 1997 perihelion passage. The comet was most active in late February, about 3 months preperihelion; dust production declined by a factor of 3 between February and August. For the GIOTTO Halley dust size distribution, maximum dust production rate was ∼2 × 106 g/s. The comet displayed a 10-μm silicate feature about 25% above the continuum, similar to several other Jupiter-family comets, but much lower than that seen in a number of Oort cloud comets.NASA’s STARDUST sample return mission will encounter P/Wild 2 98 days postperihelion in January 2004. Based on our observations at a similar point in the orbit and the Halley size distribution, we predict that the mass fluence on the spacecraft for a 150 km miss distance will be about 8 × 10−6 g/cm2 for particles up to 1 cm in radius. The corresponding areal coverage will be about 10−4.  相似文献   

11.
The shape and intensity distribution of tails for several large comets are estimated on the basis of grain properties in the solar radiation field. The following results are obtained: (1) The ratio of the maximum radiation pressure force to the gravitaional force acting on dust grains in cometary tails is found to be less than 2.5. This means that grains such as graphite particles in the size range 0.02–0.2 μm do not exist in them, because such particles would allow forces greater than 2.5 (2) Tail substances supplied near the time of perihelion passage for the Sun-grazing comet Ikeya-Seki (1965 VIII) and Comet Seki-Lines (1962 III) were composed of particular grains which had values of radiation pressure ratio less than 1.0. Therefore, it is concluded that the material was composed of silicate grains only, since iron grains had sublimated and there were no graphite particles.  相似文献   

12.
We present the study of dust environment of dynamically new Comet C/2003 WT42 (LINEAR) based on spectroscopic and photometric observations. The comet was observed before and after the perihelion passage at heliocentric distances from 5.2 to 9.5 AU. Although the comet moved beyond the zone where water ice sublimation could be significant, its bright coma and extended dust tail evidenced the high level of physical activity. Afρ values exceeded 3000 cm likely reaching its maximum before the perihelion passage. At the same time, the spectrum of the comet did not reveal molecular emission features above the reflected continuum. Reddening of the continuum derived from the cometary spectrum is nonlinear along the dispersion with the steeper slop in the blue region. The pair of the blue and red continuum images was analyzed to estimate a color of the comet. The mean normalized reflectivity gradient derived from the innermost part of the cometary coma equals to 8% per 1000 Å that is typical for Oort cloud objects. However, the color map shows that the reddening of the cometary dust varies over the coma increasing to 15% per 1000 Å along the tail axis. The photometric images were fitted with a Monte Carlo model to construct the theoretical brightness distribution of the cometary coma and tail and to investigate the development of the cometary activity along the orbit. As the dust particles of distant comets are expected to be icy, we propose here the model, which describes the tail formation taking into account sublimation of grains along their orbits. The chemical composition and structure of these particles are assumed to correspond with Greenberg’s interstellar dust model of comet dust. All images were fitted with the close values of the model parameters. According to the results of the modeling, the physical activity of the comet is mainly determined by two active areas with outflows into the wide cones. The obliquity of the rotation axis of the nucleus equals to 20° relative to the comet’s orbital plane. The grains occupying the coma and tail are rather large amounting to 1 mm in size, with the exponential size distribution of a−4.5. The outflow velocities of the dust particles vary from a few centimeters to tens of meters per second depending on their sizes. Our observations and the model findings evidence that the activity of the nucleus decreased sharply to a low-level phase at the end of April–beginning of May 2007. About 190 days later, in the first half of November 2007 the nucleus stopped any activity, however, the remnant tail did not disappear for more than 1.5 years at least.  相似文献   

13.
We interpret the historical activity of comet 55P/Tempel–Tuttle in terms of the observed characteristics of present-day short period comets. In this respect, it is now realized that such comets are liable to undergo significant outburst and mantle loss events at intervals separated by of order a few hundred years. On this basis one might well expect comet 55P/Tempel–Tuttle to have undergone several outbursts since its earliest sighing in 1366. The limited absolute magnitude data available for 55P/Tempel–Tuttle is not inconsistent with the suggestion that the comet underwent outbursts during its 1699 and 1865 perihelion returns. If the outbursts of comet 55P/Tempel–Tuttle are interpreted in terms of mantle loss events then the bright, electrophonic sound producing fireballs reported during the great Leonid meteor storm of 1833 may have been due to the Earth sampling mantle material ejected during the outburst of 1699. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

