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1.
The meteoroid streams associated to short-period comets 9P/Tempel 1 (the target of the Deep Impact mission). and 67P/Churyumov-Gerasimenko (the target of the Rosetta mission) are studied. Their structure is overwhelmingly under the
control of Jupiter and repeated relatively close encounters cause a reversal of the direction of the spatial distribution
of the stream relative to the comet* an initial stream trailing the comet as usually seen eventually collapses, becomes a
new stream leading the comet and even splits into several components. Although these two comets do not produce meteor showers
on Earth, this above feature shows that meteor storms can occur several years before the perihelion passage of a parent body. 相似文献
2.
Jozef Klačka 《Earth, Moon, and Planets》1994,65(2):191-196
The action of the solar electromagnetic radiation on the moving interplanetary dust particles in its more complete form than the special case known as the Poynting-Robertson effect is theoretically discussed in application to meteoroid stream of comet Encke.Normal and transversal components of the perturbing nongravitational force are used due to the action of the solar electromagnetic radiation. It is shown that the normal component of the force is negligible. However, transversal component is very important: it can probably completely explain all the observed meteoroid streams situated along the orbit of comet Encke (and, possibly, some asteroids) as the product of the comet Encke alone. Much shorter time is required for producing such a meteoroid stream than is a general conception.If the idea about the significance of the transversal component of the nongravitational force (may be, not produced by electromagnetic radiation) is correct, it may have important consequences for our understanding of ageing of comets, global evolution of the cometary (and, partially, asteroidal) system, and, of course, for a long-term evolution of small interplanetary particles. 相似文献
3.
We deal with theoretical meteoroid streams the parent bodies of which are two Halley-type comets in orbits situated at a relatively
large distance from the orbit of Earth: 126P/1996 P1 and 161P/2004 V2. For two perihelion passages of each comet in the far
past, we model the theoretical stream and follow its dynamical evolution until the present. We predict the characteristics
of potential meteor showers according to the dynamical properties of theoretical particles currently approaching the orbit
of the Earth. Our dynamical study reveals that the comet 161P/2004 V2 could have an associated Earth-observable meteor shower,
although no significant number of theoretical particles are identified with real, photographic, video, or radar meteors. However,
the mean radiant of the shower is predicted on the southern sky (its declination is about −23°) where a relatively low number
of real meteors has been detected and, therefore, recorded in the databases used. The shower of 161P has a compact radiant
area and a relatively large geocentric velocity of ∼53 km s−1. A significant fraction of particles assumed to be released from comet 126P also cross the Earth’s orbit and, eventually,
could be observed as meteors. However, their radiant area is largely dispersed (declination of radiants spans from about +60°
to the south pole) and, therefore, mixed with the sporadic meteor background. An identification with real meteors is practically
impossible. 相似文献
4.
Peter Jenniskens 《Earth, Moon, and Planets》2008,102(1-4):505-520
The history of associating meteor showers with asteroidal-looking objects is long, dating to before the 1983 discovery that
3200 Phaethon moves among the Geminids. Only since the more recent recognition that 2003 EH1 moves among the Quadrantids are
we certain that dormant comets are associated with meteoroid streams. Since that time, many orphan streams have found parent
bodies among the newly discovered Near Earth Objects. The seven established associations pertain mostly to showers in eccentric
or highly inclined orbits. At least 35 other objects are tentatively linked to streams in less inclined orbits that are more
difficult to distinguish from those of asteroids. There is mounting evidence that the streams originated from discrete breakup
events, rather than long episodes of gradual water vapor outgassing. If all these associations can be confirmed, they represent
a significant fraction of all dormant comets that are in near-Earth orbits, suggesting that dormant comets break at least
as frequently as the lifetime of the streams. I find that most pertain to NEOs that have not yet fully decoupled from Jupiter.
The picture that is emerging is one of rapid disintegration of comets after being captured by Jupiter, and consequently, that
objects such as 3200 Phaethon most likely originated from among the most primitive asteroids in the main belt, instead. They
too decay mostly by disintegration into comet fragments and meteoroid streams. The disintegration of dormant comets is likely
the main source of our meteor showers and the main supply of dust to the zodiacal cloud.
