共查询到20条相似文献,搜索用时 10 毫秒
1.
M. D. Campbell-Brown S. Close 《Monthly notices of the Royal Astronomical Society》2007,382(3):1309-1316
The Advanced Research Project Agency (ARPA) Long Range Tracking and Instrumentation Radar has recorded thousands of head echoes from small meteoroids, which include detailed trajectory information as well as ionization measurements. In total, 25 complete ionization curves have been matched using a detailed model of meteoroid ablation, though the solutions are not necessarily unique. While measurements of the spread along the trajectory of the echoes indicate that most meteors in this size range do not have large separations among fragments, the ionization curves are consistent with fragmenting bodies in the most cases. Very precise radar measurements of meteors can be a valuable source of data on the chemical and physical properties of small meteoroids. 相似文献
2.
H. McNamara J. Jones B. Kauffman R. Suggs W. Cooke S. Smith 《Earth, Moon, and Planets》2004,95(1-4):123-139
In an attempt to overcome some of the deficiencies of existing meteoroid models, NASA’s Space Environments and Effects (SEE)
Program sponsored a 3 year research effort at the University of Western Ontario. The resulting understanding of the sporadic
meteoroid environment – particularly the nature and distribution of the sporadic sources – were then incorporated into a new
Meteoroid Engineering Model (MEM) by members of the Space Environments Team at NASA’s Marshall Space Flight Center. This paper
discusses some of the revolutionary aspects of MEM which include (a) identification of the sporadic radiants with real sources
of meteoroids, such as comets, (b) a physics-based approach which yields accurate fluxes and directionality for interplanetary
spacecraft anywhere from 0.2 to 2.0 astronomical units (AU), and (c) velocity distributions obtained from theory and validated
against observation. Use of the model, which gives penetrating fluxes and average impact speeds on the surfaces of a cube-like
structure, is also described along with its current limitations and plans for future improvements. 相似文献
3.
Martin Beech 《Monthly notices of the Royal Astronomical Society》2001,326(3):937-942
Some 5 per cent of bright meteors show rapid, quasi-periodic brightness variations. It is argued that this effect, observationally known as flickering, is a manifestation of the rotational modulation of surface mass loss through ablation of a non-spherical meteoroid. We develop a set of time-dependent, single-body ablation equations that include the effect of cross-section area modulation. We present a discussion of the effects that the rotation of a non-spherical meteoroid has on the resultant meteor light curve, and we look in depth at the data related to the fireball associated with the fall of the Innisfree meteorite. We find that the parent object to the Innisfree meteorite was spinning at a rotation frequency of 2.5 Hz when it encountered the Earth's upper atmosphere. We also find that the Innisfree parent body had an initial mass of about 20 kg and that the ratio of its semiminor and semimajor axes was about 0.5. 相似文献
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We investigate the morphological variation of classical meteor light curves, under the constant velocity assumption, for a
series of idealized atmospheric density profiles. We look specifically at the t
rise
/t
fall
ratio, which compares the rise time to maximum brightness against the time to fall from maximum brightness. We demonstrate
that for a classical meteoroid undergoing rapid ablation in an isothermal atmosphere that t
rise/t
fall > 1, indicating that all such light curves are late peaked. For a classical meteoroid ablating in a region over which the
density is constant, t
rise/t
fall≡ 0, and the light curve is necessarily downward concave in the height vs. intensity diagram. If ablation occurs over a region
in which the density increases linearly with decreasing height, then t
rise/t
fall=1/(√5 – 1) ≈ 0.81, indicative of an early peaked, near symmetric light curve. 相似文献
6.
Ján Svoreň Luboš Neslušan Zuzana Kaňuchová Vladimír Porubčan 《Earth, Moon, and Planets》2004,95(1-4):69-74
A fine structure of the Perseid stream in the range of photographic magnitudes is studied using the method of indices. A new
completed 2003 version of the IAU Meteor Data Center Catalogue of 4581 photographic orbits is used. The method of indices
is used to acquire a basic data set for the Perseids. Subsequently, the method is applied on the chosen Perseids to study
their structure. Sixty four percent of chosen Perseids taken into account are attached to one of the 17 determined filaments
of orbits. The filaments are not distributed in the space accidentally, but they form a higher structure consisting of at
least four well-defined and distinguished “branches”. 相似文献
7.
We used light curve analysis to search for evidence of the dustball meteoroid model. Leonid, Taurid, Alpha Monocerotid and
sporadic meteors from November 2003 were observed and analyzed using uniform methodology. Meteors from these four sources
were examined for evidence of fragmentation by examining light curve shape and searching for light curve irregularities. Differences
in meteoroid structure should be reflected by differences in meteor light curves. The resulting meteor light curve F-parameter values showed no statistically significant differences between the meteors from the various cometary showers or
the sporadic meteors. The F-parameter values also suggest that the meteoroids from these sources do not follow a single body ablation model, which suggests
that all four sources produce meteoroids with a dustball structure. 相似文献
8.
In our work, the method that can help to predict the existence of distant objects in the Solar system is demonstrated. This
method is connected with statistical properties of a heliocentric orbital complex of meteoroids with high eccentricities.