14.
Hanner  M. S.  Gehrz  R. D.  Harker  D. E.  Hayward  T. L.  Lynch  D. K.  Mason  C. C.  Russell  R. W.  Williams  D. M.  Wooden  D. H.  Woodward  C. E. 《Earth, Moon, and Planets》1997,79(1-3):247-264
The dust coma of comet Hale-Bopp was observed in the thermal infrared over a wide range in solar heating (R = 4.9–0.9 AU) and over the full wavelength range from 3 μm to 160 μm. Unusual early activity produced an extensive coma containing small warm refractory grains; already at 4.9 AU, the 10 μm silicate emission feature was strong and the color temperature was 30% above the equilibrium blackbody temperature. Near perihelion the high color temperature, strong silicate feature, and high albedo indicated a smaller mean grain size than in other comets. The 8–13 μm spectra revealed a silicate emission feature similar in shape to that seen in P/Halley and several new and long period comets. Detailed spectral structure in the feature was consistent over time and with different instruments; the main peaks occur at 9.3, 10.0 and 11.2 μm. These peaks can be identified with olivine and pyroxene minerals, linking the comet dust to the anhydrous chondritic aggregate interplanetary dust particles. Spectra at 16–40 μm taken with the ISO SWS displayed pronounced emission peaks due to Mg-rich crystalline olivine, consistent with the 11.2 μm peak. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

15.
We report the detection of the nucleus of Comet 22P/Kopff with the Planetary Camera of the Hubble Space Telescope (HST) and with the Infrared Camera of the Infrared Space Observatory (ISOCAM). The HST observations were performed on 18 July 1996, 16 days after its perihelion passage of 2 July 1996, when it was at Rh=1.59 AU from the Sun and Δ=0.57 AU from the Earth. A sequence of images taken with four broad-band filters was repeated eight times over a 12-h time interval. The ISOCAM observations were performed on 15 October 1996, 106 days after the perihelion passage, when the comet was at Rh=1.89 AU from the Sun and Δ=1.32 AU from the Earth. Seven images were obtained with a broad-band filter centered at 11.5 μm. In both instances, the spatial resolution was appropriate to separate the signal of the nucleus from that of the coma. We determine the Johnson-Kron-Cousins BVRI magnitudes of the nucleus. The visible lightcurves constrain neither the rotation period nor the ratio of semiaxes. We favor the solution of a rather spherical nucleus, although the situation of a pole-on view of an irregular body cannot be excluded. The systematic decreasing trend of the lightcurves could suggest a period of several days. Combining the visible and infrared observations, we find that an ice-dust mixed model is ruled out, while the standard thermal model leads to a nuclear radius of Rn=1.67±0.18 km of albedo pv=0.042±0.006. The red color of the nucleus is characterized by a nearly constant gradient of S′=14±5% per kÅ from 400 to 800 nm. We estimate a fractional active area of 0.35 which places 22P/Kopff in the class of highly active short-period comets. At Rh=1.59 AU, the dust coma is characterized by a red color with a reflectivity gradient S′=17±3% per kÅ, compatible with that of the nucleus, and Afρ=545 cm, yielding a dust production rate of Qd=130 kg sec−1.  相似文献   

16.
Masateru Ishiguro 《Icarus》2008,193(1):96-104
A thin, bright dust cloud, which is associated with the Rosetta mission target object (67P/Churyumov-Gerasimenko), was observed after the 2002 perihelion passage. The neckline structure or dust trail nature of this cloud is controversial. In this paper, we definitively identify the dust trail and the neckline structure using a wide-field CCD camera attached to the Kiso 1.05-m Schmidt telescope. The dust trail of 67P/Churyumov-Gerasimenko was evident as scattered sunlight in all images taken between September 9, 2002 and February 1, 2003, whereas the neckline structure became obvious only after late 2002. We compared our images with a semi-analytical dynamic model of dust grains emitted from the nucleus. A fading of the surface brightness of the dust trail near the nucleus enabled us to determine the typical maximum size of the grains. Assuming spherical compact particles with a mass density of 103 kg m−3 and an albedo of 0.04, we deduced that the maximum diameter of the dust particles was approximately 1 cm. We found that the mass-loss rate of the comet at the perihelion was on or before the 1996 apparition, while the mass-loss rate averaged over the orbit reached . The result is consistent with the studies of the dust cloud emitted in the 2002/2003 return. Therefore, we can infer that the activity of 67P/Churyumov-Gerasimenko has showed no major change over the past dozen years or so, and the largest grains are cyclically injected into the dust tube lying along the cometary orbit.  相似文献   

