Meteoroid fragments dynamics: Collimation effect

There is significant evidence that some fraction of meteoric bodies is destroyed in the atmosphere. The evolution of the fragment cloud depends on a large number of factors, amound them: the meteoroid’s altitude and velocity at the moment of greakup, fragment sizes and properties of a body material. The interaction of shock waves forming in front of the fragments may lead to both an increase and decrease of the midsection area of the fragment cloud (Artem’eva & Shuvalov, 1996; Laurence et al., 2007). In this work, we consider the interaction of the fragments in a supersonic flow. The configuration properties of two spherical bodies of different radii are considered. Via numerical simulations, we calculate the pressure distribution in the flow around the two bodies for different relative positions. We construct the functions of the coefficients of transverse and drag forces from the angle between the central line of the two bodies and the flow direction for different distances between the two fragments. We find the conditions for the collimation effect, i.e., fragment involving into the wake of the leading (usually, the largest) fragment. We systematize the simulation results for drag and transverse forces and infer the basic aerodynamic properties of the meteoroid fragments.     

On the IAU 2000/2006 precession–nutation and comparison with other models and VLBI observations

In this paper, we discuss the fundamental aspects of the semi-analytical precession–nutation models that were adopted by IAU Resolutions in 2000 and 2006. We show that no significant discrepancies appear between those models (Mathews et al., J Geophys Res 107:B4, ETG 3-1–3-26, 2002, Capitaine et al., Astron Astrophys 412:567– 586, 2003) and other semi-analytical solutions or the INPOP06 numerical integration (Fienga et al., Astron Astrophys 477:315–327, 2008), especially for the quadratic terms. We also report on the most recent comparisons of the models with VLBI observations. We have employed different empirical models to fit the residuals, in attempting to characterize the nature of the observed curvature. The efficiencies of those empirical models are compared and their interpretations in terms of physical mechanisms are discussed. We show that a combination of linear and 18.6-year corrections is the most credible model for explaining the currently observed residuals, but that a longer span of observations is required before the true character of the effect can be determined. We note that the predictions from the ERA-2005 theory (Krasinsky, Celest Mech Dyn Astron 96:169–217, 2006) have diverged from recent VLBI results and suggest that the empirical nature of the ERA model is responsible.     

Error analysis regarding the calculation of nonlinear force-free field

Magnetic field extrapolation is an alternative method to study chromospheric and coronal magnetic fields. In this paper, two semi-analytical solutions of force-free fields (Low and Lou in Astrophys. J. 352:343, 1990) have been used to study the errors of nonlinear force-free (NLFF) fields based on force-free factor α. Three NLFF fields are extrapolated by approximate vertical integration (AVI) Song et al. (Astrophys. J. 649:1084, 2006), boundary integral equation (BIE) Yan and Sakurai (Sol. Phys. 195:89, 2000) and optimization (Opt.) Wiegelmann (Sol. Phys. 219:87, 2004) methods. Compared with the first semi-analytical field, it is found that the mean values of absolute relative standard deviations (RSD) of α along field lines are about 0.96–1.19, 0.63–1.07 and 0.43–0.72 for AVI, BIE and Opt. fields, respectively. While for the second semi-analytical field, they are about 0.80–1.02, 0.67–1.34 and 0.33–0.55 for AVI, BIE and Opt. fields, respectively. As for the analytical field, the calculation error of 〈|RSD|〉 is about 0.1∼0.2. It is also found that RSD does not apparently depend on the length of field line. These provide the basic estimation on the deviation of extrapolated field obtained by proposed methods from the real force-free field.     

Revisiting the radiation history of fossil meteorites from Sweden (Rebuttal to a comment by Wieler et al. On the paper by V.A. Alexeev “Radiation History of Fossil Meteorites from Sweden,” published in solar system research, 44, 311–319)

From the analysis of the data acquired for the chromite grains recovered from fossil meteorites from Sweden (Heck et al., 2004, 2008), the dependence of the exposure age of meteorites on a mass of the examined samples was obtained (Alexeev, 2010). This dependence, whatever its nature, puts into question the validity of the conclusion on a long lasting (over the course of 1–2 Myr) and substantial (by 1–2 orders of magnitude) increase in the intensity of the flux of meteorites (L-chondrites) that fell onto the Earth about 470 Myr ago. All of the fossil meteorites found in southern Sweden could be the fragments of a single meteorite that fell as a meteorite shower in the Thorsberg quarry region ∼470 Myr ago.     