Editorial handling: Frans Rietmeijer. 相似文献
5.
Three bright fireballs belonging to the August θ‐Aquillid (ATA) meteor shower were photographed by the Tajikistan fireball network in 2009. Two of them are classified as the meteorite‐dropping fireballs according to the determined parameters of the atmospheric trajectories, velocities, masses, and densities. Detection of the more dense bodies among cometary meteoroids points to a heterogeneous composition of the parent comet, and supports the suggestion that some meteorites might originate in the outer solar system, in the given case from the Jupiter‐family comet reservoir. A search for the stream's parent was undertaken among the near‐Earth asteroids (NEAs); as a result, the asteroid 2004MB6 was identified as a possible progenitor of the ATA meteoroid stream. Investigation of the orbital evolution of the 2004MB6 and the fireball‐producing meteoroid TN170809A showed that both objects have similar secular variations in the orbital elements during 7 kyr. The comet‐like orbit of the 2004MB6 and its association with the ATA shower suppose a cometary origin of the asteroid. 相似文献
6.
IWAN P. WILLIAMS G. O. RYABOVA A. P. BATURIN A. M. CHERNITSOV 《Earth, Moon, and Planets》2004,95(1-4):11-18
The orbit of asteroid 2003 EH1 is very similar to the mean orbit of the Quadrantid meteoroid stream so that a close relationship
between the two is very likely. It has already been suggested that Comet C/1490 Y1 could be the parent of the Quadrantids.
If this is the case, then some relationship between the comet and the asteroid might be expected. The orbit of C/1490 Y1 is
based on a short observing arc of about 6 weeks and all the observations were with the naked eye, so that its elements are
very poorly determined. Hence, forward integration to determine whether asteroid 2003 EH1 represents the re-discovery of the
dormant nucleus of C/1490 Y1 is not feasible. Instead we choose to integrate back in time the orbit of 2003 EH1, which is
far better determined, and a family of 3500 clones, all of which are moving on an orbit that is consistent with the present
known orbit of 2003EH1. We compare the results primarily with the recorded observations of the comet rather than the orbit
of the comet derived by Hasegawa. We find that one clone is consistent with these observations. 相似文献
7.
Using a meteor orbit radar, a total of more than 2.5 million meteoroids with masses ∼10−7 kg have had orbits measured in the interval 2002-2006. From these data, a total of 45 meteoroid streams have been identified using a wavelet transform approach to isolate enhancements in radiant density in geocentric coordinates. Of the recorded streams, 12 are previously unreported or unrecognized. The survey finds >90% of all meteoroids at this size range are part of the sporadic meteoroid background. A large fraction of the radar detected streams have q<0.15 AU suggestive of a strong contribution from sungrazing comets to the meteoroid stream population currently intersecting the Earth. We find a remarkably long period of activity for the Taurid shower (almost half the year as a clearly definable radiant) and several streams notable for a high proportion of small meteoroids only, among these a strong new shower in January at the time of the Quadrantids (January Leonids). A new shower (Epsilon Perseids) has also been identified with orbital elements almost identical to Comet 96P/Machholz. 相似文献
8.
D. I. Steel 《Earth, Moon, and Planets》1995,68(1-3):13-30
Various points are discussed concerning the association of Earth-crossing asteroids (ECAs) with meteoroid streams, including the drawbacks of the techniques used in some previous work. In comparing the theoretical radiants of any ECA (or, indeed, comet) with observed meteor radiants it is necessary that the orbit used be that appropriate for epochs when the ECA has a node at 1 AU; in each precession cycle of the argument of perihelion () there will be four values rendering a node at the Earth's orbit, so that four showers are expected. Precession of the node will result in sets of showers at different times of year from different-precession cycles, whilst for some objects the orbital evolution is more convoluted. For diffuse, low-flux showers a problem is differentiating the meteors associated with any ECA from the sporadic background; a new graphical technique is introduced for illuminating whether such associations exist. A re-evaluation is required of whether ECAs should be thought of as being parent bodies of specific showers. Although this might be the case for some very large ECAs (such as (3200) Phaethon, associated with the Geminid stream), the bodies observed now being extinct or dormant cometary cores, it is suggested that in general the ECAs are better thought of as being large fragments produced in hierarchical cometary disintegrations. That is, some ECAs are just the largest meteoroids in meteoroid streams. 相似文献
9.