17.
The comet 67P/Churyumov-Gerasimenko is the current target of the mission Rosetta, initially planned to investigate comet 46P/Wirtanen. These two comets have similar orbits, except the distance to the Sun at perihelion, but different orbital histories and different masses. Thus, structures of the nuclei can be significantly different. The evolution of comet Wirtanen was simulated by several authors, while comet Churyumov-Gerasimenko became an object of high interest only recently and is not well investigated. In the present work we simulate the evolution of the nucleus, down to tens of meters below the surface, using an extended version of the model previously applied for comet Wirtanen [Kossacki et al., 1999. Comet 46P/Wirtanen: evolution of the subsurface layer. Icarus 142, 202-218.]. The model includes strengthening of the nucleus due to sintering of the ice grains. Simulations are performed for different latitudes, accounting for the evolution of the orbit and for changes of the nucleus orientation, as well as diurnal and seasonal changes of insolation. The calculated loss of water vapor from the comet is integrated over the nucleus surface and is compared with the observational data. We have found, that the sublimation through the dust mantle can be large enough to reproduce the profile of the total water production as a function of time from perihelion. The required dependence of thickness of the dust layer on latitude qualitatively matches present distribution of the absorbed solar flux. The non-gravitational acceleration in the comet motion together with the simulated sublimation flux are used in order to estimate the mass and the bulk density of the nucleus.  相似文献   

18.
Based on the number of planet-approaching cometary orbits at Mars and Venus relative to the Earth, there should be ample opportunities for observing meteor activity at those two planets. The ratio of planet-approaching Jupiter family comets (JFCs) at Mars, Earth, and Venus is 4:2:1 indicating that JFC-related outbursts would be more frequent at Mars than the Earth. The relative numbers of planet-approaching Halley-type comets (HTCs) implies that the respective levels of annual meteor activity at those three planets are similar. We identify several instances where near-comet outbursts (Jenniskens, P.: 1995, Astron. Astrophys. 295, 206–235) may occur. A possible double outburst of this type at Venus related to 45P/Honda-Mrkos-Padjusakova may be observable by the ESA Venus Express spacecraft in the summer of 2006. Similarly, the Japanese Planet-C Venus orbiter may observe an outburst related to 27P/Crommelin’s perihelion passage in July 2011. Several additional opportunities exist to observe such outbursts at Mars from 2019 to 2026 associated with comets 38P/Stephan-Oterma, 13P/Olbers and 114P/Wiseman-Skiff.  相似文献   

19.
《Planetary and Space Science》1999,47(6-7):725-733
The SWAN instrument on board SOHO is a Lyman-α photometer able to map the sky intensity with a resolution of 1°, primarily devoted to the study of the large scale distribution of solar wind from its imprints on the interplanetary sky background. In addition SWAN was extensively used to map the Lyman α emission of several comets since launch in December 1995. Here we report observations of Comet 46 P/Wirtanen near perihelion. From the recorded Lyman α intensity the H2O production rate was derived for 45 observations from 21 December 1996–17 May 1997, with a peak of 1.6±0.4×1028 mol/s just before perihelion. This should help to constrain the physical models of 46 P/Wirtanen for Rosetta mission planning purposes.  相似文献   

20.
Comet 1996 B2 (Hyakutake) displayed strong evidence for break-up, with a prominent antisunward dust spike and fragments traveling antisunward for many days after an eruptive event in late March 1996. Because of its high orbital inclination and rapid southward motion after perihelion, its post-perihelion activity was not well monitored from the ground. The SWAN all-sky Lyman-alpha camera on the SOHO spacecraft was ideally placed for long-term monitoring of the hydrogen coma of Comet Hyakutake both before and after perihelion. The SWAN images were analyzed with a new time-resolved model (TRM) that provides daily averages of the water production rate and an estimate of the hydrogen atom lifetime (dominated by charge exchange with solar wind protons) during extended periods throughout the apparition. A long-term variation of water production rate of , where r is the heliocentric distance in AU was found. The daily average values of the production rate covered the March 19 outburst and two more outbursts seen in the April before perihelion, which had progressively shorter durations at respectively smaller heliocentric distances. The long-term variation of the production rate was found to be consistent with the seasonal effect predicted by the jet rotation model of Schleicher and Woodney [2003. Analyses of dust coma morphology of Comet Hyakutake (1996 B2) near perigee: Outburst behavior, jet motion, source region locations, and the nucleus pole orientation. Icarus 162, 190-213] when added to a more steady source that is about two-thirds of the maximum of the jet source. The seasonal effect in their model found the dust jet source largely not illuminated after perihelion, coinciding with somewhat reduced overall activity and the absence of outbursts and fragmentation. The locations of the dust jets appear to be responsible for the outbursts and fragmentation before perihelion. The erratic behavior of the pre-perihelion jet sources as contrasted with the smoother variation from the rest of the surface after perihelion indicates there is a strong heterogeneity in the physical make-up of active areas on the nucleus.  相似文献   

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