73p/Schwassmann–Wachmann 3 – One Orbit after Break-Up: Search for Fragments

We report on our search campaign for the fragments of the Jupiter family cometand target of NASA's CONTOUR mission, Comet 3P/Schwassmann–Wachmann 3, one orbit revolution after the splitting of its nucleus in 1995 (Boehnhardt et al., 1995). Fragment C was found back with coma in November 1999 at 4 AU inbound and it continued to be active during the perihelion arc until at least December 2001 when we observed it last at 3.3 AU outbound. Fragment B was observed with coma between July and September 2001 when moving outbound from 2.35 to 2.75 AU. The search for other fragments including A, D (Boehnhardt et al., 1995) and E (Kodata et al., 2000a, b; Nakamura et al., 2000) in a search area of 15 × 4 arcmin starting at fragment C along direction of the extended radius vector was not successful in July and September 2001. The limiting magnitude of this search of ∼ 25 mag in R puts an upper limit on the radius of potential fragments of about 200 m (assuming albedo 0.04). The orbit deceleration parameter and the observed coma brightness of component C suggest that this object is the primary fragment that may contain a major part of the original nucleus.     

Large Meteoroid Fragmentation: Modeling the Interaction of the Chelyabinsk Meteoroid with the Atmosphere

The interaction between a large meteoroid and the atmosphere is modeled as its destruction into a cloud of fragments and vapors moving with a common shock wave. Under the action of aerodynamic forces the shape of this cloud is deformed—it is expanded in the direction transverse to the motion and compressed in the longitudinal direction. With allowance for the pressure distribution over the surface of a body varying its shape (it is assumed that the sphere is transformed into a flattened spheroid), the relation for the rate of increase in the midsection radius of a fragmented meteoroid has been obtained. This rate significantly depends on the degree of the meteoroid flattening which leads to a significantly smaller increase in the transverse size of the meteoroid along the trajectory as compared to similar models used in the literature where the influence of the body shape was not considered. The proposed model also takes into account the change in the density of the cloud of fragments due to an increase in gaps between them. An approximate analytical solution of equations of the physical theory of meteors with drag and heat transfer coefficients varying along the trajectory has been obtained for a fragmented meteoroid. The interaction of the Chelyabinsk meteoroid with the atmosphere is modeled and the solution obtained for the energy release curve is compared with the observational data.     

Explosion of a comet nucleus fragment in the earth’s atmosphere

This paper analyzes data on thermal explosions of large meteoroids in the earth’s atmosphere. The cumulative function of flux of space bodies is corrected with regard to the explosion height, which is determined, according to our approach, by maximum braking. As a result, the integral function of flux in the work [Brown, P., Spalding, R.E., ReVelle, D.O., et al., The Flux of Small Near-Earth Objects Colliding with the Earth, Nature, 2002, vol. 420, pp. 314–316] is consistent with the one we derived earlier. It is found that at least one phenomenon of those discussed in the paper by Brown et al. is a result of explosion of a comet nucleus fragment. It is shown that the Tunguska phenomenon cannot be explained within a monolithic body model.     

Stratigraphical and morphological evidence for pingo genesis in the Cerberus plains

‘Rootless’ debris cones (or pseudocraters) occur in platy, patterned ground throughout the Cerberus plains of Mars and are thought to represent the products of explosive magma-ice interaction [Lanagan et al., 2001. Geophys. Res. Lett. 28, 2365-2368; Fagents et al., 2002. In: Smellie, J.L., Chapman, M.G. (Eds.), Volcano-Ice Interaction on Earth and Mars. In: Geol. Soc. Spec. Publ., vol. 202, pp. 295-317]. Requiring lava and water interspersed, they are central to theories of multiple magmatic and aqueous flood events [Burr et al., 2002. Icarus 159, 53-73; Berman, D.C., Hartmann, W.K., 2002. Icarus 159, 1-17] and widespread sheet volcanism [Keszthelyi et al., 2000. J. Geophys. Res. 105, 15027-15049] in the region during the late Amazonian (a region reported to have been occupied by water bodies ranging from lakes to oceans [Scott et al., 1995. Map of Mars showing channels and possible paleolake basins. USGS Miscellaneous Investigations Series, Map I-2461 (1:30,000,000)]). The nature of the platy substrate is the subject of debate, with evidence given for lava [Keszthelyi et al., 2000. J. Geophys. Res. 105, 15027-15049; Plescia, J.B., 2003. Icarus 164, 79-95] and ice [Brakenridge, G.R., 1993. Lunar Planet. Sci. XXIV (Part 1), 175-176; Rice et al., 2002. Lunar Planet. Sci. XXXIII. Abstract #2026; Murray et al., 2005. Nature 434, 352-355]. The superposition relationships of cones and platy deposits in the channels of the Athabasca Valles precludes a magmatic origin, indicating later formation as permafrost mounds (or ‘pingos’), with implications for geologically recent flood volcanism, age constraints on young surfaces and recent climate change on Mars.     