D. J. Asher 《Earth, Moon, and Planets》2008,102(1-4):27-33
The spatial structure of meteor streams, and the activity profiles of their corresponding meteor showers, depend firstly on
the distribution of meteoroid orbits soon after ejection from the parent comet nucleus, and secondly on the subsequent dynamical
evolution. The latter increases in importance as more time elapses. For younger structures within streams, notably the dust
trails that cause sharp meteor outbursts, it is the cometary ejection model (meteoroid production rate as a function of time
through the several months of the comet’s perihelion return, and velocity distribution of the meteoroids released) that primarily
determines the shape and width of the trail structure. This paper describes how a trail cross section can be calculated once
an ejection model has been assumed. Such calculations, if made for a range of ejection model parameters and compared with
observed parameters of storms and outbursts, can be used to constrain quantitatively the process of meteoroid ejection from
the nucleus, including the mass distribution of ejected meteoroids. 相似文献
10.
The Leonid meteor storms of 1833 and 1966 总被引：2，自引：0，他引：2
D. J. Asher 《Monthly notices of the Royal Astronomical Society》1999,307(4):919-924
The greatest Leonid meteor storms since the late eighteenth century are generally regarded as being those of 1833 and 1966. They were evidently due to dense meteoroid concentrations within the Leonid stream. At those times, the orbit of Comet 55P/Tempel–Tuttle was significantly nearer that of the Earth than at most perihelion returns, but still some tens of Earth radii away. Significantly reducing this miss distance can be critical for producing a storm. Evaluation of differential gravitational perturbations, comparing meteoroids with the comet, shows that, in 1833 and 1966 respectively, the Earth passed through meteoroid trails generated at the 1800 and 1899 returns. 相似文献
11.
Dust complexes in the Solar System are produced and maintained by different physical processes. However, one often requires equations of the same type to be studied and solved in order to mathematically describe these processes. We have analytically found earlier a shape of the complex formed when particles are ejected in a single-ejection event from a parent body orbiting a central body in a circular orbit. In the present paper, we consider a parent body moving in an arbitrary elliptical orbit and ejecting particles at the pericenter or apocenter. For illustration purposes, the theoretical results are applied to the Geminid meteoroid stream. The comparison with the results obtained by other authors shows good agreement. 相似文献
12.
Peter Jenniskens 《Icarus》2008,194(1):13-22
In an effort to identify space mission targets of interest, the association of known meteoroid streams with Near-Earth Objects (NEOs) was investigated. In addition to updating previous searches to include NEOs discovered up to January 1, 2007, a new dissimilarity criterion based on dynamical arguments was applied to evaluate the likelihood of each candidate association. The new criterion is based on the fact that the few established cases, such as 2003 EH1 and the Quadrantid stream, involve parent bodies that fragmented in the most recent nutation cycle of their secular orbital evolution. In established cases, the statistics speak strongly of an association due to the lack of NEOs in the a, e, i phase space occupied by these showers. The newly proposed associations are much more uncertain, because the odds of chance associations greatly increase as orbital inclination of the showers decreases. Forty-two plausible candidate dormant comets were identified, that deserve further scrutiny. Both comet and stream typically lack sufficient data to prove the association. Most candidate parent bodies pertain to NEOs with an aphelion distance just short of Jupiter's orbit, a perihelion distance near Earth orbit, and an eccentricity in the range 0.5-0.8. Surprisingly many have , which means that most candidate parent bodies are dormant Jupiter family comets that have not yet fully decoupled from Jupiter. Establishing these associations can provide further evidence that (mostly) dormant comets break frequently, making this the dominant mechanism for replenishing the zodiacal cloud. 相似文献
13.
