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.     

Light Flashes Caused by Leonid Meteoroid Impacts on the Lunar Surface

In November 1999, light flashes were recorded on the Moon at the peak of the Leonid stream activity. It is likely that they were produced by the impacts of the stream particles on the lunar surface. In the present work the impacts of cometary particles are studied by solving a two-dimensional radiative-gasdynamic problem for particles of different sizes and densities; the flux of radiation of postimpact hot gas and plasma is calculated, and the luminous efficiencies are estimated, as are the sizes of the particles which could produce the observed flashes.     

Numerical simulation of the LCROSS impact experiment

This study presents the results of the numerical modeling of the Lunar Crater Observation and Sensing Satellite (LCROSS) space experiment, which is scheduled for 2009 by NASA. It is demonstrated that a spacecraft with a mass of 2 tons impacting the Moon at a velocity of 2.5 km/s creates an ejecta plume with a size of more than 100 km and a mass exceeding 100 tons. The detailed characteristics of the ejecta are given and their relation to the impactor structure is investigated.     

An estimate for the size of the area of damage on the Earth’s surface after impacts of 10–300-m asteroids

The results of calculations for the vertical fall of 10–300 m stony asteroids to the Earth are presented. Bodies with dimensions of about 50 m are shown to be most efficient from the viewpoint of destruction. At the same time, they are the most dangerous yielding the largest product of the destroyed area and probability of fall.     

Analysis of Fluorophores of Dissolved Organic Matter in the Suwannee River by Reversed-Phase Liquid Chromatography

Water Resources - Reversed-phase high performance liquid chromatography in combination with a multiwave fluorescence detector has been used to analyze the natural water of the Suwannee River for...     

Astronomical and physical aspects of the Chelyabinsk event (February 15, 2013)

Various observational data including infrasound, seismic, optical (onboard) monitoring, ground video and photo records, and evidence from witnesses of the Chelyabinsk event on February 15, 2013, have been analyzed. The extensive material gathered has provided a base for investigations of the physical properties of the object, the results of which are discussed. A bolide light curve is constructed, which shows a multiplicity of flashes. Estimations of the energy of the meteoroid explosion, which took place in the atmosphere at an altitude of about 23 km, show evidence of the formation of a high-power shock wave equivalent to 300–500 kilotons of TNT. The object diameter corresponding to this energy falls within the range 16–19 m. The trajectory of the meteor is outlined. It is preliminarily concluded that the Chelyabinsk meteorite was a representative the Apollo asteroid family.     

Numerical modeling of the formation of the Eltanin submarine impact structure

Two-and three-dimensional numerical simulations of the formation of the Eltanin submarine impact structure are described. Based on the numerical results, the impactor size can be estimated, its destruction and the subsequent motion of fragments can be described, and the initial amplitude of the tsunami wave can be determined.     

Numerical simulation of high-velocity ejecta following comet and asteroid impacts: Preliminary results

The influence of different projectile and target characteristics on the mass and velocity of high-velocity (>1 km/s) ejecta from impact craters is investigated numerically. The problem of how the computation accuracy affects the resulting ejection velocity distribution is considered.     

Evaluation of Light Flashes Caused by Impacts of Small Comets on the Surface of the Moon

Images of the dayglow of the Earth's atmosphere in the ultraviolet wavelength region obtained by the photometer of the spacecraft Dynamics Explorer revealed dark spots of the order of 50 km in diameter. These atmospheric holes were interpreted by the American physicist Frank as concentrations of water vapor formed as a result of the disintegration and vaporization of so-called small comets at high altitudes. An analysis of the same images showed that their explanation requires a frequency of comet collisions with the Earth as high as 20 events a minute! This sensational hypothesis evoked a heated scientific debate. The paper below contains an analysis of the possibility of observing Frank's hypothetical comets during their collisions with the Moon. By solving a two-dimensional radiative–gasdynamic problem, the authors demonstrate that the flashes occurring during such impacts can be observed from the Earth with ordinary telescopes.     

Determination of the height of the “meteoric explosion”

When cosmic bodies of asteroidal and cometary origin, with a size from 20 to approximately 100 m, enter dense atmospheric layers, they are destroyed with a large probability under the action of aerodynamic forces and decelerated with the transfer of their energy to the air at heights from 20–30 to several kilometers. The forming shock wave reaches the Earth’s surface and can cause considerable damage at great distances from the entry path similar to the action of a high-altitude explosion. We have performed a numerical simulation of the disruption (with allowance for evaporation of fragments) and deceleration of meteoroids having the aforesaid dimensions and entering the Earth’s atmosphere at different angles and determined the height of the equivalent explosion point generating the same shock wave as the fall of a cosmic body with the given parameters. It turns out that this height does not depend on the velocity of the body and is approximately equal to the height at which this velocity is reduced by half. The obtained results were successfully approximated by a simple analytical formula allowing one to easily determine the height of an equivalent explosion depending on the dimensions of the body, its density, and angle of entry into the atmosphere. A comparison of the obtained results with well-known approximate analytical (pancake) models is presented and an application of the obtained formula to specific events, in particular, to the fall of the Chelyabinsk meteorite on February 15, 2013, and Tunguska event of 1908, is discussed.