An analytical model to predict the particle flux on spacecraft in the solar system

In this paper an analytical meteoroid flux model is presented which extends from 1 to 10 AU and covers a mass range from 10⁻¹⁸ to 1 g. The basic flux curve of the model by Grün et al. (1985, Icarus 62, 244–272.) is modified by an analytical multiplication factor in order to approximate the meteoroid flux as predicted by the five-populations-model from Divine (1993, J. Geophys. Res. 98(E9), 17,029–17,048.) The impact velocity distribution as a function of heliocentric distance is described by triangular and Weibull distributions. The analytical model is applied to calculate the probability that an interferometer like DARWIN or LISA may temporarily be disturbed. Also the particle flux on the Galileo, Ulysses and Cassini spacecraft is calculated and compared with measurements and predictions by other meteoroid flux models like METEM.     

Recent Experimental Results and Modelling of High-Mach-Number Jets and the Transition to Turbulence

In recent years, we have carried out experiments at the University of Rochester’s Omega laser in which supersonic, dense-plasma jets are formed by the interaction of strong shocks in a complex target assembly (Foster et al., Phys. Plasmas 9 (2002) 2251). We describe recent, significant extensions to this work, in which we consider scaling of the experiment, the transition to turbulence, and astrophysical analogues. In new work at the Omega laser, we are developing an experiment in which a jet is formed by laser ablation of a titanium foil mounted over a titanium washer with a central, cylindrical hole. Some of the resulting shocked titanium expands, cools, and accelerates through the vacuum region (the hole in the washer) and then enters a cylinder of low-density foam as a jet. We discuss the design of this new experiment and present preliminary experimental data and results of simulations using AWE hydrocodes. In each case, the high Reynolds number of the jet suggests that turbulence should develop, although this behaviour cannot be reliably modelled by present, resolution-limited simulations (because of their low-numerical Reynolds number).     

Meteoroid ablation models

The fate of entering meteoroids in atmosphere is determined by their size, velocity and substance properties. Material from ablation of small-sized meteors (roughly R≤0.01–1 cm) is mostly deposited between 120 and 80 km altitudes. Larger bodies (up to meter sizes) penetrate deeper into the atmosphere (down to 20 km altitude). Meteoroids of cometary origin typically have higher termination altitude due to substance properties and higher entry velocity. Fast meteoroids (V>30–40 km/s) may lose a part of their material at higher altitudes due to sputtering. Local flow regime realized around the falling body determines the heat transfer and mass loss processes. Classic approach to meteor interaction with atmosphere allows describing two limiting cases: – large meteoroid at relatively low altitude, where shock wave is formed (hydrodynamical models); – small meteoroid/or high altitudes – free molecule regime of interaction, which assumes no collisions between evaporated meteoroid particles. These evaporated particles form initial train, which then spreads into an ambient air due to diffusion. Ablation models should make it possible to describe physical conditions that occur around meteor body. Several self-consistent hydrodynamical models are developed, but similar models for transition and free molecule regimes are still under study. This paper reviews existing ablation models and discusses model boundaries.     

Radar Campaign to Determine the Dependence of Initial Radii of Meteor Plasma Trains on Trajectory and Orbit

Experimental and theoretical work on the transverse dimensions of meteoric plasma trains have not converged to provide generally accepted values especially uncertain is the dependence of the train radii on meteor speeds. The roles of the meteoroid structure, fragmentation and plasma processes such as ion–electron instabilities need establishing. Knowledge of the quantitative spatial distribution of plasma in meteor trains is essential for a correct interpretation of fluxes and orbital characteristics. A current project is described which employs the AMOR 26 MHz radar facility in conjunction with a frequency managed radar operating at longer wavelengths designed to measure the ionization train radii, heights, atmospheric speeds and orbits of individual meteors.     