P.G. Welch 《Monthly notices of the Royal Astronomical Society》2001,328(1):101-111
A new search method for locating meteoroid streams within an orbit data base and obtaining their central core orbits is introduced. The method is based on the transformation of a data base of discrete orbits into a continuous density map. Artificial data bases are used to determine if a density is statistically unlikely to occur by random chance. A search is then run to identify all density peaks within the map that correspond to the central core of a meteoroid stream. Drummond D' criterion is used as a metric within the transformation and a D' acceptability limit, D l , defines the length scale over which a discrete meteor orbit can have an influence on the density map. Examination of the search dependence on D l for both real and artificial data sets indicates an appropriate standard value. A full search is run on 5280 meteor orbits from the IAU data base, detecting 16 known major and minor meteoroid streams. New central core orbits are presented for these. No major differences from the published orbits are detected, apart from possible multi-branched structure in the southern δ Aquarids. 相似文献
14.
The Quadrantids, one of the more active of the annual meteor showers, is unusual for its strong but brief maximum within a broader background of activity. It is also notable for its recent onset, the first observation having been likely made in 1835. Until recently, no parent with a similar orbit had been observed and previous investigators concluded that the stream was quite old, with the stream's recent appearance and sharp peak attributed to a fortuitous convergence of meteoroid orbits. The discovery of the near-Earth Asteroid 2003 EH1 on an orbit very similar to that of the Quadrantids has probably unveiled the parent body of this stream [Jenniskens and Marsden, 2003. 2003 EH1 and the Quadrantids. IAU Circ. 8252]. From simulations of the orbit of this body and of meteoroids released from it at different intervals in the past, we find that both the sharp peak and recent appearance of the Quadrantids can most easily be explained by a release of meteoroids from 2003 EH1 near 1800 AD. This is supported by three lines of evidence. First, the evolution of the observed solar longitude of the Quadrantids over time is consistent with release from 2003 EH1 approximately 200 years ago. Second, numerical simulations of meteoroids released from this parent body at this time match the basic orbital characteristics of the Quadrantid stream well. Finally, these simulations also reveal that the Quadrantid core is well reproduced by a single outburst at perihelion circa 1800, whereas earlier releases result in the shower's appearance in our skies significantly prior to 1835. These results apply to the concentrated central core of the stream: the extended background was likely produced at earlier times. In fact, we find that 2003 EH1 is in a state of Kozai circulation along with a number of other comets and NEAs which may form a larger Quadrantid complex. Using the current total duration of the broader background Quadrantid activity compared to our simulations, we suggest a minimum age of ∼3500 years for the stream as a whole. This also represents the approximate lower limit for the age of the complex. We have further identified five comets as well as nine additional NEAs which may be part of the aforementioned complex, the latter all having Tisserand parameters less than three, further suggesting that the are extinct comet nuclei. 相似文献
15.
I. P. Williams 《Earth, Moon, and Planets》1996,72(1-3):321-326
The parent bodies of a number of major meteoroid streams are not in doubt and the orbits of these parents are also well determined. For these major streams individual orbits for a significant number of member meteoroids have also been determined. There is a significant spread in the determined values of the semi-major axis of individual meteoroids in a particular stream and this paper assumes that this spread is caused primarily by a variation in the ejection process and draws conclusions regarding the value of the ejection velocities from this. 相似文献
16.
I. P. Williams 《Earth, Moon, and Planets》1995,71(3):321-326
The parent bodies of a number of major meteoroid streams are not in doubt and the orbits of these parents are also well determined. For these major streams individual orbits for a significant number of member meteoroids have also been determined. There is a significant spread in the determined values of the semi-major axis of individual meteoroids in a particular stream and this paper assumes that this spread is caused primarily by a variation in the ejection process and draws conclusions regarding the value of the ejection velocities from this. 相似文献
17.