Heliocentric meteoroid orbits with high eccentricities are escape routes for dust material from distant parental objects with
near-circular orbits to Earth-crossing orbits. Ground-based meteor observations yield trajectory information from which we
can derive their place of possible origin: comets, asteroids, and other objects (e.g. Kuiper Objects) in the Solar system
or even interstellar space. Statistical distributions of radius vectors of nodes, and other parameters of orbits of meteoroids
contain key information about position of greater bodies. We analyze meteor orbits with high eccentricities that were registered
in 1975–1976 in Kharkiv (Ukraine). The orbital data of the Kharkiv electronic catalogue are received from observations of
radiometeors with masses 10−6−10−3 g. 相似文献
9.
Martin Beech 《Monthly notices of the Royal Astronomical Society》2009,397(4):2081-2086
The shape and characteristics (beginning and end heights, and height of maximum brightness) of meteor light curves are investigated under the constraint that the surface area S that a meteoroid presents to the oncoming air flow varies as a power law in the meteoroid mass m such that S ∼ m α . We investigate the meteoroid ablation for a range of values of α, and find that the α= 1 condition allows for a fully analytic solution to the coupled differential equations of meteoroid ablation when the density profile is that of an isothermal atmosphere. The possible geometrical properties of Geminid meteoroids are discussed in terms of the α= 1 ablation model and it is shown that they are consistent with being derived from an asteroidal, rather than cometary, parent body. 相似文献
10.
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
11.
N. G. Barri 《Earth, Moon, and Planets》2008,102(1-4):395-401
This work is devoted to modeling of the transverse scattering of meteoroid fragments in the atmosphere by adopting supersonic
gas dynamics around a system of bodies. Artem’eva and Shuvalov (1996, Shock Waves, 367) and Zhdan et al. (2004, Dokl. Phys.,
315–317) found that the transverse force decreases with the increase of the distance between fragments, that is, fragments
do not separate in a transverse direction under the action of constant repulsion force. This work on the decreasing transverse
force uses the values of the transverse force coefficient by Zhdan et al. (2004, Dokl. Phys., 315–317) obtained from numerical
modeling for spheres in a supersonic flow to derive the analytical solution of the dynamic equation for a fragment. The new
model of layer-by-layer scattering of meteoroid fragments moving as a system of bodies is constructed on the basis of the
analytical solutions derived in this work and the numerical data by Zhdan et al. (2005, Dokl. Phys., 514–518). 相似文献
12.
L.A. Rogers 《Planetary and Space Science》2005,53(13):1341-1354
Conventional meteoroid theory assumes that the dominant mode of ablation (which we will refer to as thermal ablation) is by evaporation following intense heating during atmospheric flight. Light production results from excitation of ablated meteoroid atoms following collisions with atmospheric constituents. In this paper, we consider the question of whether sputtering may provide an alternative disintegration process of some importance. For meteoroids in the mass range from 10-3 to and covering a meteor velocity range from 11 to , we numerically modeled both thermal ablation and sputtering ablation during atmospheric flight. We considered three meteoroid models believed to be representative of asteroidal ( mass density), cometary () and porous cometary () meteoroid structures. Atmospheric profiles which considered the molecular compositions at different heights were use in the sputtering calculations. We find that while in many cases (particularly at low velocities and for relatively large meteoroid masses) sputtering contributes only a small amount of mass loss during atmospheric flight, in some cases sputtering is very important. For example, a porous meteoroid at will lose nearly 51% of its mass by sputtering, while a asteroidal meteoroid at will lose nearly 83% of its mass by sputtering. We argue that sputtering may explain the light production observed at very great heights in some Leonid meteors. We discuss methods to observationally test the predictions of these computations. A search for early gradual tails on meteor light curves prior to the commencement of intense thermal ablation possibly represents the most promising approach. The impact of this work will be most dramatic for very small meteoroids such as those observed with large aperture radars. The heights of ablation and decelerations observed using these systems may provide evidence for the importance of sputtering. 相似文献
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M. D. Campbell-Brown J. Jones 《Monthly notices of the Royal Astronomical Society》2006,367(2):709-716
The activity of sporadic meteors has been measured from 2002 to 2005 with the Canadian Meteor Orbit Radar. Single-station data at 29.85 MHz have been used to find the positions of the five sporadic sources visible from the Northern hemisphere, and the activity measured for each source has been corrected for observing biases. Relative fluxes and the annual variation of each source are well determined. The variations in activity are of great interest in determining the history and origin of the sporadic meteoroid population. 相似文献
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19.
The height distributions, velocity distributions and flux measurements of underdense echoes determined from meteor radar observations are significantly affected by the attenuation associated with the initial radius of meteor trains. Dual-frequency radar observations of a very large set of sporadic radar meteors at 29 and 38 MHz yield estimates of the initial train radius and its dependence on height and meteoroid speed as determined by the time-delay method. We provide empirical formulae that can be used to correct meteoroid fluxes for the effect of initial train radius at other radio frequencies. 相似文献
20.
Huan Meng 《Monthly notices of the Royal Astronomical Society》2005,359(4):1433-1436
Owing to sublimation of ice, comet nuclei eject dust particles when they are near to the sun. Those particles assume velocities and then vary their orbits to ones similar to that of the comet. The most notable difference between the orbit of the parent comet and those of the particles is their semi-major axes. This difference (Δ a ) has been widely used in modern meteor shower predictions. Observational evidence of the distribution showed that it is a function of Δ a , and the age of the dust trail. However, the relation is not well known. In this paper, a simplified relation between Δ a , the mass index ( s ) and the age of the dust trail is presented, taking the instance of a recent Leonid meteor shower. 相似文献