A comparison of detection sensitivity between ALTAIR and Arecibo meteor observations: Can high power and large aperture radars detect low velocity meteor head-echoes

Meteor head-echo observations using High Power and Large Aperture (HPLA) radars have been routinely used for micrometeor studies for over a decade. The head-echo is a signal from the radar-reflective plasma region traveling with the meteoroid and its detection allows for very precise determination of instantaneous meteor altitude, velocity and deceleration. Unlike specular meteor radars (SMR), HPLA radars are diverse instruments when compared one to another. The operating frequencies range from 46 MHz to 1.29 GHz while the antenna configurations changes from 18,000 dipoles in a 300 m×300 m square array, phase arrays of dipoles to single spherical or parabolic dishes of various dimensions. Hunt et al. [Hunt, S.M., Oppenheim, M., Close, S., Brown, P.G., McKeen, F., Minardi, M., 2004. Icarus 168, 34-42] and Close et al. [Close, S., Brown, P., Campbell-Brown, M., Oppenheim, M., Colestock, P., 2007. Icarus, doi:10.1016/j.icarus.2006.09.07] recently showed, by utilizing a head-echo plasma-based model, the presence of instrumental biases in the ALTAIR VHF radar system against detecting meteors produced by very small particles (<1 μg) moving at slow (∼20 km/s) velocities due to the low head echo radar cross-section (RCS) associated with these particles. In this paper we apply the same methodology to the Arecibo 430 MHz radar and compare the results with those presented by Close et al. [Close, S., Brown, P., Campbell-Brown, M., Oppenheim, M., Colestock, P., 2007. Icarus, doi:10.1016/j.icarus.2006.09.07]. We show that, if the methodology applied by Hunt et al. [Hunt, S.M., Oppenheim, M., Close, S., Brown, P.G., McKeen, F., Minardi, M., 2004. Icarus 168, 34-42] and Close et al. [Close, S., Brown, P., Campbell-Brown, M., Oppenheim, M., Colestock, P., 2007. Icarus, doi:10.1016/j.icarus.2006.09.07] is accurate, for particles at least 1 μg or heavier, while the bias may exist for the ALTAIR measurements, it does not exist in the Arecibo data due to its greater sensitivity.     

Mass transfer in the satellite system of Neptune: implications for Triton's crater asymmetry

In this paper, we shall analyse a promising way to explain the huge crater asymmetry observed on Triton, the largest of Neptune's satellites. Triton shows, as well as many other satellites in the Solar System, a non-symmetric crater distribution on its surface. This fact is principally due to the synchronous rotation of these satellites, as shown by many theoretical works (see Shoemaker and Wolfe, Satellites of Jupiter, University of Arizona Press, Tucson, 1992, p. 277; Horedt and Neukum, Icarus 60 (1984) 710; Zahnle et al., Icarus 136 (1998) 202; Zahnle et al., Icarus 153 (2001) 111). However, on Triton the asymmetry is much more pronounced than on other satellites, and it exceeds what the models, in which the source of the craters are bodies in heliocentric orbits, can account for. For this reason, many authors (Croft et al., Icarus 99 (1992) 94; Schenk and Sobieszczyk, American Astronomical Society, DPS Meeting, Vol. 31, 1999; Zahnle et al., Icarus 153 (2001) 111) proposed that the origin for Triton's asymmetry has to be found in a swarm of bodies having planetocentric orbits, instead of heliocentric ones. Here, we analyse from a dynamical point of view the possibility that such swarm of fragments was generated by a collision between an inner satellite and a third object (a process we call ‘mass transfer’). Moreover, we discuss the possibility that the observed crater distribution on Triton comes from two populations: heliocentric bodies responsible for a few big craters, plus planetocentric bodies responsible for the big asymmetry.Finally, we discuss some implications for ground observations.     

Jet Deflection by a Quasi-Steady-State Side Wind in the Laboratory

We present experimental data on the steady state deflection of a highly supersonic jet by a side-wind in the laboratory. The use of a long interaction region enables internal shocks to fully cross the jet, leading to the development of significantly more structure in the jet than in previous work with a similar setup (Lebedev et al., 2004). The ability to control the length of the interaction region in the laboratory allows the switch between a regime representing a clumpy jet or wind and a regime similar to a slowly varying mass loss rate. The results indicate that multiple internal oblique shocks develop in the jet and the possible formation of a second working surface as the jet attempts to tunnel through the ambient medium.     