The values of the initial velocity of the meteoroids ejected from the parent bodies are small and as a result, the most of the young meteoroid streams have similar orbits to their parent bodies. Assuming that the members of the observed meteor stream evolved under the influence of gravitational perturbations mostly, Pittich [1991, Proceedings of the Conference on Dynamic of Small Bodies of the Solar System, Polish-Slovak Conference, Warsaw, October 25–28, 1988, pp. 55-61], Williams [1996, Earth, Moon, Planets
72, 321–326; 2001, Proceedings of the Meteoroids 2001 conference, Kiruna, Sweden, August 6–10, 2001, pp. 33–42] estimated the ejection velocities of the stream meteoroids. Equation relating the ejection velocity Δυ and the change Δa of the semi-major axis, Williams (2001), was applied with two slightly different variations. In the first one (M1) as Δa the difference between the mean orbit of the stream and the orbit of the parent body was substituted, in the second one (M2), as Δa the dispersion of semi-major axes around the mean orbit of the stream was used. The results obtained by these two methods are not free from discrepancies, partly explained by the particular orbital structure of the stream. Kresak [1992, Contrib. Astron. Obs. Skalnate Pleso
22, 123–130] strongly criticized the attempts to determine the initial velocities of the stream using the statistics of the meteor orbits. He argued that this is essentially impossible, because the dispersion of the initial velocities are masked by much larger measuring errors and by the accumulated effects of planetary perturbations. In our paper, we study the reliability of M1 and M2 methods. We made a numerical experiment consisting of formation of several meteor streams and their dynamical evolution over 5000 years. We ejected meteoroids particles from the comets: 1P/Halley, 2P/Encke, 55P/Tempel-Tuttle, 109P/Swift-Tuttle and from minor planets (3200) Phaethon and 2002 SY50. During the integration, the ejection velocities were estimated using both M1 and M2 methods. The results show that the velocities obtained by M1 method are unstable: too high or too low, when compared with the known ejection velocities at the time of the stream formation. On the other hand, the velocities obtained using M2 method are too small, mostly. In principle, M2 estimates the dispersion of the distribution of the ejection velocities around the mean value, not the mean value itself. Applying more accurate Equation relating Δυ and Δa we decreased the bias of the results, but not their variation observed during the evolution of the streams and the parent bodies. We have found that the variability of the estimated ejection velocities was caused mainly by the gravitational changes of the semi-major axis and eccentricity of the parent body. In brief, we have found that the reliability of the results obtained by M1 or M2 method are low, and have to be used with great care. 相似文献
18.
We examine the hypothesis about the formation of meteor streams near the Sun. Families of short-perihelion orbit comets, many of which pass just a few radii from the solar surface at perihelion and have high dust production efficiencies, are assumed to be candidates for the parent bodies of these meteor streams. Our statistical analysis of orbital and kinematic parameters for short-perihelion meteoric particles recorded at the Earth and comets from the Kreutz family and the Marsden, Kracht, and Meyer groups led us to certain conclusions regarding the proposed hypothesis. We found a correlation between the ecliptic longitude of perihelion for comet and meteor orbits and the perihelion distance. This correlation may be suggestive of either a genetic connection between the objects of these two classes or the result of an as yet unknown mechanism that equally acts on short-perihelion comet and meteor orbits. A reliable conclusion about this genetic connection can be reached for the meteors that belong to the Arietids stream and the Marsden comet group. 相似文献
19.
The Quadrantids are one of the most active annual meteor showers and have a number of unusual features. One is a sharp brief
maximum, 12–14 h in length. A second is the Quadrantids, relatively recent appearance in our skies, the first observation
having likely been made in 1835. Until recently no likely parent with a similar orbit had been observed and previous investigators
concluded that the stream was quite old, with the stream’s recent appearance and sharp peak attributed to a recent fortuitous
convergence of meteoroid orbits. The recent discovery of the near-Earth asteroid 2003 EH1 on an orbit very similar to that
of the Quadrantids has almost certainly uncovered the parent body of this stream. From the simulations of the orbit of this
body and of meteoroids released at intervals from it in the past, we find that both the sharp peak and recent appearance of
the Quadrantids can most easily be explained assuming meteoroids were ejected in substantial numbers near 1800 AD. 相似文献
20.
The ejection velocity of meteoroids from cometary nuclei deduced from observations of meteor shower outbursts 总被引：1，自引：0，他引：1
The ejection velocities of meteoroids belonging to the Leonid and Perseid meteoroid streams are deduced from the observed differences between the longitude of the ascending node of the outburst meteoroids and that of the parent comet. The difference is very sensitive to the true anomaly of the ejection point, as well as the ejection velocity, and probable values for both are discussed. 相似文献