The influence of internal friction on the deformation of a damaged meteoroid

It is shown that the inclusion of the effect of internal friction on the deformation of a damaged meteoroid leads to a marked (by 10–20 km) decrease in the height of the meteoroid deceleration and, hence, the height of the energy release. The possible decrease of the role of internal friction due to “acoustic fluidization” and the penetration of impact-compressed gas through the cracks in the interior of the damaged meteoroid are discussed.     

Effects of atmospheric breakup on crater field formation

This paper investigates the physics of meteoroid breakup in the atmosphere and its implications for the observed features of strewn fields. There are several effects which cause dispersion of the meteoroid fragments: gravity, differential lift of the fragments, bow shock interaction just after breakup, centripetal separation by a rotating meteoroid, and possibly a dynamical transverse separation resulting from the crushing deceleration in the atmosphere. Of these, we show that gravity alone can produce the common pattern in which the largest crater occurs at the downrange end of the scatter ellipse. The average lift-to-drag ratio of the tumbling fragments must be less than about 10^?3, otherwise small fragments would produce small craters downrange of the main crater, and this is not generally observed. The cross-range dispersion is probably due to the combined effects of bow shock interaction, crushing deceleration, and possibly spinning of the meteoroid. A number of terrestrial strewn fields are discussed in the light of these ideas, which are formulated quantitatively for a range of meteoroid velocities, entry angles, and crushing strengths. It is found that when the crater size exceeds about 1 km, the separation between the fragments upon landing is a fraction of their own diameter, so that the crater formed by such a fragmented meteoroid is almost indistinguishable from that formed by a solid body of the same total mass and velocity.     

Energy–Momentum In The Viscous Kasner-Type Universe In Teleparallel Gravity

Using the teleparallel gravity versions of the Einstein and Landau–Lifshitz’s energy and/or momentum complexes, I obtain the energy and momentum of the universe in viscous Kasner-type cosmological models. The energy and momentum components (due to matter plus field) are found to be zero and this agree with a previous work of Rosen and Johri et al., who investigated the problem of the energy in Friedmann–Robertson–Walker (FRW) universe. The result that the total energy and momentum components of the universe in these models is zero same as Bergmann–Thomson’s energy–momentum and props the viewpoint of Tryon. Rosen found that the energy of the FRW space–time is zero, which agrees with the studies of Tryon. PACs Numbers: 04.20.-q; 04.50.+h An erratum to this article is available at .     

The orbit,atmospheric dynamics,and initial mass of the Park Forest meteorite

Abstract— The fireball accompanying the Park Forest meteorite fall (L5) was recorded by ground‐based videographers, satellite systems, infrasound, seismic, and acoustic instruments. This meteorite shower produced at least 18 kg of recovered fragments on the ground (Simon et al. 2004). By combining the satellite trajectory solution with precise ground‐based video recording from a single site, we have measured the original entry velocity for the meteoroid to be 19.5 ± 0.3 km/s. The earliest video recording of the fireball was made near the altitude of 82 km. The slope of the trajectory was 29° from the vertical, with a radiant azimuth (astronomical) of 21° and a terminal height measured by infrared satellite systems of 18 km. The meteoroid's orbit has a relatively large semi‐major axis of 2.53 ± 0.19 AU, large aphelion of 4.26 ± 0.38 AU, and low inclination. The fireball reached a peak absolute visual magnitude of ?22, with three major framentation episodes at the altitudes of 37, 29, and 22 km. Acoustic recordings of the fireball airwave suggest that fragmentation was a dominant process in production of sound and that some major fragments from the fireball remained supersonic to heights as low as ?10 km. Seismic and acoustic recordings show evidence of fragmentation at 42, 36, 29, and 17 km. Examination of implied energies/initial masses from all techniques (satellite optical, infrasound, seismic, modeling) leads us to conclude that the most probable initial mass was (11 ± 3) × 10³ kg, corresponding to an original energy of ?0.5 kt TNT (2.1 times 10¹² J) and a diameter of 1.8 m. These values correspond to an integral bolometric efficiency of 7 ± 2%. Early fragmentation ram pressures of <1 MPa and major fragmentations occurring with ram pressures of 2–5 MPa suggest that meter‐class stony near‐Earth asteroids (NEAs) have tensile strengths more than an order of magnitude lower than have been measured for ordinary chondrites. One implication of this observation is that the rotation period for small, fast‐rotating NEAs is likely to be >30 seconds.